tag:blogger.com,1999:blog-51577858979361476562024-03-13T20:53:44.371+00:00Archaeological Geophysics with SnufflerPretty shallow earth geophysics pictures and technical discussion relating to the field of archaeology.David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.comBlogger71125tag:blogger.com,1999:blog-5157785897936147656.post-58746700386141211342022-03-29T19:42:00.001+01:002022-04-08T19:27:39.680+01:00With A Mag On Farne Street<p style="text-align: justify;">Much of my geophysics work over the past 13 years has been done, working with various groups, for a project mapping the Roman road between Hardham and Pevensey in Sussex. This encompassed Ivan Margary's "Sussex Greensand Way" (M140) and the road between Arlington and Pevensey (M142). I surmised that the two actually joined together, and set out to look for the missing piece. Starting at the Arlington end bore little fruit, so I changed to the Barcombe end, where I found the <a href="https://geophyswithsnuffler.blogspot.com/2013/02/latest-results-barcombe.html">roadside settlement</a> there, and traced the Roman road from there back to Arlington with a combination of geophysics and LiDAR. After 13 years, the entire road has now been found, with a number of corrections to Margary's original course, along with details of settlements along the road. The entire length of road has been named "Farne Street", to avoid confusion with Margary's names for individual parts of the same road. The name comes from a short section of the road near Polegate, and means 'ferny' street.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhepXEFEKC1jbYrc6dGWqN5kmZyfKroMcBeJ2kh8QbfFBImGQsN4kX6X08oPbXAYYRJljLCeDhpBauE7rHIcIeitv9_jW_zgYN5spoXPYgOSkkF-V6r5BmyeYOj3E-dQIZcmcvvwy_5XJgnaNLsc9Q18uf8uRcy9T0gnlnonD82emTcLPQXwOhX6w/s3244/overview.jpeg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1912" data-original-width="3244" height="236" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhepXEFEKC1jbYrc6dGWqN5kmZyfKroMcBeJ2kh8QbfFBImGQsN4kX6X08oPbXAYYRJljLCeDhpBauE7rHIcIeitv9_jW_zgYN5spoXPYgOSkkF-V6r5BmyeYOj3E-dQIZcmcvvwy_5XJgnaNLsc9Q18uf8uRcy9T0gnlnonD82emTcLPQXwOhX6w/w400-h236/overview.jpeg" width="400" /></a></div><p style="text-align: center;"><i>An overview of the road</i> <br /></p><p>A 65 page overview of the road has been published, entitled "With A Mag On Farne Street".<br /></p><p style="text-align: center;"><a href="https://www.archaeologyplus.co.uk/product/32773/With-a-Mag-on-Farne-Street-Version-1"><b>It can be purchased from Archaeology Plus.</b></a><br /></p><p><br /></p>David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-71110105313426217982020-09-20T14:14:00.000+01:002020-09-20T14:14:12.997+01:00Digging Up The Geophysics: Brough<p style="text-align: justify;"><a href="https://geophyswithsnuffler.blogspot.com/2018/11/latest-results-brough.html" target="_blank"> Back in 2018</a>, I was asked to do a radar survey over part of the Roman town of Petuaria. I returned in early 2019 to do a second season of geophysics, in peoples gardens surrounding the site, which unfortunately I cannot show here. I also resurveyed the possible theatre building at a higher resolution, and walking perpendicular to the first survey, which showed a number of changes to the original layout.</p><p style="text-align: justify;"><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-qp3784BUPnU/X2dJ9y3OgnI/AAAAAAAABTw/BzNOde2IYCwlfY8TKiEfRIe7LGgIabbTQCLcBGAsYHQ/s2038/brough2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="2038" data-original-width="1716" height="400" src="https://1.bp.blogspot.com/-qp3784BUPnU/X2dJ9y3OgnI/AAAAAAAABTw/BzNOde2IYCwlfY8TKiEfRIe7LGgIabbTQCLcBGAsYHQ/w336-h400/brough2.jpg" width="336" /></a></div><p></p><p style="text-align: center;"><i>Second GPR survey over the possible theatre building</i><br /></p><p>Now in 2020, part of the possible threatre has been excavated by Hull University, with a long trench across the building.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-RU-CWfMmlGo/X2dMG_r-4jI/AAAAAAAABT8/aR-JsbUQxQIDVav8TjLcdhAVi2GyP2IswCLcBGAsYHQ/s1978/trenchonly.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1978" data-original-width="1504" height="400" src="https://1.bp.blogspot.com/-RU-CWfMmlGo/X2dMG_r-4jI/AAAAAAAABT8/aR-JsbUQxQIDVav8TjLcdhAVi2GyP2IswCLcBGAsYHQ/w304-h400/trenchonly.jpg" width="304" /></a></div><div style="text-align: center;"><i>Excavation trench, and features within it</i><br /></div><p></p><p style="text-align: justify;">At the north end of the trench, the expected floor surface (G on the plan above) was found, though being gravel, it is likely that the radar was not picking up that surface, but the layer of larger stones below it. Some flat stones and tile had been inserted into the floor for use as a hearth.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-DmZtZ8LrpIw/X2dNjNNL7qI/AAAAAAAABUI/tpQtYMp_p7seM2o88rn-yiKx847alxg-QCLcBGAsYHQ/s2048/IMG_20200826_090139717_HDR.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="2048" data-original-width="1152" height="400" src="https://1.bp.blogspot.com/-DmZtZ8LrpIw/X2dNjNNL7qI/AAAAAAAABUI/tpQtYMp_p7seM2o88rn-yiKx847alxg-QCLcBGAsYHQ/w225-h400/IMG_20200826_090139717_HDR.jpg" width="225" /></a></div><div style="text-align: center;"><i>Floor layer at the north end of the trench</i><br /></div><p style="text-align: justify;">Where the stage was supposed to be (feature F on the plan above), there was a layer of rubble, which was found to be a collapsed wall, as underneath that rubble was a layer of wall plaster that had fallen flat and face down. Wall plaster had been found across the site, with multiple colours found, such as red, black, yellow, green, purple and white. It took a long time to carefully remove the wall plaster in an orderly fashion, which didn't finish until the end of the dig.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-s1-vwgd5W8Y/X2dPKaIGbhI/AAAAAAAABUU/IJB_BhO-zQE2xlr4hq8SHTe8qo_BEr3QACLcBGAsYHQ/s2048/IMG_20200826_090148039_HDR.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1152" data-original-width="2048" height="225" src="https://1.bp.blogspot.com/-s1-vwgd5W8Y/X2dPKaIGbhI/AAAAAAAABUU/IJB_BhO-zQE2xlr4hq8SHTe8qo_BEr3QACLcBGAsYHQ/w400-h225/IMG_20200826_090148039_HDR.jpg" width="400" /></a></div><div style="text-align: center;"><i>Rubble of fallen wall</i></div><div style="text-align: center;"><i> </i><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-vTkiBCvE5vs/X2dPhZWhlwI/AAAAAAAABUc/K8KOuT1-o40EWwg9NJ8wWdDBqw5WpCJegCLcBGAsYHQ/s2048/IMG_20200902_135552729.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1152" data-original-width="2048" height="225" src="https://1.bp.blogspot.com/-vTkiBCvE5vs/X2dPhZWhlwI/AAAAAAAABUc/K8KOuT1-o40EWwg9NJ8wWdDBqw5WpCJegCLcBGAsYHQ/w400-h225/IMG_20200902_135552729.jpg" width="400" /></a></div><div style="text-align: center;"><i>Layer of face down wall plaster</i></div><div style="text-align: center;"><i> </i><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-mYB3KaT4fsY/X2dQSwpt4gI/AAAAAAAABUo/Bck1WxbsRvUGb209zRkcNpUoszZv5m18QCLcBGAsYHQ/s2048/IMG_20200905_104328348.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1152" data-original-width="2048" height="225" src="https://1.bp.blogspot.com/-mYB3KaT4fsY/X2dQSwpt4gI/AAAAAAAABUo/Bck1WxbsRvUGb209zRkcNpUoszZv5m18QCLcBGAsYHQ/w400-h225/IMG_20200905_104328348.jpg" width="400" /></a></div><div style="text-align: center;"><i>A section of lifted wall plaster with paint still attached</i><br /></div><p style="text-align: justify;">Further south, things started to get a bot more murky, and controversial. The identification of the building as a theatre was in part down to the seating area, the D shape shown on the GPR results (feature D on the plan above). The feature was found as a straight, wide and thin (depth) wall. It seemed to have facing stones, and rubble core, and additional unmortared areas of flat stones arranged on both sides. It was also very thin, so would not have been any good at holding a ceiling, but would have been good for holding wooden seating. It was in the right position and right angle and right depth, for the feature seen on the GPR, but it was straight rather than curving, as was expected.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-7UrNiL6VsM4/X2dR70N7n-I/AAAAAAAABU0/Ssms_XhS_8cEVRJp2BcBT4BUZFUkwuYKQCLcBGAsYHQ/s2048/IMG_20200830_131632800.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="2048" data-original-width="1152" height="400" src="https://1.bp.blogspot.com/-7UrNiL6VsM4/X2dR70N7n-I/AAAAAAAABU0/Ssms_XhS_8cEVRJp2BcBT4BUZFUkwuYKQCLcBGAsYHQ/w225-h400/IMG_20200830_131632800.jpg" width="225" /></a></div><div style="text-align: center;"><i>'Wall' feature, part of the 'D' shaped feature?</i><br /></div><p style="text-align: justify;">That wasn't the only problem. The dating material appearing showed the building was 4th century, but the inscription showing the stage being built was robbed to make part of the military wall in the 2nd century, so the inscription could not have been referring to this building. Unfortunately, as sometimes happens when personal theories are challenged, I got rather defensive about this (sorry guys). The current prevailing interpretation is of a courtyard building, and further work is hopefully planned for next year to continue work in the same trench to hopefully resolve the matter further.<br /></p><p><br /></p><p><br /></p><p><br /></p><p><br /></p><p style="text-align: justify;"><br /></p>David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-60813779753065371892020-01-26T18:47:00.001+00:002020-01-26T18:47:57.589+00:00Snuffler Version 1.3 Released<div style="text-align: justify;">
It's been a while since the last version of Snuffler was released. At this stage, the software does most of what I need it to do for my own geophysics work, so this release, version 1.3, is mostly about requests from other people. Apart from the usual bug fixes, the new features mostly deal with hardware changes, especially relating to the RM85 and its use of the earth resistance multiplexer and the FGM650 magnetometer. It's difficult to test these things properly without having the hardware, so I have to rely on my users to help me get it right. It seems my last attempt at dealing with the multiplexer wasn't right.</div>
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Another thing reported by some of my users is that Snuffler doesn't work on Windows 10 64bit. To resolve this, I have created a 64bit build of Snuffler, if you are having trouble installing the normal 32bit version.</div>
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As usual, the lastest version can be downloaded from <a href="http://www.sussexarch.org.uk/geophys/snuffler.html">here</a>.</div>
David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-76766353777358327002019-09-15T20:52:00.000+01:002019-09-15T20:53:05.593+01:00Latest Results: Hébécrevon, France<div style="text-align: justify;">
It's not often I leave my comfort zone of doing geophysics surveys on Roman sites in the south-east of England, but my latest survey was definitely outside, being on a WWII site in France. At Hébécrevon was part of the German main line of resistance against the allied advance into France after D-Day. It was designed to slow down the advance rather than completely stop it, and in that regard was successful. The section being looked at near Hébécrevon came under attack by US forces, and is being investigated by the <a href="https://www.facebook.com/Battlefield-Archaeology-Group-128712473869603/">Battlefield Archaeology Group</a>.</div>
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The first site is a small hill overlooking a stream valley. The side of the hill had German positions among the trees, which kept the US forces at bay for a while. The field at the top of the hill was originally 3 fields, divided by hedgelines running north-south, which have now been removed. It is known that WWII positions were dug into the side of the hedgerows, to help hide them from aerial reconnaissance. Therefore, it was important to survey the field walking east-west, to highlight the ditches either side of the hedgerows into which the foxholes were dug. The northern part of the field was already under archaeological investigation, so the geophysics was limited to the southern part of the field. So what does the magnetometry show?</div>
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<a href="https://1.bp.blogspot.com/-q0J6tU_ziz4/XWmOox6hNHI/AAAAAAAABGM/nAvfm3EH-6oPrIu-duzWyzWkIk4v7rzTgCLcBGAs/s1600/fra-5nt.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1316" data-original-width="1600" height="328" src="https://1.bp.blogspot.com/-q0J6tU_ziz4/XWmOox6hNHI/AAAAAAAABGM/nAvfm3EH-6oPrIu-duzWyzWkIk4v7rzTgCLcBGAs/s400/fra-5nt.jpg" width="400" /></a></div>
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<i>Field A: +/-5nT</i></div>
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The first thing to notice is the huge number of metal dipoles across the field, due to shrapnel from bombing and the battle at the site. This makes it difficult to spot weaker features. The concentration of metal drives up the spread of readings, so if you use standard deviations to set your display bounds, you would end up around +/-10nT. You will only end up seeing the metal, and any softer features will be invisible. Conversely, if you set the display bounds too low, you would see some softer features, but you would also be swamped by thousands of tiny pieces of shrapnel, as shown below.</div>
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<a href="https://1.bp.blogspot.com/-OvJXPNyFOO8/XWmO-3ANFaI/AAAAAAAABGU/mJYL8WZDCEoDwTZ1AiPknJosp63ViaOIQCLcBGAs/s1600/fra-2nt.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1316" data-original-width="1600" height="328" src="https://1.bp.blogspot.com/-OvJXPNyFOO8/XWmO-3ANFaI/AAAAAAAABGU/mJYL8WZDCEoDwTZ1AiPknJosp63ViaOIQCLcBGAs/s400/fra-2nt.jpg" width="400" /></a></div>
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<i>Field A: +/-2nT</i></div>
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The trick is to look at images using multiple display bounds in order to get a better picture of what is going on. Take the below image for example. The display bounds are much higher, and you are left with the larger pieces of iron. This is important information, because all of the shrapnell will be small, but larger dipoles could represent pieces of iron equipment from WWII. Couple this with the position of the hedgerows, where you would expect WWII features, and you have a set of targets to excavate. A list of likely targets, A-K are shown on the image below.<br />
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<a href="https://1.bp.blogspot.com/-Bh7PKHiE0vw/XX6EOH8KW9I/AAAAAAAABHY/9uO-NPjId-QnGXPPlpXtIHkErWUEJxgUgCLcBGAsYHQ/s1600/fra-30nt.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1316" data-original-width="1600" height="328" src="https://1.bp.blogspot.com/-Bh7PKHiE0vw/XX6EOH8KW9I/AAAAAAAABHY/9uO-NPjId-QnGXPPlpXtIHkErWUEJxgUgCLcBGAsYHQ/s400/fra-30nt.jpg" width="400" /></a></div>
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<i>Field A: +/-30nT</i></div>
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Staking out the targets can provide further information. The rough<i> </i>position is found and marked, then the precise position is found by setting the range on the magnetometer higher and scanning for the highest reading. We then used a metal detector to get information about depth, size and composition of the target, to decide whether or not to dig it. Below is what we learned about each target. Many thanks to Brian for the pictures.<br />
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Feature A is the first of five features arranged in a crescent shape on an old hedgeline. It was a horizontal dipole and the metal detector suggested it was a metre deep. Excavation found the remains of an air to ground rocket fired from a typhoon, buried in the natural.<br />
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<a href="https://1.bp.blogspot.com/-S0g7muK7lbk/XX6FbAyuDbI/AAAAAAAABHk/gTMMU-7WTQMZ5Y6hOodfJqKdd5gGRCBjQCLcBGAsYHQ/s1600/featurea.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="774" data-original-width="1032" height="300" src="https://1.bp.blogspot.com/-S0g7muK7lbk/XX6FbAyuDbI/AAAAAAAABHk/gTMMU-7WTQMZ5Y6hOodfJqKdd5gGRCBjQCLcBGAsYHQ/s400/featurea.jpg" width="400" /></a></div>
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<i> Feature A</i></div>
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Feature B was a vertical dipole, with the metal detector suggesting the feature was half a metre down. Excavation revealed a foxhole dug into the hedgeline which contained American 105mm artillary shell cases and other artifacts.<br />
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<a href="https://1.bp.blogspot.com/-ZqLvBzCHsDQ/XX6GSD20n7I/AAAAAAAABHs/BlDPIYSMexEZ8R1umanG7NvSCwiihTO-wCLcBGAsYHQ/s1600/featureb.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1032" data-original-width="774" height="400" src="https://1.bp.blogspot.com/-ZqLvBzCHsDQ/XX6GSD20n7I/AAAAAAAABHs/BlDPIYSMexEZ8R1umanG7NvSCwiihTO-wCLcBGAsYHQ/s400/featureb.jpg" width="300" /></a></div>
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<i>Feature B</i></div>
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Feature C was a vertical dipole, with the metal detector suggesting it was half a metre long and a metre down. Excavation revealed the long artifact the metal detector was picking up was a case for a German M42 machine gun barrel within another foxhole.<br />
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<a href="https://1.bp.blogspot.com/-1KVh2hyTiFE/XX6HCmxH1EI/AAAAAAAABH0/ODrjnkZe25M5012zghrNN1Ms645952mNQCLcBGAsYHQ/s1600/featurec.jpeg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1031" data-original-width="581" height="400" src="https://1.bp.blogspot.com/-1KVh2hyTiFE/XX6HCmxH1EI/AAAAAAAABH0/ODrjnkZe25M5012zghrNN1Ms645952mNQCLcBGAsYHQ/s400/featurec.jpeg" width="225" /></a></div>
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<i>Feature C</i></div>
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Feature D was a vertical dipole, and the metal detector suggested the feature was sizable and half a metre down. Excavation revealed 3 gas masks and infantry equipment for a german soldier.<br />
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<a href="https://1.bp.blogspot.com/-oKfzYwrsz1w/XX6Hybr4kMI/AAAAAAAABH8/AP0nvm4C08o7fgQqBlGOP38jJnX45S9jQCLcBGAsYHQ/s1600/featured.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1032" data-original-width="774" height="400" src="https://1.bp.blogspot.com/-oKfzYwrsz1w/XX6Hybr4kMI/AAAAAAAABH8/AP0nvm4C08o7fgQqBlGOP38jJnX45S9jQCLcBGAsYHQ/s400/featured.jpg" width="300" /></a></div>
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<i>Feature D</i></div>
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Feature E was a horizontal dipole. The metal detector suggested the feature was half a metre down. Excavation found a foxhole containing more American 105mm artillary shell cases.<br />
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<a href="https://1.bp.blogspot.com/-NnDZRXaNGvg/XX6JnY4vxiI/AAAAAAAABII/D2z3IQWttR0_kZuHaKVHy__vomyLVwXZQCLcBGAsYHQ/s1600/featuree.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="774" data-original-width="1032" height="300" src="https://1.bp.blogspot.com/-NnDZRXaNGvg/XX6JnY4vxiI/AAAAAAAABII/D2z3IQWttR0_kZuHaKVHy__vomyLVwXZQCLcBGAsYHQ/s400/featuree.jpg" width="400" /></a></div>
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<i>Feature E</i></div>
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Feature F was by far the strongest feature on the magnetometry results. The metal detector suggested it was 1m down and roughly 2m square. Unfortunately, you can't win them all, as it turned out to be a section of modern metal cable.<br />
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<a href="https://1.bp.blogspot.com/-NMx27YW4IMs/XX6KKT8xQHI/AAAAAAAABIQ/jsv-Yxxfbfoa9s4hYoobEHPFpmxVVMlAgCLcBGAsYHQ/s1600/featuref.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1200" height="400" src="https://1.bp.blogspot.com/-NMx27YW4IMs/XX6KKT8xQHI/AAAAAAAABIQ/jsv-Yxxfbfoa9s4hYoobEHPFpmxVVMlAgCLcBGAsYHQ/s400/featuref.jpg" width="300" /></a></div>
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<i>Feature F</i></div>
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Feature G is a feature of two parts. There is a horizontal metal dipole on the west side of what appears to be a sizable cut. Cut features are difficult to see in these results with the amount of metal everywhere. I suggested that the cut might have been where a tank had been dug in. The metal detector suggested that the dipole was only 20cm down. At that depth, it was likely to be modern, and it did indeed turn out modern, as it was a metal pole used to hold up an electric fence. A slot was dug across the cut, but the results were inconclusive.<br />
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Feature H was a horizontal dipole in the eastern of the two hedgelines that once divided this field. The metal detector suggested it was only 20cm down, so it was decided to quickly dig it out. The metal detector turned out to be picking up something closer to the surface, and the feature generating the large dipole was actually a metre down. It was an open ammunition case lying on top of a large amount of belted ammunition.<br />
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<i>Feature H</i></div>
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Feature I initially looked like a cut feature in the middle of the field. We later found the spot was once occupied by a large tree, so is probably a silted up tree throw. We decided not to dig it.<br />
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Feature J was a horizontal metal dipole which the metal detector found to be 0.5m down and quite dispursed. It was a good target, being on the hedgeline, but it was decided that enough trenches had been opened to cover the week.<br />
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Feature K was a horizintal metal dipole which the metal detector suggested was small and 1m down. It wasn't on the hedgeline, so wasn't seen as a priority to dig.<br />
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The geophysics was a great success, identifying several features by finding their contents. Finding the ditches of the old field boundary was important to identify which features should be a priority, so walking across rather than along them was important. The combination of the magnetometer and metal detector was very useful in assessing what features should be dug and what should be ignored. It's also important on a site like this to not just accept the default display bounds for the magnetometry results, but to try different settings in order to highlight different types of feature.<br />
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Further to the west of the excavation side is a field known to have been used as part of a German road block, with tanks and machine gun positions stopping the advance of the American troops. The field was much larger than the first, and judging by the amount of metal lying about on the surface, it was going to be just as noisy as the first field.<br />
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<a href="https://1.bp.blogspot.com/-lpgYcxUGXK4/XX6TEpAq2pI/AAAAAAAABIo/AAeBQPn0dS8hwbVEz9jaCZZ04A9KTvzKgCLcBGAsYHQ/s1600/frb-2nt.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1383" height="400" src="https://1.bp.blogspot.com/-lpgYcxUGXK4/XX6TEpAq2pI/AAAAAAAABIo/AAeBQPn0dS8hwbVEz9jaCZZ04A9KTvzKgCLcBGAsYHQ/s400/frb-2nt.jpg" width="345" /></a></div>
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<i>Field B: +/-2nT</i></div>
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<i>Field B: +/-5nT</i></div>
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<a href="https://1.bp.blogspot.com/-M5BuLzFUnIE/XX6Te7n3CSI/AAAAAAAABI0/Gxj2PizrcVQAxk_MfX3-0997YwyqNHkuwCLcBGAsYHQ/s1600/frb-30nt.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1383" height="400" src="https://1.bp.blogspot.com/-M5BuLzFUnIE/XX6Te7n3CSI/AAAAAAAABI0/Gxj2PizrcVQAxk_MfX3-0997YwyqNHkuwCLcBGAsYHQ/s400/frb-30nt.jpg" width="345" /></a></div>
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<i>Field B: +/-30nT</i></div>
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Again, looking at images with different display bounds is useful, with cut features showing best at lower values and the larger chunks of metal showing best at higher values. Of particular interest is a set of features highlighted with the red arrows on the 5nT image, on which it shows best. There are two sets of broken linears here, which fit within one of the historical smaller fields that make up this now much larger field. This could be a German 'square wave' trench. As I was walking north-south, and east-west sections of trench show best, with the short connecting pieces of trench between the two lines falling between my survey lines, and are thus invisible in some cases. That's an excavation for another year.<br />
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David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-5519942981047819052018-11-22T13:52:00.000+00:002018-11-22T14:24:05.867+00:00Latest Results: Brough<div style="text-align: justify;">
Sometimes I get asked to survey a bit further afield than my home county of Sussex. I will pop over the border to Kent, Surrey or Hampshire. Recently I was asked to do a survey in Yorkshire! Despite being a very long way, it seems odd for someone from the south coast to be asked to do a geophys survey so close to Bradford, but apparently my <a href="https://geophyswithsnuffler.blogspot.com/2015/09/latest-results-chichester.html">results from Chichester</a> made me famous. I'm glad I did though, as the site is very interesting. My contribution is only a small part, as part of a larger project involving <a href="https://www.facebook.com/petuaria/">Petuaria Revisited</a>, <a href="http://elloughtonparishcouncil.eastriding.gov.uk/Default.aspx">Elloughton cum Brough PFA</a>, the <a href="http://www.romanroads.org/">Roman Roads Research Association</a>, <a href="https://www.hull.ac.uk/faculties/staff-profiles/peter-halkon.aspx">Hull University</a>, <a href="http://www.geophiz.biz/">Geophiz.biz</a> and <a href="https://www.eras.org.uk/">East Riding Archaeological Society</a>.</div>
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At the site of a Roman period ferry crossing of the River Humber, grew a town by the name of <a href="https://en.wikipedia.org/wiki/Petuaria">Petuaria</a>, progressing from a military fort to the civitas capital of the <a href="https://en.wikipedia.org/wiki/Parisi_(Yorkshire)">Parisi tribe</a>. Most of the town is now covered by the modern town of Brough, leaving just the eastern side located under a playing field. Magnetometry and earth resistance have been done at the site, but these are somewhat limited by the depth of made ground used to level the site to make the current playing field. Enter myself, with a GPR, to try to get the depth required to find the most interesting features. Despite the rain, the results were good, as the grass was short, and the geology was sandy. Some features had already been excavated back in the 1930's, before the area was scheduled, but there were many gaps in the map that needed to be filled in.</div>
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<a href="https://4.bp.blogspot.com/-WqZCSx3FMRA/W_GIwjVC98I/AAAAAAAAA-I/tLs03hPxBVICqsP7HBLSfIou3DmR7yfDACLcBGAs/s1600/brough1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1421" height="640" src="https://4.bp.blogspot.com/-WqZCSx3FMRA/W_GIwjVC98I/AAAAAAAAA-I/tLs03hPxBVICqsP7HBLSfIou3DmR7yfDACLcBGAs/s640/brough1.jpg" width="568" /></a></div>
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<i>Click for larger image</i></div>
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The eastern edge of the site is marked by a wall (pink) and associated ditch systems (purple), within which can be seen a number of building revealed by walls (light blue) and demolition rubble (dark green) aligned to a road system (light green). One building, at the western edge of the survey area is particularly large and has surviving floors (dark blue). The layout is certainly striking, but its function is not quite clear. The curving nature of part of this building possibly marks this as a theatre, which matches with a <a href="https://romaninscriptionsofbritain.org/inscriptions/707#RIB">piece of reused inscription</a> found nearby, but a forum, macellum or town house with courtyard are also possibilities.</div>
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The <a href="https://www.bbc.co.uk/news/av/uk-england-humber-46255308/scans-reveal-roman-forum-remains-in-east-yorkshire">BBC</a> have picked up the story in the local news, and I managed to make a television appearance. It would be nice to see the larger building excavated to work out its function, but that seems unlikely as the site is scheduled.David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-35841863180809999232018-07-22T19:53:00.000+01:002018-07-22T19:53:08.566+01:00Digging Up The Geophysics: 2018 Edition<div style="text-align: justify;">
Recently, I realised that there were currently five sites undergoing excavation, all in Sussex, that had targetted geophysics I had done. With my ego approaching dangerously unsafe proportions, I resolved to go on a quest, to visit all five sites in one day, and make a blog post about it. All of these sites have volunteer positions, so if you fancy a dig next year, you can join up and join in. </div>
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<u><b>Site 1: Priory Park, Chichester</b></u><br />
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After the <a href="http://geophyswithsnuffler.blogspot.com/2015/09/latest-results-chichester.html">GPR survey in 2015</a>, and a successful <a href="http://geophyswithsnuffler.blogspot.com/2017/06/digging-up-geophysics-chichester.html">first season of excavation in 2017</a>, <a href="http://www.cdas.info/">CDAS</a> returned for a second season of excavation looking at the east site of the bath house. The excavation trench was much bigger this time, and they are looking for the connection between the bath house and the Roman town house to the south. There are what seem to be robbed out walls connecting the two, which need to be confirmed on the ground. Judging by the GPS survey, the new trench covers part of last year's excavation, and the entire bath house.<br />
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<a href="https://1.bp.blogspot.com/-pyzOr_cRJpA/W0pfFOw8MeI/AAAAAAAAA4c/mO0FPtEtfU4UMw-vPMFI5srqF3W0Ef7WACLcBGAs/s1600/chichesterdig2018.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1250" data-original-width="1600" height="312" src="https://1.bp.blogspot.com/-pyzOr_cRJpA/W0pfFOw8MeI/AAAAAAAAA4c/mO0FPtEtfU4UMw-vPMFI5srqF3W0Ef7WACLcBGAs/s400/chichesterdig2018.jpg" width="400" /></a></div>
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<i>Priory Park excavations, 2017 and 2018 trenches</i></div>
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When I visited, they were only half way through the excavation, so the layout of the building wasn't completely clear yet. The picture below is of the re-cleared area from last year, showing pilae, with some floor still surviving, sticking out of the baulk. I gather from later reports that the building was not completely excavated by the end of the second week, but they had certainly made progress. Some of the pilae seemed to extend out of the south wall, which was very odd, as no additional rooms appeared on the GPR. Perhaps the building was bigger than the tiny footprint I had found.<br />
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<a href="https://4.bp.blogspot.com/-tMiFCSn2sos/W0t4-EdfdVI/AAAAAAAAA5E/QrbA9GKRoQUc9YoeOnH9zhtslrGE9OEfQCLcBGAs/s1600/IMG_20180714_110404191_HDR.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="900" data-original-width="1600" height="225" src="https://4.bp.blogspot.com/-tMiFCSn2sos/W0t4-EdfdVI/AAAAAAAAA5E/QrbA9GKRoQUc9YoeOnH9zhtslrGE9OEfQCLcBGAs/s400/IMG_20180714_110404191_HDR.jpg" width="400" /></a></div>
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<i>Priory Park bath house</i></div>
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<u><b>Site 2: Rocky Clump, Stanmer</b></u><br />
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This is a Romano-British farmstead site on the Downs north of Brighton that has been under excavation for many years by <a href="http://www.brightonarch.org.uk/">BHAS</a>. Historically, the excavation started in the clump itself, then in more recent time, moved north of the clump, and then after <a href="http://geophyswithsnuffler.blogspot.com/2012/03/latest-results-rocky-clump.html">some geophysics</a>, excavations have moved to an enclosed settlement to the south-east of the clump. The currently open trench, which is tacked onto the east edge of the last trench, covers several ditches within the settlement, in an attempt to find evidence of occupation.</div>
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<i>Rocky Clump excavations and ditches found so far</i></div>
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As you can see, a number of ditches have already been found. The feature in the corner of the inner enclosure turned out to be a solution hollow. Some of the ditches have a high flint content, seemingly placed in such a way as to suggest that their placement is deliberate. Could it be to support something above? If so, why the need for a ditch in the first place. As ever Rocky Clump excavations providing as many questions as answers.<br />
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<a href="https://4.bp.blogspot.com/-L2utsQxeD_U/W0t6uVjcU2I/AAAAAAAAA5U/QKmUA8AlNygzoZMzcN5kKArr3Q-Hc5DyQCLcBGAs/s1600/IMG_20180714_125708151.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="900" data-original-width="1600" height="225" src="https://4.bp.blogspot.com/-L2utsQxeD_U/W0t6uVjcU2I/AAAAAAAAA5U/QKmUA8AlNygzoZMzcN5kKArr3Q-Hc5DyQCLcBGAs/s400/IMG_20180714_125708151.jpg" width="400" /></a></div>
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<i> North ditch under excavation</i></div>
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<a href="https://3.bp.blogspot.com/-JG8yTXTcO9Y/W0t6liBeLRI/AAAAAAAAA5Q/NnKjDf6NaUMcpg800LvC8RJziMjal5mvQCLcBGAs/s1600/IMG_20180714_125741148.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="900" data-original-width="1600" height="225" src="https://3.bp.blogspot.com/-JG8yTXTcO9Y/W0t6liBeLRI/AAAAAAAAA5Q/NnKjDf6NaUMcpg800LvC8RJziMjal5mvQCLcBGAs/s400/IMG_20180714_125741148.jpg" width="400" /></a></div>
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<i> Flint layer on top of inner south ditch</i></div>
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I also resolved to investigate further the area between the current excavation and the clump. There are a number of large features on the earth resistance and radar where it is not quite clear whether they are archaeological or geological. I tried radar as a further complement to the earlier surveys, which managed to answer the question. The geological features are all clay-with-flints, and there is enough moisture left in the ground, despite the hot weather, to render the clay inpenetrable to radar. These are easy to spot in the results. There is a strong signal up top, then a blank area below, as the signal is attenuated by the clay. This contrasts nicely with the surrounding messiness of the chalk, which is visible to a much greater depth.<br />
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<a href="https://2.bp.blogspot.com/-ItwOw1n6Xr0/W0z4AQYiQFI/AAAAAAAAA6o/t87E8YmAnN8Pc6fb6r7Bw_8zVLvjnMURACLcBGAs/s1600/cwf.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="404" data-original-width="1600" height="100" src="https://2.bp.blogspot.com/-ItwOw1n6Xr0/W0z4AQYiQFI/AAAAAAAAA6o/t87E8YmAnN8Pc6fb6r7Bw_8zVLvjnMURACLcBGAs/s400/cwf.jpg" width="400" /></a></div>
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<i>Clay with flints in a solution hollow surrounded by chalk</i></div>
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One of the features did turn out to be much more interesting. Situated right next to Rocky Clump itself, was a circular feature. It is barely visible as an amplitude change, but is very clear as a phase change. It has a shape of a shallow, round bowl, and my best interpretation is a dew pond. There are plenty of animal bones at Rocky Clump, so it makes sense that there is a water source for the animals, if it is Roman in date.<br />
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<a href="https://2.bp.blogspot.com/-dWdVBLFWig4/W0z4bI1H9OI/AAAAAAAAA6w/M2bDJpfkE6YQUKaHteYgQp_hENnW-a-VACLcBGAs/s1600/dewpond.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="405" data-original-width="1600" height="100" src="https://2.bp.blogspot.com/-dWdVBLFWig4/W0z4bI1H9OI/AAAAAAAAA6w/M2bDJpfkE6YQUKaHteYgQp_hENnW-a-VACLcBGAs/s400/dewpond.jpg" width="400" /></a></div>
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<i>Vertical section across the centre of the possible dew pond</i></div>
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<a href="https://3.bp.blogspot.com/-80mjSkLXo8E/W0z4tocfmnI/AAAAAAAAA64/QUqdi4qE_3oNO46PSl9cllBdz4Iy4BY4ACLcBGAs/s1600/rc0718ue-9_0ns.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="818" data-original-width="1600" height="203" src="https://3.bp.blogspot.com/-80mjSkLXo8E/W0z4tocfmnI/AAAAAAAAA64/QUqdi4qE_3oNO46PSl9cllBdz4Iy4BY4ACLcBGAs/s400/rc0718ue-9_0ns.jpg" width="400" /></a></div>
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<i>Possible dew pond, top left</i></div>
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<u><b>Site 3: Plumpton Roman Villa</b></u></div>
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Ok, for this site, I only set out the grids and processed the data. The survey itself was done by someone else. That still counts, right? The site has been under excavation by the <a href="https://www.sussexarchaeology.org/">Sussex School of Archaeology</a> for a few years now, starting at the east end of the villa building and working west. The western end, which is now under excavation, seems to be interpreted as a bath house. Below is the current excavation trench, overlayed on earth resistance of the site. Some of the southerly walls do not show up well on the geophys, as there is a higher content of chalk there compared to the use of flint in the north. I have not recorded the more substantial western end in the plan below, as that is still to be fully revealed by excavation.<br />
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<a href="https://2.bp.blogspot.com/-xXdt3yZZoLA/W0uOhlNPB_I/AAAAAAAAA5k/HxXf5lYa1IAuh3JBIOo82bTfcJW59Y-HwCLcBGAs/s1600/plumptondig2018.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1250" data-original-width="1600" height="312" src="https://2.bp.blogspot.com/-xXdt3yZZoLA/W0uOhlNPB_I/AAAAAAAAA5k/HxXf5lYa1IAuh3JBIOo82bTfcJW59Y-HwCLcBGAs/s400/plumptondig2018.jpg" width="400" /></a></div>
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<i>Plumpton excavation trench and exposed walls, 2018</i></div>
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<a href="https://3.bp.blogspot.com/-uniX0OYJhP0/W0uPjAOqcxI/AAAAAAAAA5w/zKbICwP6hUcgdGEfB71fODRy4fnyMuBtQCLcBGAs/s1600/IMG_20180714_133832482.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="900" data-original-width="1600" height="225" src="https://3.bp.blogspot.com/-uniX0OYJhP0/W0uPjAOqcxI/AAAAAAAAA5w/zKbICwP6hUcgdGEfB71fODRy4fnyMuBtQCLcBGAs/s400/IMG_20180714_133832482.jpg" width="400" /></a></div>
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<i> View from the south, looking as the chalk wall foundations</i></div>
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<a href="https://4.bp.blogspot.com/-OYfVJRrFFRU/W0uPywMKrbI/AAAAAAAAA50/vCdwuMNthnw-62bBeIvALiS-kkebI-eZQCLcBGAs/s1600/IMG_20180714_140259949.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="900" data-original-width="1600" height="225" src="https://4.bp.blogspot.com/-OYfVJRrFFRU/W0uPywMKrbI/AAAAAAAAA50/vCdwuMNthnw-62bBeIvALiS-kkebI-eZQCLcBGAs/s400/IMG_20180714_140259949.jpg" width="400" /></a></div>
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<i>More substantial foundations on the north side</i></div>
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<u><b>Site 4: Barcombe Roman roadside settlement</b></u><br />
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I started surveying this massive site <a href="http://geophyswithsnuffler.blogspot.com/2013/02/latest-results-barcombe.html">back in 2011</a>, and it is currently under excavation by the <a href="http://culverproject.co.uk/">Culver Archaeological Project</a>. This year, they moved to the centre of the defended settlement, in the hopes of finding the footprints of buildings. What postholes they have found so far don't quite resolve themselves into buildings yet. Instead, there seems to be a lot of kiln features, though whether these are industrial features, or something domestic, like corn drying, is not quite clear yet. You can see the current excavation area highlighted in the images below. If we change the display bounds to a higher value, it makes it easier to see which features are more likely to be industrial in nature. The black demolition layer visible in other trenches is also present here, so it must have been quite an event. What's left of the road surface is very close to the surface, so no surprise it is being plouged away. The trench is a rather large 20m x 45m, so they certainly have a large area to investigate. They will be back here next year.<br />
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<i>Magnetometry, 3nT display boundary </i></div>
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<a href="https://4.bp.blogspot.com/-kYiL9xa_tnY/W1TMqz0WFnI/AAAAAAAAA7s/rDCGm_fWBPMTZ006tTjKj5p1Rkz0B8iGwCLcBGAs/s1600/ClipboardView20.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1600" height="320" src="https://4.bp.blogspot.com/-kYiL9xa_tnY/W1TMqz0WFnI/AAAAAAAAA7s/rDCGm_fWBPMTZ006tTjKj5p1Rkz0B8iGwCLcBGAs/s320/ClipboardView20.png" width="320" /></a></div>
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<i>Magnetometry, 20nT display boundary</i></div>
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<a href="https://4.bp.blogspot.com/-X2f-YW_YIJ0/W0zykstfOhI/AAAAAAAAA6E/c3Z9v1G-df0nChqxUKhJhcOviheFgrR4ACLcBGAs/s1600/IMG_20180707_150355500.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="900" data-original-width="1600" height="225" src="https://4.bp.blogspot.com/-X2f-YW_YIJ0/W0zykstfOhI/AAAAAAAAA6E/c3Z9v1G-df0nChqxUKhJhcOviheFgrR4ACLcBGAs/s400/IMG_20180707_150355500.jpg" width="400" /></a></div>
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<i>One of the kilns. Site supervisor for scale</i></div>
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<u><b>Site 5: Jevington Church</b></u><br />
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Jevington are extending their churchyard, and I was asked by <a href="http://www.eastbournearchaeology.org.uk/">ENHAS</a> to survey the area ahead of an investigation. The magnetometer was pretty useless in such a small fenced field, but the GPR came up with some results, despite problems with the encoder wheel, thankfully now fixed. At the northern end of the field seemed to be an old track, leading to the church, surrounded by some solid features. I originally thought these might be grave furniture, but one of them, under excavation, turned out to be the rather boring concrete footing for an old fence post. The track itself was composed of gravel. Further to the south, the tenuously identified plague pit turned out to be a scatter of neolithic struck flint, which was much more interesting than a fence post.</div>
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<a href="https://2.bp.blogspot.com/-GYVcJwdk5DY/W1SbltT4ZuI/AAAAAAAAA7Q/w0TePSW7JVsWRKQKmu-t43rowlssGNMigCLcBGAs/s1600/jevtrenches.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1064" height="400" src="https://2.bp.blogspot.com/-GYVcJwdk5DY/W1SbltT4ZuI/AAAAAAAAA7Q/w0TePSW7JVsWRKQKmu-t43rowlssGNMigCLcBGAs/s400/jevtrenches.jpg" width="265" /></a></div>
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<i> Some of the features found at Jevington and the trenches opened to investigate them</i></div>
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<a href="https://3.bp.blogspot.com/-B8fTWrRBYDU/W0z0CcH0lOI/AAAAAAAAA6Q/Svc87Yl4gMMIlhL9CmPJlSIVe4aqlZ8UQCLcBGAs/s1600/IMG_20180714_151759904.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="900" height="400" src="https://3.bp.blogspot.com/-B8fTWrRBYDU/W0z0CcH0lOI/AAAAAAAAA6Q/Svc87Yl4gMMIlhL9CmPJlSIVe4aqlZ8UQCLcBGAs/s400/IMG_20180714_151759904.jpg" width="225" /></a></div>
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<i>Concrete post footing</i></div>
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<a href="https://1.bp.blogspot.com/-M84u3J5rOU8/W1TKcgiSpaI/AAAAAAAAA7g/7syXBo2bFiMxb_wNM6XbekJRui7kgVNAACLcBGAs/s1600/flintscatter.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1072" data-original-width="1600" height="267" src="https://1.bp.blogspot.com/-M84u3J5rOU8/W1TKcgiSpaI/AAAAAAAAA7g/7syXBo2bFiMxb_wNM6XbekJRui7kgVNAACLcBGAs/s400/flintscatter.jpg" width="400" /></a></div>
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<i>Neolithic flint scatter. Photo courtesy of Martin Jeffery</i></div>
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<br />David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-78640321502660880012017-08-14T21:19:00.000+01:002017-08-14T21:19:12.487+01:00Latest Results: Bodiam<div style="text-align: justify;">
I was recently asked by the owners of Quarry Farm, Bodiam, to look at the Roman roadside settlement on their land, which is right up my (Roman) street. They were kind enough to put me up in their <a href="http://www.original-huts.co.uk/">fantastic glamping site</a>, with views across the settlement to the castle :</div>
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<a href="https://3.bp.blogspot.com/-IIh-FQ_itio/WYgG8AW7P_I/AAAAAAAAAzk/3A1DU6W4mR4u_r7FylERBOPrGnuVwRHfACLcBGAs/s1600/IMG_20170401_130537226_HDR.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="900" height="640" src="https://3.bp.blogspot.com/-IIh-FQ_itio/WYgG8AW7P_I/AAAAAAAAAzk/3A1DU6W4mR4u_r7FylERBOPrGnuVwRHfACLcBGAs/s640/IMG_20170401_130537226_HDR.jpg" width="360" /></a></div>
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<i>View to the castle from the glamping hut</i></div>
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The site was excavated back in the 1960's, when the Battle and District Historical Society dug up a Roman building with Classis Britannica stamped tiles associated with it. The Roman road broadly follows the modern road across the floodplain, and the presence of the CL:BR stamped tiles in the floodplain has led to the interpretation of the site as a port. Further to the south, as the land rises out of the floodplain, some iron slag has been found, suggesting an iron working site.</div>
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Lidar shows up an interesting feature in the floodplain, an embanked paleochannel that cuts much further south than the current course of the river. It has been suggested that the river was redirected further north in medieval times to help fill the moat. Also look at the two fields just south of the floodplain, and notice that the field on the left is significantly higher than the field on the right.</div>
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<a href="https://4.bp.blogspot.com/-w7c6jSMEC3w/WYgKyxu6IOI/AAAAAAAAAzw/Imin753L_L8LaE3oJdwWj88pSNUl9HjBwCLcBGAs/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1396" height="400" src="https://4.bp.blogspot.com/-w7c6jSMEC3w/WYgKyxu6IOI/AAAAAAAAAzw/Imin753L_L8LaE3oJdwWj88pSNUl9HjBwCLcBGAs/s400/fig1.jpg" width="348" /></a></div>
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<i>lidar of the site, click for larger image</i></div>
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So what about the geophysics? Starting with magnetometry, the reason for the height difference between the two fields is obvious, as there is a medium sized iron working site, whose slag heap has raised the level of that field compared to the one next door. You can also see a slag metalled track leading from the Roman road (to the east) to the iron working site. The floodplain is not so easy to interpret. There is a lot of metal junk, geological features, and material from the railway and modern road. It's difficult to say with certainty from the magnetometry that anything in there is Roman, despite the amount of Roman material found in excavation.</div>
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<a href="https://4.bp.blogspot.com/-WBwk9ECSEsE/WYgL25VYFvI/AAAAAAAAAz8/JLT1kGQF8PYM7doxjTVAwFfL4mH6rV5uQCLcBGAs/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1385" height="400" src="https://4.bp.blogspot.com/-WBwk9ECSEsE/WYgL25VYFvI/AAAAAAAAAz8/JLT1kGQF8PYM7doxjTVAwFfL4mH6rV5uQCLcBGAs/s400/fig3.jpg" width="345" /></a></div>
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<i>Magnetometry, click for larger image</i></div>
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It's down to the radar to help sort the mess out. The orange lines mark out the areas surveyed with GPR. The black rectangle is the Battle and District Historical Society excavation area, in which was found the building they excavated. That building doesn't show up on the radar, which is not surprising, as the excavations were described as waterlogged, and GPR doesn't do well with wet alluvium. There is what looks like new building just next to it though, closer to the road. Most interesting though is an oval bowl shaped feature surround on three sides by hard standing. My gut says this is an upstream port, but the paleochannel seems to go through it rather than by the side of it, so I'm not sure what to make of it.</div>
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<a href="https://3.bp.blogspot.com/-y5UZSls6UfE/WYgOyWI5AfI/AAAAAAAAA0I/_LXjJEwdVkY3jIbcUvKSgBDE2xwyKEGiQCLcBGAs/s1600/fig13.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1248" height="400" src="https://3.bp.blogspot.com/-y5UZSls6UfE/WYgOyWI5AfI/AAAAAAAAA0I/_LXjJEwdVkY3jIbcUvKSgBDE2xwyKEGiQCLcBGAs/s400/fig13.jpg" width="311" /></a></div>
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<i>Interpretation of floodplain GPR, click for larger image</i></div>
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Back at the iron-working site, the radar showed the extent of the slag heap as an amplitude change on the enveloped data, and also showed the location of three bloomeries as circular phase change features on the unenveloped data.</div>
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<a href="https://3.bp.blogspot.com/-teFza3ZU_Og/WZID1qPuCvI/AAAAAAAAA00/I64M2_ehktQro5NKHIy_6i8IJtPf9JKxgCLcBGAs/s1600/fig14.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1600" data-original-width="1248" height="400" src="https://3.bp.blogspot.com/-teFza3ZU_Og/WZID1qPuCvI/AAAAAAAAA00/I64M2_ehktQro5NKHIy_6i8IJtPf9JKxgCLcBGAs/s400/fig14.jpg" width="311" /></a></div>
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<i>Interpretation of iron working GPR, click for larger image</i></div>
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So there's a lot going on, but not quite as large a settlement as expected. If you want to know more, you can read the full report <a href="https://www.scribd.com/document/356299146/Snuffler-1706">here</a>.David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-92026245631271269212017-06-16T21:14:00.000+01:002017-06-16T21:14:11.249+01:00Digging Up The Geophysics: Chichester<div style="text-align: justify;">
A couple of years ago, <a href="http://geophyswithsnuffler.blogspot.co.uk/2015/09/latest-results-chichester.html">I did some radar surveys in Priory Park, Chichester</a>. After a small test pit dug by <a href="http://www.cdas.info/">CDAS</a> last year, there was <a href="http://www.chichester.gov.uk/article/28209/Remarkable-discovery-as-Roman-houses-are-identified-under-city-centre-park">an official press release by Chichester District Council</a>, which then led to <a href="https://www.theguardian.com/uk-news/2017/jan/26/foundations-of-three-roman-houses-found-under-chichester-park">an</a> <a href="https://uk.news.yahoo.com/archaeologists-find-remains-of-three-roman-houses-right-under-city-centre-park-155425679.html">awful</a> <a href="http://www.belfasttelegraph.co.uk/news/uk/remains-of-nearcomplete-roman-buildings-found-under-chichester-park-35399269.html">lot</a> <a href="http://www.portsmouth.co.uk/our-region/west-sussex/remains-of-roman-buildings-found-under-chichester-car-park-1-7790895">of</a> <a href="http://www.bbc.co.uk/news/uk-england-sussex-38746952">press</a> <a href="http://www.archaeology.org/news/5228-170126-england-roman-chichester">coverage</a> (some of them actually managed to spell my name right), and me appearing on South Today briefly. Then this year, there was a bigger excavation run by the council and CDAS that produced <a href="http://www.bbc.co.uk/news/uk-england-sussex-40103605">even</a> <a href="https://www.theguardian.com/uk-news/2017/may/31/luxury-bath-house-from-roman-chichester-unearthed-by-archaeologists">more</a> <a href="https://www.chichester.news/news/community/soaked-history-priory-park-dig-reveals-chichesters-roman-elite-enjoyed-private-bath-house/">press</a> <a href="http://www.archaeology.org/news/5593-170531-roman-chichester-bath">coverage</a>. Here are a few more details about it all than you may not have heard about in the press.</div>
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<a href="https://1.bp.blogspot.com/-CBrbeWAcE3c/WUQ2JrriMUI/AAAAAAAAAvo/eKVC31G7BzInKWZiAhf19YT8bOEC4fLNgCLcBGAs/s1600/priorypark2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="300" src="https://1.bp.blogspot.com/-CBrbeWAcE3c/WUQ2JrriMUI/AAAAAAAAAvo/eKVC31G7BzInKWZiAhf19YT8bOEC4fLNgCLcBGAs/s400/priorypark2.jpg" width="400" /></a></div>
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<i>Click for larger image</i></div>
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If you look at the above image, the test pit from last year is on the western end of the building marked 'B', targetting the surviving floors, while the larger trench from this year targets the smaller building marked 'C'.</div>
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<a href="https://4.bp.blogspot.com/-yYvSBum_6_A/WUQ319AofkI/AAAAAAAAAvs/HI08cAPcvMQbQvge31MGjTQAXDfauBsOQCLcBGAs/s1600/pptrench.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="724" data-original-width="1600" height="180" src="https://4.bp.blogspot.com/-yYvSBum_6_A/WUQ319AofkI/AAAAAAAAAvs/HI08cAPcvMQbQvge31MGjTQAXDfauBsOQCLcBGAs/s400/pptrench.jpg" width="400" /></a></div>
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<i>Click for larger image</i></div>
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What is left of the floor fills most of the test pit in the above image, unfortunately with no surviving mosaics. There are walls to the west and north, with a cut representing a robber trench for another wall to the east, over which can be seen part of the remaining floor in the next room<br />
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<a href="https://2.bp.blogspot.com/-tbndpeI_F3k/WUQ5iyPlTZI/AAAAAAAAAvw/ZnUFdR1sGFIopG2MQ2x0XTGaCWiNa9VkwCLcBGAs/s1600/DSC_0114a.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="940" data-original-width="1600" height="235" src="https://2.bp.blogspot.com/-tbndpeI_F3k/WUQ5iyPlTZI/AAAAAAAAAvw/ZnUFdR1sGFIopG2MQ2x0XTGaCWiNa9VkwCLcBGAs/s400/DSC_0114a.jpg" width="400" /></a></div>
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<i>Click for larger image</i></div>
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The above image shows the southern end of the larger trench from this year, looking west. The funny shape of the end of the wall visible in the radar is also visible in plan. The stacks of tile are pilae forming part of a hypocaust heating system, over which would have been an opus floor, part of which is visible sticking out of the baulk at the bottom of the image. That floor, and the pilae, don't appear on the radar data though, so clay products don't seem to have a difference in contrast to the local soil. The building is most likely a small bath house, which despite being built next to the building to the north, is actually attached to the building to the south. This distance is so that if the building goes up in flames because of the under floor heating, the rest of the building is not threatened. Dating seems to suggest a date for the building in the last Roman period.</div>
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Congratulations to Chichester on a fantastic dig, and watch this space for more results if they dig more next year.</div>
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<br />David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com2tag:blogger.com,1999:blog-5157785897936147656.post-74367691930644246602017-04-06T21:06:00.000+01:002017-04-06T21:06:31.916+01:00NSGG Conference 2016It's been a few months since the <a href="http://www.nsgg.org.uk/meetings/2016/NSGG2016-Abstracts.pdf">NSGG conference in December 2016</a>, so it's about time I did my usual post about my favourite bits.<br />
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Erica Utsi, whose name is on my GPR and is <a href="https://www.elsevier.com/books/ground-penetrating-radar/utsi/978-0-08-102216-0">shortly to publish a book</a> recently became a TV star after appearing on a program about William Shakespeare's grave, and given we were a specialist audience rather than the TV viewing public, we got a slightly more in depth explanation of what it was all about, which was that Shakespeare's head may have been nicked due to a fashion for collecting the skulls of famous people.</div>
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Adam Booth treated us to some technology not often linked to the sort of geophysics we do, portable x-ray fluorescence, which can be used to identify the elements present in a sample, without having to a lab. His test site was the site of a WWII plane crash. Parts of the plane were visible on magnetometry, so what did the new tech turn up to go with that? In a transect across the site, a spike in copper and zinc from the remains of the plane leaching into the surrounding soil was visible. I've seen a similar talk where the technology was used in industrial sites, where it was suggested that it was useful for identifying prehistoric metal working, which may have been little more than a campfire affair. Always nice to see new tech explained.</div>
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My favourite subject, Roman roads, got a mention by Joep Orbons, who had thrown quite a few geophysics techniques (EM, Mag, ER, ERT and GPR) at a section of Roman road in Belgium. The sort of results he got were very familiar to me, with differences in preservation and different soil conditions giving different results of quite a small area, with some techniques (GPR, ER) performing better than others. Sometimes even massive features like this can be hard to find. Not content with one talk on Roman roads, that last talk was immediately followed by Michal Pisz taking about the Roman fort of Tibiscum in Romania with the Roman roads and surrounding vicus being surveyed and excavated.</div>
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Already mentioned in this blog, Chris Lockyear has been producing some amazing results on the Roman town of Verulanium here in the UK, with multiple buildings, roads and an aqueduct visible in surveys carried out using ER, Mag and GPR. The preservation is fantastic, and I really hope they find a lot more like it. If you haven't seen it already, <a href="https://hertsgeosurvey.wordpress.com/2016/08/30/a-picture-is-worth-a-1000-words/">check out their blog</a>. Talking of big, pretty surveys, Tomasz Herbich spoke after Chris and has been researching ancient towns in Egypt, with predictably decent results from magnetometry due to the use of fired brick.</div>
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H Webber suggested a new avenue of research for archaeologists, using the vast geophysical surveys, such as EM, carried out for the benefit of farmers in modern day precision agriculture. Phosphates present in occupation material may highlight areas of occupation that the archaeological community were not previously aware of. Of course, the farmers would have to be approached in order to get this data, and someone in the audience pointed out that if all of this was explained to the farmers, some of them might deep plough the sites away in order to bring the free fertiliser to the surface.</div>
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Petra Schneidhofer gave us a talk about the state of geophysics in Norway and Denmark. Apparently, igneous geologies make our usual favourite, magnetometry, rather pointless, so GPR is commonly used instead. despite that, the natural variation over an area in GPR is quite extreme, and it can be quite difficult to pick out features. Thanks goodness for the boring sedimentary geologies in my part of the world.</div>
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David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-33131005242585324042017-04-06T20:06:00.001+01:002017-04-06T22:35:32.185+01:00All the little geophysical surveys<div style="text-align: justify;">
It's that time of year when the weather is getting a bit warmer and it is time for me to wander once more into the green fields of England, with a machine that goes beep, to find the lost wossnames of times past. It isn't just my own Roman period projects that I work on though, I also do work for various local societies, as many don't have their own geophysics equipment. Here's a selection of projects that I've been involved with recently.</div>
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<b>The Pepperpot, Brighton</b><br />
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At the end of Tower Road, Brighton, there is a tower (no surprise there) which apparently used to house pumping equipment for a well that supplied the Attree Villa and estate. There was apparently a water tank and an underground tunnel under what is now the road, and <a href="http://www.brightonarch.org.uk/">Brighton and Hove Archaeological Society</a> along with the <a href="https://www.facebook.com/Friends-of-the-Pepperpot-327975608727/">Friends of the Pepperpot</a> asked me to take a look with my radar. There were signs of rubble in the area where the water tank would have been, and very vague signs of the tunnel, but the results weren't all that clear. You can <a href="https://www.scribd.com/document/344178095/Snuffler-1703">see the full report here</a>.</div>
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<i>The interpretation of the GPR survey over an old map of the area around the Pepperpot</i></div>
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<b>Butts Brow Neolithic Enclosure, Eastbourne</b><br />
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Though mostly filled with a combination of car park and a clump of trees, there is a second neolithic enclosure above Willingdon, Eastbourne (the first being the more well known Combe Hill causewayed enclosure). After a season of excavation targetting the surviving sections of bank and ditch by the <a href="http://www.eastbournearchaeology.org.uk/">Eastbourne Natural History and Archaeology Society</a>, I was asked to see if I could find them some internal features to dig up. It's rather difficult to see cuts in chalk with radar, especially with modern tracks and bands of natural flint around, but the ditch was slightly visible as a negative feature cutting through the flint layers. It's the dark band in the image below. The contrast between the ditch and surrounding chalk was very slight though, so smaller internal features were not visible. You can <a href="https://www.scribd.com/document/344179689/Snuffler-1704">see the full report here</a> and you can <a href="https://www.youtube.com/watch?v=ntMondpTWus">see a video of the results here</a>. Details of a dig this summer will be published <a href="http://www.eastbournemuseums.co.uk/">here</a> at some point.</div>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://2.bp.blogspot.com/-iqBEr8g8ffU/WOVF12m8RVI/AAAAAAAAAt8/ux6M7-ZHNL0gobBpojyUxzCZA3vLsfeRACLcB/s1600/buttsbrow17-28.1ns.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="https://2.bp.blogspot.com/-iqBEr8g8ffU/WOVF12m8RVI/AAAAAAAAAt8/ux6M7-ZHNL0gobBpojyUxzCZA3vLsfeRACLcB/s640/buttsbrow17-28.1ns.png" width="484" /></a></div>
<div style="text-align: center;">
<i>The neolithic ditch cutting through a band of natural flint</i></div>
<br />
<b>Southborough Post Mill</b><br />
<br />
<div style="text-align: justify;">
Just over the border into Kent this time, the Southborough and <a href="https://www.facebook.com/Shaas.online/">High Brooms Amateur Archaeological Society</a> asked me to look at a platform in the woods of Southborough Common, the site of a post mill. Geophysics surveys in woodlands are never easy, and while the woods had been cleared, some trees remained. Both earth resistance and magnetometry were used, the results of which are in the <a href="http://geophyswithsnuffler.blogspot.co.uk/2013/01/version-11-of-snuffler-released.html">channel merge</a> image below. The magnetometry didn't show much apart from a big chunk of metal and some surrounding (no longer visible) fencing, the earth resistance showed a high resistance area on the east side of the platform, which may have been the site of the mill. You can <a href="https://www.scribd.com/document/344289055/Snuffler-1702">see the full report here</a>.</div>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-J-5cWvMSt2I/WOaQBVaav6I/AAAAAAAAAuM/PVuFF6mdUh848_tAwM8PzGNavENF9jB8wCLcB/s1600/tunmerge.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="https://1.bp.blogspot.com/-J-5cWvMSt2I/WOaQBVaav6I/AAAAAAAAAuM/PVuFF6mdUh848_tAwM8PzGNavENF9jB8wCLcB/s400/tunmerge.png" width="400" /></a></div>
<div style="text-align: center;">
<i>Earth resistance in green and magnetometry in red.</i></div>
<br />
<br />
<br />
<br />David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-8515177229740005172016-12-29T12:02:00.001+00:002016-12-29T12:02:13.294+00:00Equipment Test: Earth Resistance<div align="center" lang="zxx" style="margin-bottom: 0cm;">
<span style="font-size: large;"><b>Earth
Resistance Meters – A Review</b></span></div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm;">
<b>Introduction</b></div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
The twin-probe earth
resistance meter, being relatively cheap, is often the first piece of
geophysics equipment purchased by local archaeological societies.
While it may not be the first port of call if you have access to a
magnetometer or GPR, there are many situations where it is superior.
I've found that earth resistance is the most reliable method for
finding Roman roads. Recently, I've had access to multiple pieces of
equipment, so I have decided to do a review.</div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
The first of the three
machines is the Geoscan RM15. Now replaced by the RM85, which
unfortunately I don't have access to, the only major differences that
I'm aware of is the inclusion of the multiplexer within the box
rather than as an add-on, GPS logging and output via USB instead of
the old serial port. If there are further changes that would change
this review, I apologise to Geoscan now.</div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
The second machine is the TR
Systems meter, which was aimed at local societies and proved very
popular before production ceased. Though it is not available any
more, its use is so widespread that I include it here for comparison
purposes, as many will be familiar with it.</div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
The third machine is the
Frobisher TAR-3, a relative newcomer, and like the TR Systems meter,
affordable by local societies on a budget.</div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br />
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm;">
<div lang="zxx" style="margin-bottom: 0cm;">
<b>User Interface</b></div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm;">
The best way to introduce
this section is with images of the interfaces of each machine.</div>
</div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm;">
<div style="text-align: center;">
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://3.bp.blogspot.com/-Oh-LM5ULMBk/WGT5oimXnDI/AAAAAAAAAr8/cDKBPTz2tJsdWg736C55INILLCcHFtd-gCLcB/s1600/RM15iface.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="225" src="https://3.bp.blogspot.com/-Oh-LM5ULMBk/WGT5oimXnDI/AAAAAAAAAr8/cDKBPTz2tJsdWg736C55INILLCcHFtd-gCLcB/s400/RM15iface.jpg" width="400" /> </a></div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div align="center" lang="zxx" style="margin-bottom: 0cm;">
<i>Geoscan
RM15 Interface</i></div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-yxrrnTkfJok/WGT5jmxBN5I/AAAAAAAAAr4/Dm4Xtca_1qUkkYXUKvVFSN8e65U3VoVzgCLcB/s1600/TRiface.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="225" src="https://1.bp.blogspot.com/-yxrrnTkfJok/WGT5jmxBN5I/AAAAAAAAAr4/Dm4Xtca_1qUkkYXUKvVFSN8e65U3VoVzgCLcB/s400/TRiface.jpg" width="400" /></a></div>
<div align="center" lang="zxx" style="margin-bottom: 0cm;">
<i>TR Systems
Interface</i></div>
</div>
<div style="text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://4.bp.blogspot.com/-BquQ5E5uHw8/WGT5hj8EFcI/AAAAAAAAAr0/IoaXiuO8Q1oFUt0LUnJ6yKMCIbLI6r5NACLcB/s1600/Froiface.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="225" src="https://4.bp.blogspot.com/-BquQ5E5uHw8/WGT5hj8EFcI/AAAAAAAAAr0/IoaXiuO8Q1oFUt0LUnJ6yKMCIbLI6r5NACLcB/s400/Froiface.jpg" width="400" /></a></div>
<div align="center" lang="zxx" style="margin-bottom: 0cm;">
<i>Frobisher
</i><i>TAR-3 </i><i>Interface</i></div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br /></div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
Both the RM15 and TR
machines have a similar interface style, with buttons for each
function. The TR machine seems to have taken a design lead from the
Geoscan machine, no doubt hoping that familiarity will translate into
ease of use. The Frobisher machine has a more minimalist style, with
5 buttons (duplicated, for left handers) controlling a menu system,
similar to that used by Bartington in their GRAD601. Ease of use is
subjective, and somewhat reliant on familiarity, but some comments
can be made.</div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
<br />
</div>
<div lang="zxx" style="margin-bottom: 0cm; text-align: justify;">
The Geoscan machine is
probably the easiest to use. The TR Systems meter works in much the
same way, but has an annoying feature where instead of beeping once
when a reading is taken, it will beep when it is starting to take the
reading and beep a second time when it is finished. If you take the
probes out too early, before the second beep, it will complain
furiously, saying something about checking the probes, when you know
it is because you took the probes out too early, and you have to wait
several seconds before it will allow you to continue. I gather that
this 'feature' is due to listening to feedback from users who really
should not have been listened to. The Frobisher, lacking the
dedicated buttons for each function, is probably the least intuitive,
and you will probably need the manual at hand the first few times you
use it, until you get used to it. Training is available though. There
are inconsistencies with the beeps to record a reading, so at the end
of line beep, there is a pause and a further beep which may
incorrectly suggest that another reading hasn't been taken, and when
you are retaking a reading, there is no beep to say it has been
taken. The other strange design decision relates to the end of the
grid. It will take 20 seconds to write out the readings to its
storage, and then turn itself off, cancelling out the speed increase
afforded by the ergonomic design. Hopefully some of these issues will
be resolved with firmware updates.</div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div lang="zxx" style="margin-bottom: 0cm;">
<b>Verdict: </b>1st –
Geoscan, 2nd – TR Systems, 3rd - Frobisher</div>
<br />
<br />
<br />
<div lang="zxx" style="margin-bottom: 0cm;">
<b>Ergonomics</b></div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
A big part
of the 'experience' of doing an earth resistance survey is lugging
the machine around the survey area, over and over again, so how your
equipment handles is of great importance. A common criticism of
equipment like this is the effect it has on someone with a bad back,
both because of the weight of the equipment, and because the height
of the bar which you hold on to can make you stoop somewhat. With
that in mind, here is a table with some statistics on the three
machines.</div>
<div lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<table cellpadding="6" cellspacing="0" style="width: 100%px;">
<colgroup><col width="85*"></col>
<col width="85*"></col>
<col width="85*"></col>
</colgroup><tbody>
<tr valign="top">
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: none; border-top: 1px solid #000000; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0cm; padding-top: 0.1cm;" width="33%">
<div lang="zxx">
<b>Machine</b></div>
</td>
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: none; border-top: 1px solid #000000; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0cm; padding-top: 0.1cm;" width="33%">
<div lang="zxx">
<b>Weight (sans cables)</b></div>
</td>
<td style="border: 1px solid #000000; padding: 0.1cm;" width="33%">
<div lang="zxx">
<b>Bar Height</b></div>
</td>
</tr>
<tr valign="top">
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: none; border-top: none; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0cm; padding-top: 0cm;" width="33%">
<div lang="zxx">
Geoscan RM15</div>
</td>
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: none; border-top: none; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0cm; padding-top: 0cm;" width="33%">
<div lang="zxx">
5.1Kg</div>
</td>
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: 1px solid #000000; border-top: none; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0.1cm; padding-top: 0cm;" width="33%">
<div lang="zxx">
93cm</div>
</td>
</tr>
<tr valign="top">
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: none; border-top: none; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0cm; padding-top: 0cm;" width="33%">
<div lang="zxx">
TR Systems</div>
</td>
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: none; border-top: none; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0cm; padding-top: 0cm;" width="33%">
<div lang="zxx">
4.4Kg</div>
</td>
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: 1px solid #000000; border-top: none; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0.1cm; padding-top: 0cm;" width="33%">
<div lang="zxx">
93cm</div>
</td>
</tr>
<tr valign="top">
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: none; border-top: none; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0cm; padding-top: 0cm;" width="33%">
<div lang="zxx">
Frobisher TAR-3</div>
</td>
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: none; border-top: none; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0cm; padding-top: 0cm;" width="33%">
<div lang="zxx">
2.8Kg</div>
</td>
<td style="border-bottom: 1px solid #000000; border-left: 1px solid #000000; border-right: 1px solid #000000; border-top: none; padding-bottom: 0.1cm; padding-left: 0.1cm; padding-right: 0.1cm; padding-top: 0cm;" width="33%">
<div lang="zxx">
105cm</div>
</td>
</tr>
</tbody></table>
<div lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
As you can
see, the Frobisher is much lighter and has a higher bar than the
other two. My volunteer, Stuart, who has a history of back problems,
reported that the Frobisher was his favourite. Another beneficial
side effect of a ligher machine is the ability to move it quicker,
meaning the survey area is covered quicker. Frobisher can supply
whatever bar height required on ordering, including a childrens size
frame (40cm-130cm).</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<b>Verdict</b>:
1st - Frobisher, 2nd – TR Systems, 3rd – Geoscan</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<b>Hardware
Options</b></div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
The biggest
selling point of the Geoscan RM85 has a built-in multiplexer, which
used to be a separate add-on to the RM15, so parallel and deeper
readings can be taken at the same time using the adjustable probe
frame (an additional option). The RM85 also has an option of GPS
recording if you are into using point clouds.
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
The TR
systems meter had an optional tomography kit for doing manual ERT
surveys and producing pseudosections using the free version of
RES3DINV.</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
The
Frobisher machine, being new, has yet to accumulate the same level of
hardware options as the other machines, but one very useful feature
is that the fixed probe cable is easily extendable, meaning more
grids can be surveyed without moving the fixed probes. The
manufacturer has mentioned that the cable could potentially be done
away with entirely, with an entirely separate transmitter, which
means very large areas could be done without moving the fixed probes,
so faster surveys and no edge matching in software required. A wenner
bar is available, and a tomography kit is in production.</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<b>Verdict:</b>
It really depends what you find useful!</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<br />
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<b>Battery</b></div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
While I
can't compare battery life for each machine, I can comment on how
easy it is to change batteries.</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
The Geoscan
RM15 and RM85 have an internal battery pack of standard batteries
(normal or rechargable). The unit needs to be unscrewed to replace
the batteries, but it is possible to do this in the field.</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
The TR
Systems meter has two plastic trays that slot into the side of the
machine, so batteries (9V, standard or rechargable) can be easily
changed in the field.</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
The
Frobisher TAR-3 has an internal rechargable battery pack that is not
user accessible. If something goes wrong with the battery, the unit
must be returned to the manufacturer. It is charged via a USB
connector, so can be charged in the field using a car charger, or
anything that could charge a phone.</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<b>Verdict:</b>
1st – TR Systems, 2nd – Geoscan, 3rd - Frobisher</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<b>Downloading
Data</b></div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
The RM15 and
TR systems meter download via an old 9 pin serial connector, so you
would need a serial to USB converter or card to download the data.
Fortunately, the replacement for the RM15, the RM85, has now been
changed to a USB connector that mimics a serial port, no additional
hardware needed. The Frobisher TAR-3 stores data on an SD card that
can be read with any card reader, so getting the data onto your
computer is much faster.</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<b>Verdict:</b>
1st – Frobisher, 2nd – Geoscan, 3rd – TR Systems</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<b>Data
Quality</b></div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
The test
site was a park through which ran a Roman road. The park is
surrounded by buildings, which was an opportunity to see how the
three machines were affected by AC interference. The same fixed probe
location (0.5m apart) was used for each of the three surveys. The
area had been previously surveyed using GPR, and the road is visible
in the timeslices starting at about 30cm down, along with some land
drains or utilities. The surface is known to be made of flint, and
the local geology is on the boundary between Folkestone Formation
sandstone and Lower Greensand.</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
</div>
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
<br />
</div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://3.bp.blogspot.com/-hgDzHi5Zcu0/WGT6MhgtkmI/AAAAAAAAAsA/fp62EMAnhP4i0lZfP9QyGddOXhMfD_1GACLcB/s1600/hassocks0616-12_5ns.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="391" src="https://3.bp.blogspot.com/-hgDzHi5Zcu0/WGT6MhgtkmI/AAAAAAAAAsA/fp62EMAnhP4i0lZfP9QyGddOXhMfD_1GACLcB/s400/hassocks0616-12_5ns.png" width="400" /></a></div>
<br />
<div align="justify" lang="zxx" style="margin-bottom: 0cm;">
The GPR grid
shown above is 30x30m, and the earth resistance test grid occupies
the top-left 20x20m of that area. The results, shown below were
processed in Snuffler with no filters applied. The display bounds
were set to 95% of the readings around the median. There isn't much
evidence of noise on any of the three images, and they seem broadly
consistent with eachother.</div>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-7b3zRauwjF0/WGT6ah4VjWI/AAAAAAAAAsE/g6eWopk_jHMjRqQPPOPONz7NrkqCUiBXQCLcB/s1600/RM15datPrev.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="https://1.bp.blogspot.com/-7b3zRauwjF0/WGT6ah4VjWI/AAAAAAAAAsE/g6eWopk_jHMjRqQPPOPONz7NrkqCUiBXQCLcB/s320/RM15datPrev.png" width="320" /></a></div>
<div align="center" lang="zxx" style="margin-bottom: 0cm;">
<i>Geoscan
RM15</i></div>
</div>
<div lang="zxx" style="margin-bottom: 0cm;">
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<i>TR Systems</i></div>
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<a href="https://2.bp.blogspot.com/-DQ7h_lBGP84/WGT6rRGsryI/AAAAAAAAAsQ/w4OvJ7Y5Y_Ew1CGin7XM5omR18sPToZJwCLcB/s1600/TAR3DATA1Prev.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="https://2.bp.blogspot.com/-DQ7h_lBGP84/WGT6rRGsryI/AAAAAAAAAsQ/w4OvJ7Y5Y_Ew1CGin7XM5omR18sPToZJwCLcB/s320/TAR3DATA1Prev.png" width="320" /></a></div>
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<i>Frobisher
TAR-3</i></div>
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<b>Verdict:</b> Not much to choose between them, make up your own
mind!</div>
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<b>Price</b></div>
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When I
bought my TR systems meter, many years ago, the price was £1200.
Inflation would make that about £1800. At the time of writing, the
Frobisher TAR-3 is £1844 (including a days training), not very
different from the TR Systems meter, and aimed at the same budget
conscious market. I'm not absolutely sure of the price of the
currently Geoscan RM85, but I have been told the basic machine £5000,
with the multi-probe array another £1500.</div>
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<b>Verdict:</b>
Joint 1st – TR systems, Frobisher, 3rd – Geoscan</div>
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<b>Conclusion</b></div>
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Given that
the TR Systems meter is not currently available, that leaves us with
the Geoscan and Frobisher machines. If you want the multiplexer
option, then get the RM85, otherwise the lower cost and lighter
Frobisher machine will save your back and bank balance.</div>
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David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-22073371042712723932016-10-29T21:38:00.001+01:002016-10-29T21:38:39.804+01:00Latest Results: Chichester<div style="text-align: justify;">
Following on from <a href="http://geophyswithsnuffler.blogspot.co.uk/2015/09/latest-results-chichester.html">last year's very successful radar survey in Chichester</a>, I went back for another week of the same, this time around the area of the Cathedral in the south-west quadrant of the city. <a href="http://www.cdas.info/">Chichester & District Archaeological Society</a> had already found a lot in the area using earth resistance and excavation, so the radar didn't show a lot that was new, just in slightly better definition. There wasn't a lot around the cathedral itself, so the area has probably had any Roman remains there thoroughly removed, but there was around the Deanery and Bishop's Palace. The garden of the Deanery contains the old medieval (or post-medieval) Deanery, and the the area in front of the Bishop's Palace contains a Roman building and the medieval hall that was the old Bishop's palace.</div>
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<a href="https://3.bp.blogspot.com/-ApU6LWNpedI/WBUGhnx6F9I/AAAAAAAAAqk/ZTb7kYVSq6U6DPuYl_a3Octto67KEkD7gCLcB/s1600/ce16interp.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="253" src="https://3.bp.blogspot.com/-ApU6LWNpedI/WBUGhnx6F9I/AAAAAAAAAqk/ZTb7kYVSq6U6DPuYl_a3Octto67KEkD7gCLcB/s400/ce16interp.jpg" width="400" /></a></div>
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<i>The old Deanery in the garden of the current Deanery</i></div>
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<i>Click for larger image</i></div>
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<a href="https://1.bp.blogspot.com/-oBZLu6GmIYI/WBUGPO76g9I/AAAAAAAAAqg/MemfatmgT5QmIgRFGOsQvMPwG99bQvvqwCLcB/s1600/cc16interp.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="https://1.bp.blogspot.com/-oBZLu6GmIYI/WBUGPO76g9I/AAAAAAAAAqg/MemfatmgT5QmIgRFGOsQvMPwG99bQvvqwCLcB/s400/cc16interp.jpg" width="357" /></a></div>
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<i>Roman building (green) and medieval Bishop's Palace (orange)</i></div>
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<i>Click for larger image</i></div>
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I also went back to Priory Park to look again at the third Roman building (in green, within the lighter survey area) found near the cricket pitch. It has suffered greatly from robbing, not least by the Saxons, who seem to have used some of the stone in their sunken floor buildings, two of which appear (in purple) in the higher resolution re-survey of this area.<br />
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<a href="https://2.bp.blogspot.com/-GIXCwmhLiFo/WBUHYO5rNnI/AAAAAAAAAqw/DzQPp8b4tqQ_Sy0U-p99J-zGbgj1BwW0wCLcB/s1600/cp16interp.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="225" src="https://2.bp.blogspot.com/-GIXCwmhLiFo/WBUHYO5rNnI/AAAAAAAAAqw/DzQPp8b4tqQ_Sy0U-p99J-zGbgj1BwW0wCLcB/s400/cp16interp.jpg" width="400" /></a></div>
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<i>Priory Park survey. Click for larger image.</i></div>
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I'll be giving a talk on the results from both years for CDAS on the 22nd of February 2017 at 7:30pm in the cinema of the New Park Centre, New
Park Road, Chichester.<br />
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<br />David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-60757622204652898012016-10-04T08:10:00.000+01:002016-11-27T20:39:39.308+00:00More on Processing UK Environment Agency LIDAR Data <div style="text-align: justify;">
Since I found that <a href="http://geophyswithsnuffler.blogspot.co.uk/2015/11/processing-uk-environment-agency-lidar.html">my last blog post on displaying Environment Agency LIDAR DEMs</a> has become the most ever viewed blog post that I have written (popular subject apparently), I've been thinking of writing a followup, having learned a few new things. One of the main problems with dealing with all this LIDAR data is speed. First, getting the data to a state that is useful takes a lot of processing, which can be solved by automating the process using some python scripts I wrote. Second, the draw speed on the screen in QGIS can be solved using <a href="https://docs.qgis.org/2.8/en/docs/training_manual/rasters/data_manipulation.html#basic-fa-create-a-virtual-raster">Virtual Raster Tables</a> and <a href="http://www.northrivergeographic.com/archives/pyramid-layers-qgis-arcgis">Pyramids</a>. This tutorial will assume that you are using the <a href="https://trac.osgeo.org/osgeo4w/">OSGeo4W</a> package on windows, with QGIS, python and OSGeo4W Shell options installed, but much of it may be transferable to other setups.</div>
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I'll start by throwing some python code at you for processing the data, and then explain a bit about what it does and how to run it. Put this code in a file somewhere called <b>demimport.py</b><br />
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<span style="color: #cc0000;"><span style="font-family: "courier new" , "courier" , monospace;">#!/usr/bin/env python<br /><br />import sys<br />import zipfile<br />import os<br /><br />impdir='e:\\data\\gis\\dem\\import'<br />expdir='e:\\data\\gis\\dem'<br /><br />def unzipfile(filename,exportto):<br /> with zipfile.ZipFile(filename, "r") as z:<br /> z.extractall(exportto)<br /><br />def main( argv=None ):<br /> # Part 1, unzip the data and merge the contents into one file, deleting the intermediate files on completion<br /> for file in os.listdir(impdir):<br /> if file.endswith(".zip"):<br /> # Work out the filenames we are using<br /> print "File: ", file<br /> stubname = file[:-4]<br /> print "Stubname: ", stubname<br /> outdir = expdir + "\\" + stubname<br /> print "outdir: ", outdir<br /> impfile = impdir + "\\" + file<br /> print "impfile: ", impfile<br /> demname = outdir + "\\" + stubname + ".asc"<br /> print "demname: ", demname<br /><br /> # First, deal with the zip file<br /> if not os.path.exists(outdir):<br /> os.mkdir(outdir)<br /> unzipfile(impfile,outdir)<br /> os.remove(impfile)<br /><br /> # Now get a list of files in the created directory and construct the script to merge them<br /> script = "gdal_merge.bat -n -9999 -a_nodata -9999 -of GTiff -o " + demname<br /> for file2 in os.listdir(outdir):<br /> if file2.endswith(".asc") and not file2.startswith("LIDAR-DTM"):<br /> script += " " + outdir + "\\" + file2<br /> print "script: ", script<br /> os.system(script)<br /> for file2 in os.listdir(outdir):<br /> if file2.endswith(".asc") and not file2.startswith("LIDAR-DTM"):<br /> os.remove(outdir + "\\" + file2)<br /><br /> # Part 2, Create hillshade files from the files created in part 1<br /> for f in os.listdir(expdir):<br /> if os.path.isdir(os.path.join(expdir, f)) and f.startswith("LIDAR-DTM"):<br /> # Work out the filenames we are using<br /> stubname = expdir + "\\" + f + "\\" + f<br /> print "Stubname: ", stubname<br /> demname = stubname + ".asc"<br /> print "demname: ", demname<br /> hsname = stubname + "-HS.asc"<br /> print "hsname: ", hsname<br /> hs2name = stubname + "-HS2.asc"<br /> print "hs2name: ", hs2name<br /><br /> if os.path.exists(demname):<br /> if not os.path.exists(hsname):<br /> # Now create the hillshade<br /> script = "gdaldem hillshade " + demname + " " + hsname + " -z 1.0 -s 1.0 -az 315.0 -alt 45.0 -compute_edges -of GTiff"<br /> os.system(script)<br /> if not os.path.exists(hs2name):<br /> # Now create the second hillshade<br /> script = "gdaldem hillshade " + demname + " " + hs2name + " -z 1.0 -s 1.0 -az 45.0 -alt 45.0 -compute_edges -of GTiff"<br /> os.system(script)<br /><br />if __name__ == '__main__':<br /> sys.exit(main())</span></span></div>
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You will see near the top of this script two directories called <b>impdir</b> and <b>expdir</b>. <b>impdir</b> is the directory where you dump the zipfiles you download from the environment agency website. <b>expdir</b> is the directory where the script will output the resulting data. Change these to whatever directory structure you wish to use on your computer. The script will merge the contents of each zip file into a single file and then create two different hillshades from that data. More on the hillshades later. It automates most of what I described in my last blog post, all apart from setting the style data in QGIS. You can run the script by opening <b>OSGeo4W Shell</b>, changing directory to where you have saved the python file and typing <b>@python demimport.py</b>.</div>
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The next bit is about speeding up the data display in QGIS itself, using the aforementioned Virtual Raster Tables (hereafter, VRTs) and Pyramids. First, VRTs. Imagine you have 100 LIDAR tiles active for display in QGIS. Each time you zoom or move the display, it has to read them all to see which it can display in the area you are viewing at the time, which obviously means a lot of slow reading from your hard disk (assuming you still use those). A VRT acts as an index file for your 100 LIDAR tiles, so QGIS only has to look in one place to find out what it needs to display, and then only has to open the tiles that it requires to fill the area you are viewing, so everything displays much quicker. Pyramids speed things up in a different way. Imagine you are quite zoomed out, looking at a wide area of LIDAR data. QGIS would normally have to read the whole of each file and reduce it in size to fit into the small area that the tile would be displayed in. Creating a pyramid does this process ahead of time, so it takes the original image, compresses ito to a quarter of its size, then does that again and again and saves all that in a pyramid file, so when you are zoomed out, rather than reading the entirity of the original data, it will read the pre-compressed data suitable to your zoom level, reducing the amount it has to read from your hard disk and speeding up the display process. Those are the concepts behind it, now for the code that actually does it. Put this code in a file called <b>makevrt.py</b></div>
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<span style="color: #cc0000;"><span style="font-family: "courier new" , "courier" , monospace;">#!/usr/bin/env python<br /><br />import sys<br />import os<br /><br /><br /><br />def main( argv=None ):<br /> # definitions for the vrt we want to create, this changes<br /> resolution = "2M"</span></span><br />
<span style="color: #cc0000;"><span style="font-family: "courier new" , "courier" , monospace;"> <span style="color: #cc0000;"><span style="font-family: "courier new" , "courier" , monospace;"> expdir = 'e:\\data\\gis\\dem'</span></span></span></span><br />
<span style="color: #cc0000;"><span style="font-family: "courier new" , "courier" , monospace;"> inputareas = ["ST","SY","SS","SX"]<br /><br /> # File and directory names, this doesn't change<br /> ldtm = "LIDAR-DTM-"<br /> ext = ".vrt"<br /> vrtnamestub = "VRT" + "\\" + ldtm + resolution<br /> types = [ "", "-HS", "-HS2" ]</span></span><span style="color: #cc0000;"><span style="font-family: "courier new" , "courier" , monospace;"><span style="color: #cc0000;"><span style="font-family: "courier new" , "courier" , monospace;"> listname = expdir + "\\filelist.txt"</span></span></span></span><br />
<span style="color: #cc0000;"><span style="font-family: "courier new" , "courier" , monospace;"><span style="color: #cc0000;"><span style="font-family: "courier new" , "courier" , monospace;"><br /></span></span> for type in types :<br /> for ia in inputareas:<br /> vrtname = expdir + "\\" + vrtnamestub + "-" + ia + type + ext<br /> pyramidname = vrtname + ".ovr"<br /><br /> if not os.path.exists(vrtname):<br /><span style="font-family: "courier new" , "courier" , monospace;"> script = "gdalbuildvrt -input_file_list " + listname + " " + vrtname<br /><br /> base = ldtm + resolution + "-" + ia<br /> base2 = expdir + "\\" + base<br /> fp = open(listname,"w")<br /> for dir in os.listdir(expdir):<br /> if dir.startswith(base):<br /> fp.write(expdir + "\\" + dir + "\\" + dir + type + ".asc\n")<br /> fp.close()</span><br /><br /> print "script: " + script<br /> os.system(script)<br /><br /> if os.path.exists(vrtname) and not os.path.exists(pyramidname): <br /> print "processing: " + vrtname<br /> # Now create the pyramids<br /> script = "gdaladdo -r CUBIC -ro " + vrtname + " 2 4 8 16 32 64"<br /> os.system(script)<br /><br /><br />if __name__ == '__main__':<br /> sys.exit(main())</span></span><br />
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You can run the script by opening OSGeo4W Shell, changing directory to
where you have saved the python file and typing <b>@python makevrt.py</b>. Again, there are some changes you will need to make at the top of the file. <b>resolution</b> is the type of data you are dealing with. You can download 2M, 1M, 50CM or 25CM data from the Environment Agency website, this script will only do one at a time. <b>expdir</b> should be the same as expdir from the first script. You will also need to create a subdirectory off of that called 'VRT', which is where this script creates its new files. <b>inputareas</b> is a list of <a href="https://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid#Grid_letters">Ordnance Survey Grid Letters</a> that the script will generate VRTs for. It will generate one set of files for each grid letter, you have to tell it which ones to do. After that, you can load the newly created VRT files into QGIS using the <b>Add Raster Layer</b> button and style them as per <a href="http://geophyswithsnuffler.blogspot.co.uk/2015/11/processing-uk-environment-agency-lidar.html">my original blog post</a>.</div>
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Now back to those two different hillshades I mentioned. Why two different hillshades? If you imagine a hillshade a shining a light from a particular angle to create highlights and shadows, a linear feature running in the same direction as the direction of the light will not show up very well, so I've created a second hillshade with the light coming in at a 90 degree angle to the first hillshade. You can see the difference below.</div>
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<a href="https://3.bp.blogspot.com/-2FOPrPqCNqI/V_NRyX9aTZI/AAAAAAAAApI/wq4gQqyd_pUJXdy-rrK2BZm-vc5HBAleACLcB/s1600/iow3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="253" src="https://3.bp.blogspot.com/-2FOPrPqCNqI/V_NRyX9aTZI/AAAAAAAAApI/wq4gQqyd_pUJXdy-rrK2BZm-vc5HBAleACLcB/s400/iow3.jpg" width="400" /></a></div>
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<i> First hillshade. Click for larger image.</i></div>
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<a href="https://1.bp.blogspot.com/-FKRsOJC5ifI/V_NSRB7XFYI/AAAAAAAAApM/eDVd67CXDVs8mu522pf6PPd_PD79zeuLgCLcB/s1600/iow4.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="253" src="https://1.bp.blogspot.com/-FKRsOJC5ifI/V_NSRB7XFYI/AAAAAAAAApM/eDVd67CXDVs8mu522pf6PPd_PD79zeuLgCLcB/s400/iow4.jpg" width="400" /></a></div>
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<i> Second hillshade. Click for larger image.</i></div>
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If you click on the images and look at the highlighted feature, a possible new (unconfirmed) Roman road on the Isle of Wight, you will see that it is much clearer in the second image compared to the first. My script generated the hillshades with light coming in from the north-east in the first image, which is parallel to the road feature, and from the north-west in the second image, which is perpendicular to the road feature, showing it up better.</div>
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<br />David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-13236176705428130882016-08-14T13:54:00.000+01:002016-08-14T13:54:49.168+01:00Roman Roads conference in Portsmouth<div style="text-align: justify;">
Many of you who know me know that my personal research project, which I have been working on for the last few years is Roman Roads and roadside settlements. I've been asked to speak on the subject at a conference on the subject of Roman roads in memory of Ivan Margary, the most famous of all Roman road researchers in Britain. I'll be doing two talks (that's a full Bonsall for you geophysicists out there), the first on the subject of Roman roads research in the county of Sussex, Ivan's original stomping ground, and the second talk on the use of geophysics for finding Roman roads. The conference is a two day conference on the 3rd and 4th of September 2016 at Portsmouth University. The website for the organisers of the conference is <a href="http://www.romanroads.org/">here</a>.</div>
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David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-43467706473237736612016-04-07T19:40:00.000+01:002016-04-08T04:46:03.053+01:00Snuffler version 1.2: The radar experiment<div style="text-align: justify;">
It's time for a new version of Snuffler. I've upgraded from visual studio 2005 to 2015 and changed drawing of custom graphics in dialog boxes, e.g. in the Display Settings dialog, so let me know if you get any strange new problems. If you get an error starting up the new version of Snuffler, you will probably need to run the redist exe that comes in the same zip file.<br />
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The main feature added this time is functionality for the display of radar data. Not much mind you, very little in fact. It all started <a href="http://geophyswithsnuffler.blogspot.co.uk/2013/05/trying-out-ground-penetrating-radar.html">back when I got my radar</a>. I also got a copy of ReflexW, and I'm happy enough using that, but having written Snuffler, I found I was not completely happy with the way radar data is traditionally displayed, and wanted to have a go at writing a display process to see if I could do better. Apart from basic training on how to use ReflexW, I have no formal training in GPR processing theory. Thousands of papers on the subject have passed me by, and I wouldn't really know where to start looking. Some of what I'm doing here is re-inventing the wheel, but I still wanted to have a go at it, despite going in blind. The new functionality I have added to Snuffler is not intended to be a useful GPR processing system, it is very far from that. It is intended to scratch an itch I had regarding GPR display methods and learn something for myself along the way.</div>
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For those of you who are not completely familiar with how radar data is displayed, here is a bit of history to bring you up to speed. Apologies if you already know this stuff. Click on any of the images to show a larger version. Unlike for earth resistance and magnetometry, which give a single reading at any point, radar will give you a vertical trace going through the ground. The resulting wave recorded at a single point in horizontal space is known as an A-Scan, and an example is shown below.</div>
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<i>A-Scan</i></div>
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The top of this wave is at the ground surface and goes down into the ground. The dotted red line is an amplitude (signal strength) of zero, so as the wave extends further from that line, the more signal is being reflected and the greater the strength of signal. You tend to get a greater reflection at the surface, as less and less energy penetrates further into the ground as you go deeper. So that's a single point on the ground. If you record a line of these and string them together, this is known as a B-Scan. An example of which is shown below.</div>
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<a href="https://4.bp.blogspot.com/-7I8nIp8hhOM/VvYJuJmeTPI/AAAAAAAAAjI/_ST9LpHTpxQYXlDgSS42fHrvE1HOIU9pQ/s1600/A-scans-to-B-scan.print.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="166" src="https://4.bp.blogspot.com/-7I8nIp8hhOM/VvYJuJmeTPI/AAAAAAAAAjI/_ST9LpHTpxQYXlDgSS42fHrvE1HOIU9pQ/s400/A-scans-to-B-scan.print.jpg" width="400" /></a></div>
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<i>B-Scan, historical display method</i></div>
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This is how B-Scans used to be displayed in the early days of computing, when everything was monochrome. The A-Scans where arranged in a line, and the area under the curve of the wave to the right of the zero line was filled with black to create contrast for high amplitude areas. This display method is the equivalent of the dot-density plot for earth resistance, when technology was similarly limited to monochrome, and thankfully isn't used much any more. The progression from this, when shades of grey became available, was to assign white to a negative amplitude (left of the zero line), through the shades of grey to mid grey at the zero line and on to black at a high positive amplitude (right of the zero line). The wave itself was no longer drawn, just the grey appropriate to the amplitude. This would give us the common method of B-Scan display used today, as shown in the example below.</div>
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<a href="https://3.bp.blogspot.com/-j8qobNjYrkU/VvYL8qMeTfI/AAAAAAAAAjU/sGZVhjxWSqIQpaV0_GTqp5eCbhJ_W4rjQ/s1600/wiggle.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="68" src="https://3.bp.blogspot.com/-j8qobNjYrkU/VvYL8qMeTfI/AAAAAAAAAjU/sGZVhjxWSqIQpaV0_GTqp5eCbhJ_W4rjQ/s400/wiggle.png" width="400" /> </a></div>
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B-Scan, current display method </div>
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Thus ends the history lesson. The example B-scan above, which I will use as an example throughout the rest of this blog post is from a town called Ewell. During the excavation by the Surrey Archaeological Society of a Roman road called Stane Street, I went to an adjacent modern road and walked along the pavement, crossing Stane Street. The curving feature in the middle is what I hope is the camber of the Roman road.</div>
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So what can you do with Snuffler? To get the data into Snuffler, there is a SEGY file import. SEGY is a common standard for sharing GPR data that can be used by many pieces of GPR software. Currently, Snuffler can currently only import a subset of this, the '2-byte, two's complement integer' type output by ReflexW. If you are trying this out and can't get Snuffler to import your file, zip it up and email it to me and I will get it working. The example above has already been processed in ReflexW, with static correction, background removal, gain and bandpass filters applied; basic stuff that Snuffler cannot do.</div>
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The standard method of display, as shown above, is the first thing you will see when you open the file in Snuffler, and here I want to discuss why I have a problem with this display method. There are two pieces of information that an image like this can tell you, amplitude and phase. It will show you both, but it will show you neither very well.</div>
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Amplitude is the strength of the wave. You can easily see a broad band across the top of the image with higher amplitude shown as lines of black and white rather than the grey of low amplitude. In a normal earth resistance plot in Snuffler, the scale might go from black as a low reading to white as a high reading. With GPR, both black and white are high amplitude, cutting the palette in half as far as contrast is concerned. It also doesn't help that the shades representing the high points on the wave only appear briefly before plunging back towards the zero line, making comparison of amplitude even more difficult. You can't even concentrate the display range at a certain amplitude to increase contrast without losing the other (negative) half of your data. The solution to this is quite common, but is not often applied to B-Scan data, the <i>envelope</i>. The envelope basically takes absolute value of the amplitude (makes everything positive) and fills in the gaps between the waves. This is normally done using a <a href="https://en.wikipedia.org/wiki/Hilbert_transform">Hilbert Transform</a>, but since my maths isn't that great, I literally took the absolute values and filled in the gaps instead. The result looks something like this. This, and the other display methods shown hereare not filters in the sense that they change the data, they are on the fly display methods that leave the data alone.</div>
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<a href="https://3.bp.blogspot.com/-ktPyAgyMglU/VvYT-zjdLtI/AAAAAAAAAjk/AFX9SMEzokkQdj7f4o6pkpktCWQTtWGOQ/s1600/amp1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="68" src="https://3.bp.blogspot.com/-ktPyAgyMglU/VvYT-zjdLtI/AAAAAAAAAjk/AFX9SMEzokkQdj7f4o6pkpktCWQTtWGOQ/s400/amp1.png" width="400" /></a></div>
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<i>"Envelope" data</i></div>
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Now black is low amplitude and white is high amplitude. We have completely lost the phase information (more on that in a bit), but we can see the amplitude a lot better. We can still improve on this.</div>
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<a href="https://4.bp.blogspot.com/-wKpwVnI7CTs/VvYUxl4vpuI/AAAAAAAAAjo/3VHze9TKc8M9fm10Bq0-qeoyuahkKET3A/s1600/ampgraph.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="178" src="https://4.bp.blogspot.com/-wKpwVnI7CTs/VvYUxl4vpuI/AAAAAAAAAjo/3VHze9TKc8M9fm10Bq0-qeoyuahkKET3A/s400/ampgraph.png" width="400" /></a></div>
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<i> Graph of amplitude data</i></div>
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The graph shows the amplitude on the X axis and the number of readings with that amplitude on the Y axis. If we move the low bound very slightly so the majority of the low readings are ignored and change the palette usage to non-linear, we can get better contrast. A non-linear palette is where instead of a shade of grey being assigned to an amplitude range, it is assigned to an equal number of readings with a similar amplitude. The result looks like this.</div>
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<a href="https://1.bp.blogspot.com/-xtEKwZgevhY/VvYV6qLFaKI/AAAAAAAAAj4/dS8ozbtxxC0baQ4-h4Rki8kY0_PGSzGAQ/s1600/amp2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="68" src="https://1.bp.blogspot.com/-xtEKwZgevhY/VvYV6qLFaKI/AAAAAAAAAj4/dS8ozbtxxC0baQ4-h4Rki8kY0_PGSzGAQ/s400/amp2.png" width="400" /></a></div>
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<i>"Envelope" data with better contrast</i></div>
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So that's amplitude, what about phase? In simplified terms, a wave with a single frequency, given no obstacles, will have the same wavelength all along its length. There would be the same number of samples between the peaks of the wave. When the wave hits an obstacle, or in the case or GPR, hits a material with a different dielectric potential, the wavelength is temporarily shortened at the point of the interface before continuing, thus the phase of the wave changes. This effect is what produces the nice curve of the Roman road camber in our example. So what is the problem with the standard display method here? While it is easy to see the phase when the amplitude is high, the bottom of the image is a sea of grey with no contrast, rendering the phase there all but invisible. The common solution to this, often used in the oil industry where they go to very great depths, is something called <i>Automatic Gain Control</i>. For each line at a depth along the B-Scan, an average is taken in a time window around that line and the values along the line are changed to reflect the average. The effect of this is to remove the high amplitude bias at the top of the image and flatten it out, losing the amplitude information. This produced something like this.</div>
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<a href="https://3.bp.blogspot.com/-B3rVbk-Wnng/VvYZM4HrK5I/AAAAAAAAAkE/MZMW9JYOSEIq59ugEBXKY3qNX8Iwlx-Dw/s1600/agc1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="68" src="https://3.bp.blogspot.com/-B3rVbk-Wnng/VvYZM4HrK5I/AAAAAAAAAkE/MZMW9JYOSEIq59ugEBXKY3qNX8Iwlx-Dw/s400/agc1.png" width="400" /></a></div>
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<i>Automatic Gain Control</i></div>
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Now you can see the lines all the way to the bottom, but we can still improve on this, as there isn't much contrast.</div>
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<a href="https://4.bp.blogspot.com/-Or--MVSxLlY/VvYZiJYSg6I/AAAAAAAAAkI/aE8lnNVmB1wE-uJQBH-fJTYIst9qti_sQ/s1600/agcgraph.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="178" src="https://4.bp.blogspot.com/-Or--MVSxLlY/VvYZiJYSg6I/AAAAAAAAAkI/aE8lnNVmB1wE-uJQBH-fJTYIst9qti_sQ/s400/agcgraph.png" width="400" /></a></div>
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<i>Graph of AGC data</i></div>
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If we change the display bounds to around the curve of the readings and use a non-linear display process as before, we can get a lot more contrast, resulting in a much clearer image as below.</div>
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<a href="https://3.bp.blogspot.com/-gnKxNE-L34A/VvYZ9sKkhWI/AAAAAAAAAkQ/2YUbOA7o4QgYObHtyGYw5ynkMyPlDrJoA/s1600/agc2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="68" src="https://3.bp.blogspot.com/-gnKxNE-L34A/VvYZ9sKkhWI/AAAAAAAAAkQ/2YUbOA7o4QgYObHtyGYw5ynkMyPlDrJoA/s400/agc2.png" width="400" /></a></div>
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<i>Automatic Gain Control with better contrast</i></div>
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So far, so standard. Here is something that is hopefully a little different, but someone else has probably thought of it already. With the "envelope" data above, the high amplitude features are visible near the surface, but what about features at depth that have a high amplitude compared to other areas at the same depth, but a low amplitude compared to the features at the surface. They are invisible. If we apply automatic gain control followed by an envelope however, we get something like this.</div>
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<a href="https://1.bp.blogspot.com/-IhB7dWTl2Uc/VvYcTwDz17I/AAAAAAAAAkg/ylThQO4uY6UqgrUh-DecuomO8kDYM9cWA/s1600/apa1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="68" src="https://1.bp.blogspot.com/-IhB7dWTl2Uc/VvYcTwDz17I/AAAAAAAAAkg/ylThQO4uY6UqgrUh-DecuomO8kDYM9cWA/s400/apa1.png" width="400" /></a></div>
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<i>AGC plus envelope</i></div>
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The effect is to lose the absolute amplitude we had before and gain a relative amplitude showing the strongest features at each sample depth. Of course, we can adjust the display parameters to get a better contrast.</div>
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<a href="https://4.bp.blogspot.com/-FCRUnwN8AVE/VvYdJ8LnNfI/AAAAAAAAAko/YOszu6ZAdUQXGU52wIzbeYZIm3Uj-IwaA/s1600/apagraph.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="178" src="https://4.bp.blogspot.com/-FCRUnwN8AVE/VvYdJ8LnNfI/AAAAAAAAAko/YOszu6ZAdUQXGU52wIzbeYZIm3Uj-IwaA/s400/apagraph.png" width="400" /></a></div>
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<i>Graph of AGC plus envelope data</i></div>
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If we set the low display bound to exclude the low amplitude samples and use a non-linear palette, we get this.</div>
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<a href="https://2.bp.blogspot.com/-oaAv6ou7Q7A/VvYdvHeHT2I/AAAAAAAAAks/1dzHntnLLwgIffc9oG8M-CTT1R_gZQ2Vg/s1600/apa2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="68" src="https://2.bp.blogspot.com/-oaAv6ou7Q7A/VvYdvHeHT2I/AAAAAAAAAks/1dzHntnLLwgIffc9oG8M-CTT1R_gZQ2Vg/s400/apa2.png" width="400" /></a></div>
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<i>AGC plus envelope with better contrast</i></div>
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Now we can see the interesting features a lot clearer, including that interesting block to the left of Stane Street and Stane Street itself now shows as much more distinct than the rest of the material at that level. So we have three different display methods that are all better than the standard at doing their thing, but you need to look at all three to get the best picture, which is why most people stick with the standard display process that is a Jack of all trades but a master of none. Wouldn't it be great if you could see all three at once?</div>
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<a href="https://2.bp.blogspot.com/-wnxG9T0VEwY/VvYehKS66iI/AAAAAAAAAk0/vBpbmOlxdJkiDtrh7glocGXslpbYlca2g/s1600/finalimage.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="68" src="https://2.bp.blogspot.com/-wnxG9T0VEwY/VvYehKS66iI/AAAAAAAAAk0/vBpbmOlxdJkiDtrh7glocGXslpbYlca2g/s400/finalimage.png" width="400" /></a></div>
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<i>Channel merged image</i></div>
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Funky. Could you imagine scrolling through timeslices of that? It would be mindbending. Just like the <a href="http://geophyswithsnuffler.blogspot.co.uk/2013/01/version-11-of-snuffler-released.html">channel merging I did a few versions back</a>, this display method lets you view all three display methods in the same place. The "envelope" data is in the red channel, the automatic gain control in green and AGC plus envelope in blue. You lose some contrast having them all merged together, but the resulting image I think is far more useful than the standard display method that we are all used to. So there you go, itch scratched and funky GPR plots accomplished. I don't think I'll ever make Snuffler a fully functional GPR processing system, but hopefully this will be useful to someone out there. I may do time slices.</div>
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You can download this version of Snuffler <a href="http://www.sussexarch.org.uk/geophys/snuffler.html">in the usual place</a>.</div>
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David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com1tag:blogger.com,1999:blog-5157785897936147656.post-26937697615959613352016-01-03T14:32:00.000+00:002016-01-03T15:56:26.183+00:00It's talking Season Again<div style="text-align: justify;">
Winter is here, or not with these warm temperatures, so it is time for me to put down the geophys gear and do some talks.</div>
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The first will be for the <a href="http://www.eastbournearchaeology.org.uk/">Eastbourne Natural History and Archaeological Society</a>. It is at St Saviour’s Church Hall, Spencer Rd, Eastbourne on Friday 8th of January 2016 at 7:30pm. I'll be doing some geophysics for the society in 2016, so I've been asked to talk about the sort of things that geophysics can find by talking about the settlements along the Hardham to Pevensey Roman road, focussing on Barcombe.</div>
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The second is at <a href="http://media.wix.com/ugd/472ea5_4aceffeb0de34927a6ac7b906a31bdc2.pdf">this year's symposium</a>, run by the <a href="http://www.sussexarchaeology.org/">Sussex School of Archaeology</a>, on the subject of the <a href="http://geophyswithsnuffler.blogspot.co.uk/2015/09/latest-results-chichester.html">radar I did on Roman Chichester</a>. I'll hopefully be back in 2016 to do more of that, so there may well be further talks. The date for that talk is the 19th of March, 2016, at the Huxley Building, University of Brighton.</div>
David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com1tag:blogger.com,1999:blog-5157785897936147656.post-23966064107407482012015-11-08T21:09:00.000+00:002015-11-08T21:09:18.602+00:00Processing UK Environment Agency LIDAR Data Tutorial<div style="text-align: justify;">
Recently, the <a href="http://environment.data.gov.uk/ds/survey">Environment Agency has released its LIDAR data to the public</a>. This is not the first time that DEM (Digital Elevation Map) data has been released from free. Satellite based DEM data has been released by <a href="https://asterweb.jpl.nasa.gov/gdem.asp">ASTER</a> and <a href="http://www2.jpl.nasa.gov/srtm/">SRTM</a> (SRTM is less noisy), but those have a horizontal resolution of 30m, which is quite coarse. The EA data, which was collected using <a href="https://en.wikipedia.org/wiki/Lidar">LIDAR,</a> has a much higher horizontal resolution, but the downside is that there is gaps in the data. Several of my archaeology friends have asked me to do tutorial on how to display this data.</div>
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If you look at the website, zoom in and click on a map tile, you can see that you can download 6 different sets of data. There is DTM (Digital Terrain Map) and DSM (Digital Surface Map) data. The difference is that the DTM data has stuff like trees stripped, which makes it much more useful for archaeology than the DSM data. It also comes in 3 resolutions, 0.5m, 1m & 2m. The trade off is that there is less area convered for the higher resolutions. I would recommend starting with the 2m data and downloading 1m for the same area if you really need it.</div>
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When you download a file, you will get a zip file containing up to 100 <a href="https://en.wikipedia.org/wiki/Esri_grid">ASCII grid</a> files, each covering a 1km square. This is not a normal image, but a file containing the height data. which we must process using GIS software. This tutorial will cover processing that data using a popular open source GIS package called <a href="http://www.qgis.org/">QGIS</a>, which you can <a href="http://www.qgis.org/en/site/forusers/download.html">download for free</a> as a standalone application or as part of the OSGeo4w package. Here are the steps to follow.</div>
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If you haven't already got a project in QGIS, create a new one, setting the map projection to <a href="http://spatialreference.org/ref/epsg/7405/">OSGB36 (EPSG:7405)</a>.</div>
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Unzip the contents of each zip file, and place the contents of each one in a folder of their own, for example, if your zip file is called LIDAR-DTM-2M-TR14.zip, create a directory called LIDAR-DTM-2M-TR14 and copy the contents of the zip file in there.</div>
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You will notice there are a lot of files, and we don't really want to deal with them all individually, so we will merge them together into one giant ASCII grid, covering a 10x10km square. To do this in QGIS, go to the <b>Raster > Miscellaneous > Merge...</b> menu. Next to the <b>Input Files</b>, press the <b>Select...</b> button and select all of the asc files in a directory. You also need an <b>Output File</b> for the merged data, for which I use the name of the directory again, which must be followed by a file extension of .asc, for example LIDAR-DTM-2M-TR14/LIDAR-DTM-2M-TR14.asc, preceeded of course by the rest of the file path to that directory. Finally, tick <b>No data value</b> and set it to -9999. Press ok and it will start working, which may take a while. It should load into QGIS automatically, having asked you what projection to use (OSGB36 again), but sometimes the process crashed. Don't worry, because the creation of the file has completed, so back on the QGIS main screen, press the Add Raster button and load the newly created file. Having merged all the files, you can delete all the original small unmerged files if you want, since they are pretty big. By default, you get the data displayed as a grey scale image with white as high and dark as low, as shown below.</div>
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<a href="http://4.bp.blogspot.com/-9xQ3RrUh_XU/Vj-0rSljE5I/AAAAAAAAAgE/PXIQPcrjkec/s1600/lidar1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="http://4.bp.blogspot.com/-9xQ3RrUh_XU/Vj-0rSljE5I/AAAAAAAAAgE/PXIQPcrjkec/s400/lidar1.jpg" width="398" /></a></div>
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You will notice that if you have more than one of these next to eachother, the edges don't match, so we need to set them to have a matching palette. We will also use a multi colour palette to provide a bit more contrast. Pick an image, right click it in the project window and select <b>Properties</b>. Go to the <b>Style</b> tab and change the <b>Render type</b> to Singleband pseudocolor. Then use the <b>+</b> sign to add bands. I currently use 0m-Black, 20m-Green, 40m-Brown, 60m-Orange, 80m-yellow and 100m-white. You can of course make up your own palette to suit your tastes. It should look something like this.</div>
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<a href="http://1.bp.blogspot.com/-xuUTzQnLd34/Vj-2LHRKwZI/AAAAAAAAAgQ/vY5zXA8yVlU/s1600/lidar2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="367" src="http://1.bp.blogspot.com/-xuUTzQnLd34/Vj-2LHRKwZI/AAAAAAAAAgQ/vY5zXA8yVlU/s400/lidar2.jpg" width="400" /></a></div>
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You can then right click on your image in the project window and select <b>Styles > Copy Style</b> and then right click on the rest of the images to do <b>Styles > Paste Style</b> to avoid entering that palette information all over again. This should give you something like this.</div>
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<a href="http://3.bp.blogspot.com/-UUVcZP2W1tA/Vj-2w2eMotI/AAAAAAAAAgY/IOyKE1hW_qk/s1600/lidar3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="http://3.bp.blogspot.com/-UUVcZP2W1tA/Vj-2w2eMotI/AAAAAAAAAgY/IOyKE1hW_qk/s400/lidar3.jpg" width="400" /></a></div>
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This shows the height information very well, but if you want to see small changes that might be created by archaeology, then we need to add a hillshade to this. To do this, go to <b>Raster > Analysis > DEM</b>. In the <b>Input file</b>, select one of your merged files. For the output file, use the same filename, except add -HS just before the .asc. You will notice that the resulting file will completely obscure the height data below. To fix this, right click on your newly created hillshade image, go to <b>Properties</b>, go to the <b>Transparenc</b>y tab and move the slider until it is at 50%. You should now be left with something like this. If you zoom in with QGIS, you will see a lot of the smaller features. Happy hunting!</div>
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David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com3tag:blogger.com,1999:blog-5157785897936147656.post-16302818783182281642015-09-29T07:29:00.001+01:002015-09-29T07:29:12.233+01:00Green Waste, A Growing Problem<div style="text-align: justify;">
A relatively new, but increasing, bane for geophysicists and metal detectorists alike, is the practice of spreading green waste on fields. Part of the drive for increased recycling in society, which is good, this material comes from our gardens, but is rarely pure. Many households are not too fussed with what they will put in their bins, so plastic and metal will end up in the green waste. Farmers will buy this from the council and then use it to fertilise their fields. The metal component of this will cause problems for magnetometers, producing white noise from thousands of tiny dipoles. For example, this is a Roman settlement :</div>
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<a href="http://2.bp.blogspot.com/-1aLayBF9-jI/VgouAOAy93I/AAAAAAAAAfM/xf5ftum4SWc/s1600/steynday1proc.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="http://2.bp.blogspot.com/-1aLayBF9-jI/VgouAOAy93I/AAAAAAAAAfM/xf5ftum4SWc/s400/steynday1proc.png" width="400" /></a></div>
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This is a Roman villa :<br />
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Once it's in there, it's there for good. Metal detectorists get it worse, as they are also picking up non-ferrous material. There is even a <a href="http://bangreenwaste.blogspot.co.uk/">blog dedicated to the problem</a>.<br />
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<br />David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com2tag:blogger.com,1999:blog-5157785897936147656.post-54025699883084028442015-09-05T06:55:00.000+01:002015-09-05T06:55:28.788+01:00Latest Results: Chichester<div style="text-align: justify;">
This year, my biggest project was spending a week within the Chichester town walls, looking for Romans with the GPR. The original purpose of the visit was to test the theory that Stane Street did not start at the east gate, but actually went through the Roman town and out the other side. It soon became clear that the archaeology was too shallow to be visible amongst the modern services. Instead, I ended up surveying some grassed areas to look for signs of the Roman town. This is just a quick summary, but you can read the full report <a href="https://www.scribd.com/doc/278592045/Snuffler-1504">here</a>.</div>
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There were two main areas I surveyed. The first was in Priory Park, in the NE corner of the Roman town. The survey revealed two Roman buildings south of the Guildhall and part of the Roman road grid internal to the town to the east, with some low status settlement. The road had been cut in two places by the medieval motte and bailey ditches. You can see a video of the results <a href="https://www.youtube.com/watch?v=1FuS7dFGW6k">here</a> and of the two buildings <a href="https://www.youtube.com/watch?v=oJlrbqcUA-c">here</a> and <a href="https://www.youtube.com/watch?v=sXom0DablT8">here</a>.<br />
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<i>Priory Park Interpretation. Click for larger image.</i></div>
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The second area surveyed was the amphitheatre, just to the south-east of the Roman east gate. It isn't in particularly good condition, most of the retaining walls have been robbed, but some structure is still visible. You can see a video of the results <a href="https://www.youtube.com/watch?v=54RNt7xFT5s">here</a>, but on that version, a block of data is shifted from where it should be.<br />
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<a href="http://1.bp.blogspot.com/-ezyaZu8uvgo/VeHbhocgdwI/AAAAAAAAAeQ/41NxQ2TRFkE/s1600/aminterp.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="350" src="http://1.bp.blogspot.com/-ezyaZu8uvgo/VeHbhocgdwI/AAAAAAAAAeQ/41NxQ2TRFkE/s400/aminterp.jpg" width="400" /></a></div>
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<i>Amphitheatre Interpretation. Click for larger image.</i></div>
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While these are excellent results, they are nothing compared to what is currently being found at Verulamium, where they are using mag and radar to reveal the structure of the town. I'd like to give a shout out to <a href="https://hertsgeosurvey.wordpress.com/">their most excellent blog</a>, which shows the results in great detail. Well worth a read.<br />
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David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-89019152961663475162015-07-12T15:59:00.000+01:002015-07-12T15:59:00.980+01:00Digging Up The Geophysics: 2015<div style="text-align: justify;">
The new archaeology digging season is underway, but is far from over! If you fancy having a dig this summer, here are some sites in Sussex under excavation on which I have previously done geophysics. At the end of the season, I will do another post about what they have discovered.</div>
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Ovingdean</h3>
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<a href="http://www.brightonarch.org.uk/">Brighton and Hove Archaeological Society</a> are again digging at the <a href="http://geophyswithsnuffler.blogspot.co.uk/2014/12/latest-results-ovingdean.html">medieval site at Ovingdean</a>, where are are uncovering part of the enclosure around the manorial enlosure. What they have looks much more substantial than a simple retaining wall. Are there more buildings against the edge of the enclosure?</div>
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Plumpton</h3>
<a href="http://www.sussexarchaeology.org/">The Sussex School of Archaeology</a> are running a training dig at <a href="http://geophyswithsnuffler.blogspot.co.uk/2014/04/latest-results-plumpton.html">Plumpton Roman Villa</a>. The digs run during the week and are targetting the eastern part of the villa.<br />
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Barcombe</h3>
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<a href="http://culverproject.co.uk/">Culver Archaeology Project</a> are digging again at <a href="http://geophyswithsnuffler.blogspot.co.uk/2013/02/latest-results-barcombe.html">Bridge Farm</a>, where they are targetting the intersection ot two Roman roads and the defensive enclosure around the centre of the settlement. When I visited, they were exposing a possible cremation burial and had found an intaglio. Their site has a weekly blog to keep up with what is going on.</div>
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<br />David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com1tag:blogger.com,1999:blog-5157785897936147656.post-73316217289629045682015-06-24T20:22:00.000+01:002015-06-24T20:22:49.456+01:00Version 1.15 of Snuffler released<div style="text-align: justify;">
A small update to Snuffler this time around, though bigger things are already in the pipeline for the future. This time sees the addition of an import for files generated by the new<a href="http://www.rmfrobisher.co.uk/"> Frobisher TAR-3 earth resistance meter</a>. Low cost options such as this are the way that community archaeology groups get started with geophysics, so it is always nice to see new options on that front. I haven't used the new hardware myself, so I can't comment further on it, but I wish them all the best in their new endeavour.</div>
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You can download the new version at the <a href="http://www.sussexarch.org.uk/geophys/snuffler.html">usual place</a>.</div>
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This blog has been fairly quiet as I have been working on some big new projects and finishing work already reported on here, which you will hear about later. In the mean time, here is a picture from the Severn Sisters, where the <a href="http://www.nationaltrust.org.uk/birling-gap-and-seven-sisters/our-work/seven-sisters-archaeology-project/">National Trust are running an archaeological project this year</a>. This is from Bailey's Hill, where some possible Bronze Age remains are due to be excavated in August. If you would like to get involved, you can!</div>
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<br />David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-29959245498944906462015-05-26T19:26:00.000+01:002015-05-26T19:26:53.496+01:00New Toy: Survey Grade GPS<div style="text-align: justify;">
I have a new toy! Oh joy, a new toy! This isn't actually a new piece of geophysics equipment, but survey equipment. Having previously set out grids using a total station and recorded data on an arbitrary grid, I can now get absolute coordinates, set grids out much quicker and with only a single person. I went for net rover rather than rover plus base as I wanted decent coordinates in the field rather than post processed.</div>
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I eventually chose a <a href="https://www.javad.com/jgnss/products/receivers/triumph-ls.html">Javad Triumph-LS</a>. There were several things that attracted me to this particular model. It received all signals from all constellations (so futureproof and accurate), it was cheap (relatively!) and the company had made an effort to deal with interference due to the <a href="http://www.gps.gov/spectrum/lightsquared/">lightsquared debacle</a>, which is good for me, because part of its job will be sitting on top of my radar antenna. The unit even gives you a relative quantification of interference it is receiving. I put it on top of my radar, turned off, and the value was 4. Turned on, it was 22. Rather than having the receiver on top and data collection half way down the pole, both are combined at the top of a mono-pole. It does seem a bit top heavy and difficult to keep steady, but it will correct itself for pole tilt, which is a nice feature. Control is via a number of hardware buttons and a capacitive touch screen like a smartphone, so the whole thing seems very modern. Getting started with the kit, the support on their forums was excellent. On the downside, I found a few things unintuitive, but most of those can be put down to me being a geophysicist rather than a land surveyor. The receiver has not long been released and the manual still needs a bit of work to deal with the likes of me.<br />
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<a href="http://4.bp.blogspot.com/-zogOUOX-qVY/VWS5id7ULJI/AAAAAAAAAbE/6nyQ3kCS-JU/s1600/IMG_20150526_190554.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="640" src="http://4.bp.blogspot.com/-zogOUOX-qVY/VWS5id7ULJI/AAAAAAAAAbE/6nyQ3kCS-JU/s640/IMG_20150526_190554.jpg" width="475" /></a></div>
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So that's the hardware, which I'm very pleased with. I also needed a network RTK corrections subscription. In the UK, all of the correction services are based off of the base stations run by <a href="http://www.ordnancesurvey.co.uk/business-and-government/products/os-net/index.html">OSNet</a> from the Ordnance Survey. Of the five different services that use OSNet hardware, two are aimed at farming. While these are cheaper, they only connect you to the single base station, which is fine if you are near one, but not very good if you are not. You can only expect to get 5cm accuracy with these services. The other three services, <a class="ga-outbound" data-location="Main content" href="http://uk.smartnet-eu.com/">SmartNet</a> from Leica GeoSystems, <a class="ga-outbound" data-location="Main content" href="http://www.trimble.com/positioning-services/vrs-now.aspx">VRS Now</a> from Trimble and <a class="ga-outbound" data-location="Main content" href="http://www.topnetlive.com/">TopNET live</a> from Topcon do things differently. They create a model of the atmosphere based on a number of base stations and create a Virtual Reference Station based on your current location, giving you a potential accuracy of 1cm. Apparently all three services produce a similar level of accuracy, but they don't give any information on which constellations/signals are corrected or whether they provide any additional base stations over and above those provided by OSNet. Price wise, at the time of beginning to look at all this, their websites showed the Leica and Topcon services charged £1200 ex vat per anum for the limited (40 hour per month) service, while Trimble charged £1500 or £1300 sans SIM card.</div>
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Trying to sign up to one of these services turned out to be a tale of woe. I started out contacting Leica. The contact email address and price on the website was wrong (now fixed) and the price is now £1260. After speaking to someone by phone and then emailing, contact went dead and they stopped replying to my emails. Not very good if they don't even want to sell you something. I next tried Topcon. I filled in their web form and got an email saying that my registration was confirmed... then heard nothing for a week. Next I tried Trimble. I filled in their web form, which then demanded that I give them my VAT number. Not even having a company, I don't have one of those, so Trimble fell at the first hurdle. They were too expensive anyway. I went back to Topcon, having noticed another contact email in their confirmation email. Once I had the attention of a human, service was prompt and helpful. There were further problems, like the first SIM card they sent got lost in the post and the second one was the wrong size (mini instead of micro), so I <a href="http://www.cnet.com/uk/how-to/how-to-cut-your-own-micro-sim-card/">cut that down to size</a>, but I messed it up and cut it slightly wrong. They sent me a SIM of the correct size and all was well in the end, so Topcon came out on top(con). Connecting to the service, I got my desired 1cm accuracy. According to the receiver, it was receiving correction for GPS + GLONASS. Hopefully, the Ordnance Survey will upgrade their base stations to cover Galileo now that constellation is coming online.</div>
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One thing I wanted to test is that the receiver supported the black abomination that is <a href="http://www.ordnancesurvey.co.uk/business-and-government/help-and-support/navigation-technology/os-net/formats-for-developers.html">OSTN02</a>, a modification of <a href="http://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid">OSGB36</a>. I surveyed a random point in <a href="http://en.wikipedia.org/wiki/European_Terrestrial_Reference_System_1989">ETRS89</a>, converted it internally to OSGB36 and did the same conversion with the Ordnance Survey's own <a href="http://www.ordnancesurvey.co.uk/gps/transformation">coordinate transformation tool</a>. Initially, it seemed it didn't, as the difference was about 2.06m. It turned out that I also had to change the datum used by OSGB36 to the <a href="http://en.wikipedia.org/wiki/Ordnance_datum">Newlyn datum</a>, which made it produce the same values as the OS site, so all good there. I also wanted to test how accurate Google Earth imagery was locally, so I recorded a bunch of points in ETRS89, converted them to <a href="http://en.wikipedia.org/wiki/World_Geodetic_System">WGS84</a>, as used by Google Earth and converted it to <a href="http://en.wikipedia.org/wiki/Keyhole_Markup_Language">kml</a>. Here is a picture of how that turned out. Looks like the Google Earth imagery is very good indeed!</div>
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<a href="http://3.bp.blogspot.com/-OxeClGWHVUI/VV406eNW6MI/AAAAAAAAAak/H15L3ZFKmDY/s1600/test.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="341" src="http://3.bp.blogspot.com/-OxeClGWHVUI/VV406eNW6MI/AAAAAAAAAak/H15L3ZFKmDY/s400/test.jpg" width="400" /></a></div>
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How do I use this fantastic new toy in the field? With the total station, I used to set up the total station at one end of a baseline along a straight edge of a field, tell it that it was at 500E,500N, point it along the baseline, then tell it that it was facing something like an angle of 270 (west), even though it wasn't. Then I could just go and look for 460E,500N etc. For reestablishing the grid, I used to record two resection points that could be described to a few cm, the downside being that those points could disappear, which did happen in a couple of cases. For placing on maps, I recorded a bunch of points at the edge of the field to match to the edge of the field on maps or aerials. The process is described in more detail <a href="http://geophyswithsnuffler.blogspot.co.uk/2011/09/overlaying-geophysics-results-on-google.html">here</a>.</div>
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With the GPS, I start by collecting the same point I originally would have occupied with the base station, then setting it to stake out to that point and walking 120m away along the baseline. I then do a Multiple Point Localization on those two point, using coordinates of 500E/500N and 380E,500N, which will create a new projection which I can use to walk to further points just as with the total station, only with a single person instead of two. The two points used for the localization are recorded in lieu of resection points, but the new projection is stored on the device, so they are only needed if other people are re-establishing the grid. Since I get absolute coordinates, there is no need to record points around the edge of the field to overlay the geophysics correctly, so everything becomes much faster and more reliable.</div>
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Now to get out and use it. I'm going to be doing a big radar survey of Chichester in July, so watch this space for some results from that.</div>
David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-42816789528519838172014-12-26T22:32:00.001+00:002014-12-26T22:32:47.917+00:00Version 1.14 of Snuffler released<div style="text-align: justify;">
My last post of the year will be for an update to my geophysics software, Snuffler. The new feature this update is an extension of the support for RM15/MPX15/RM85 multiplexing. As well as doing parallel readings, this update will now cope with readings on multiple levels. It is a bit of a nasty hack as far as the user interface is concerned, but it works. Here's how :</div>
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Normally, you download your data into an import file, then export from that into grids. Job done. With multiple levels of multiplexor data, there is an extra stage in the middle. In the initial download, you select the total number of readings recorded each time you put the probes in the ground. For example, if you record two readings with 0.5m probe spacing and one reading at 1m probe spacing, that would be a total of three readings at each point.</div>
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When you export from this import file, rather than getting grids, you will be asked which readings you will be exporting at this level, creating a new import file containg just the readings at that level, from which you export grids in the normal way. In the above example, you would create two new import files from the original import file. The first file would contain readings one and two and the second file would contain reading three. Full details on how to do it properly are listed at the bottom of the Import Files section of the help file.</div>
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I didn't have access to a machine when developing this, so it may not work perfectly. If you try this yourself and do have problems and the help file is not being helpful, please let me know. Many thanks to two of my users, Helen and Manuel, for helping me test this.</div>
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You can download the new version at the <a href="http://www.sussexarch.org.uk/geophys/snuffler.html">usual place</a>.</div>
David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-65937941921110271622014-12-08T21:00:00.005+00:002014-12-08T21:00:59.806+00:00Latest Results: Ovingdean<div style="text-align: justify;">
<a href="http://www.brightonarch.org.uk/">Brighton and Hove Archaeological Society</a> are a very active group fieldwork wise, with an insanely long digging season and a lovely supportive approach to new diggers. It was with BHAS that I started doing geophysics, with Bill Santer teaching me how to do earth resistance. Bill sadly passed away this year, so I would like to dedicate this survey to him, the fantastic bloke who started me on this path. He will be sorely missed.</div>
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The site that BHAS have been digging this year is at Ovingdean, where there is a medieval manor complex within an earthwork enclosure next to the church. They have done a few seasons of excavations here on one side of the enclosure, based on some earth resitance they did before I started doing archaeology. They have excavated the main manor house, which has very chunky walls and an undercroft, and this year they have been excavating what looks like a post built barn structure next to it. There is still the other half of the enclosure unexcavated, and BHAS wanted to know what was there.</div>
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First, the original earth resistance, flattened with a high pass filter so you can see the main manor building amongst the rubble near the churchyard wall to the south-east. A trackway snakes through the middle of the enclosure from an entrance in the south-east and possibly out the other side to the north-east. To the north-west, parts of the enclosure revetments and bits of masonry buildings up against the earthwork enclosure can be seen.</div>
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<a href="http://2.bp.blogspot.com/-w-X6Omz9ziQ/VIYMG5cRuTI/AAAAAAAAAXo/_Nyv2f94epc/s1600/resflat.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://2.bp.blogspot.com/-w-X6Omz9ziQ/VIYMG5cRuTI/AAAAAAAAAXo/_Nyv2f94epc/s1600/resflat.jpg" height="362" width="400" /></a></div>
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<i>Earth Resistance. Click for a larger image.</i></div>
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This year's surveys include magnetometry and GPR. Being chalk, the magnetometry results are predictably rubbish, but do show hits of the enclosure to the south-west. Much of the north-west part of this survey is obscured by the magnetic halo of a large water unfortunately.</div>
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<a href="http://1.bp.blogspot.com/-ARj1U7RSWkg/VIYNQdE7oYI/AAAAAAAAAX0/wLcBd33yz6w/s1600/mag.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://1.bp.blogspot.com/-ARj1U7RSWkg/VIYNQdE7oYI/AAAAAAAAAX0/wLcBd33yz6w/s1600/mag.jpg" height="362" width="400" /></a></div>
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<i>Magnetometry. Click for a larger image.</i></div>
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The GPR was a lot more productive, showing what looks like an open sided barn and an attached dovecote against the north-west enclosure earthwork. Signs of the outer enclosure revetment are visible in other layers further down.</div>
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<a href="http://2.bp.blogspot.com/-suC6pUXHsAw/VIYPIszS8nI/AAAAAAAAAYA/DMm7_2C40jY/s1600/gpr2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://2.bp.blogspot.com/-suC6pUXHsAw/VIYPIszS8nI/AAAAAAAAAYA/DMm7_2C40jY/s1600/gpr2.jpg" height="362" width="400" /></a></div>
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<i>A single GPR slice. Click for a larger image.</i></div>
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If you want to know more, you can <a href="https://www.scribd.com/doc/249561589/Snuffler-1404">read the full report</a> or <a href="https://www.youtube.com/watch?v=m5fUsP_entc">watch a video of the ground penetrating radar</a>.</div>
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David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0tag:blogger.com,1999:blog-5157785897936147656.post-69252235434928903672014-12-05T07:40:00.000+00:002014-12-05T07:40:02.290+00:00NSGG Conference 2014<div style="text-align: justify;">
The time came once again to attend the <a href="http://www.nsgg.org.uk/">Near Surface Geophysics Group</a> <a href="http://www.nsgg.org.uk/meetings/nsgg2014/NSGG_programme_2014_v2.pdf">conference</a>, which is held every two years, the last being in <a href="http://geophyswithsnuffler.blogspot.co.uk/2012/12/nsgg-conference-2012.html">2012</a>. As always, the chats in between lectures were the best bit. My ego was thoroughly strokes by three people coming up to me out of the blue and complimenting me on Snuffler. It's a wonder I got my head out of the door at the end of the day. I also spoke at length to <a href="http://www.utsielectronics.co.uk/">Erica Utsi</a> to enquire about attaching my forthcoming purchase of survey grade GNSS to my GPR.</div>
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The talks were many and varied. There were 12 of them! My favourites were :</div>
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Kris Lockyear talked about getting community archaeology groups involved in geophysics and some of the results they had. The survey of part of Verulamium. A grant bought a fancy mag cart, which seem to be everywhere these days, which the various groups share, with training days on how to use it. This sort of work is excellent for getting smaller groups who otherwise would not have access to geophysics. They have an excellent <a href="https://hertsgeosurvey.wordpress.com/">blog</a>.</div>
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The talk I was most looking forward to was Armin Schmidt (of course) talking about inversion modelling for magnetometry. It seems the subject is a lot more subjective than I imagined, with various models of 3D interpretation potentially fitting the 2D data. I asked where I could find out more about how this was done, as I was thinking of incorporating this into Snuffler. The ripple of laughter that went around the room suggests that this is a black art best left to the damned.</div>
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Pope-Carter (I think) spoke about some open source software for geophysics being developed in python by students at Bradford called <a href="http://www.archaeopy.org/">ArchaeoPY</a>. It was explained that a lot of the work of writing display stuff was already done and available in easy to use python libraries. A lot of the functions already available in the software were shown. The whole thing is impressive and has a lot of potential. Being open source, if there is a feature you think is missing, you can go ahead and add it yourself!</div>
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There were two interesting talks from overseas. Someone from Italy talked about the sites found there, including GPR over a proper Roman road with kerbstones and all, which was very nice to see. I do like a bit of Roman. Someone from Canada produced some actually really good plots using EM of buildings, probably because the remains were shallow. Perhaps EM isn't so bad after all, or maybe you just have to do it at the insane resolution that they did. Both speakers lamented the lack of understanding of geophysics there by the relevant cultural authorities.<br />
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More Roman from the <a href="http://www.arch.cam.ac.uk/research/projects/canterbury-hinterland">Canterbury Hinterland Project</a>, both close to me and Roman, my favourite. It is run by institutions outside of Kent, since no-one in Kent seems to do geophysics. Some of the buildings they found using high res radar were quite impressive, and odd looking. There was also an interesting attempt to clean up the rather messy GPR data, using a different method than Armin suggested two years ago. I think this was my favourite talk of the day.<br />
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Then, of course, there was the usual posters, many more this time around. The judging was by popular vote rather than the usual panel, so I'm wondering if it will end up a bit like the Eurovision Song Contest with everyone voting for their mates. I certainly did :)<br />
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Hardware wise, mag seems to be heading for multi-sensor carts, some of which were evident in the talks, posters and commercial exhibitors. The greater speed and resolution can only be a good thing. I just don't understand how people afford these things.<br />
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All in all, another good year.<br />
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David Staveleyhttp://www.blogger.com/profile/11829147049242240411noreply@blogger.com0