Latest Results: Plumpton

Late last year, I was involved with a magnetometer survey of Plumpton Roman villa with Chris Butler Archaeology Services on behalf of Plumpton Agricultural College. This means that his team did all the hard work and I processed the data. As the villa foundations were constructed of flint, it doesn't show up, but the enclosure around it does. There are also strong magnetic readings at either end of the enclosure, which may relate to a hypocaust system. There were also signs of field systems associated with the villa to the south, and a possible Roman road to the west, which I was very pleased about. This pattern of a road passing rather than heading to a villa is repeated elsewhere, such as Barcombe.

Plumpton Villa magnetometry

At the time time, David Millum of the Culver Archaeology Project led a team surveying the villa itself with an earth resistance meter, which showed up the walls very nicely. It seems to be a standard winged villa, but with the western wing extending further to the north and west than it should. The villa as a whole looks like it has at least two phases. At either end, where we get the strong magnetic responses on the magnetometry, we also get strong high resistance areas, showing more than just the walls. Maybe it is just rubble, maybe it is something to do with a hypocaust.

Plumpton Villa earth resistance

This weekend, I taught a geophysics dayschool here as part of the Sussex School of Archaeology. As well as covering the usual earth resistance and magnetometry, we also did some resistance tomography and a single line of radar, both along the green line in the images below. I have layed them out horizontally at the correct position next to the green line that they were surveyed along, so just imagine that they are vertical slices through the ground along that line.

First the tomography. Several of the walls show as red points towards the top, plus at either end of the villa, we get broader and deeper high resistance confirming the standard earth resistance. There is also a hint of something heading further down under the ground at either end.

Plumpton Villa resistance tomography

Finally, the single line of radar we did. The ground was a bit wet, so the top layer is a bit of a mess, but many of the walls are still visible below that. The two walls visible in the centre of the villa are at the expected depth, but those to the west and east are deeper, further suggesting a hypocaust system.

Plumpton Villa GPR traverse

The Sussex School of Archaeology will be running a training excavation on the villa in the summer of 2014.

Version 1.13 of Snuffler released

It's time for a new version of Snuffler, and this version is all about importing stuff. There are two new files imports for getting data into Snuffler.

The first is for importing TerraSurveyor (was ArchaeoSurveyor) grids and composites. TerraSurveyor is a (very good) commercial equivalent to Snuffler. Someone sent me some data in that format, so I took the opportunity to write an import for it.

The second is Surfer ASCII grid files, not to be confused with the ASCII Grid files that ESRI produces. Surfer is software for displaying 3D geographical data. It wasn't data from that software specifically that I was trying to import though. ReflexW, the GPR software I use, has an export function for time-slices in Surfer ASCII grid format and I wanted to play around with slice data in Snuffler. Here is a time slice from the site I covered in my last post display in Snuffler.

You can download the new version at the usual place.

Geophysics on WWI Camp in Eastbourne

World War I is very much in the news at the moment, due to the centenary, so here is some WWI geophysics to entertain you. The site is the extreme south-east corner of Summerdown Convalescent Camp in Eastbourne, which is very near where I live. I got to use my new GPR system, which is always good, and it showed up the archaeology quite nicely. In the area surveyed, there are ablution and barrack blocks. The former have fairly solid foundation structures while the latter were built on a series of concrete piles. See if you can spot the in the image below. I would compare this to what was excavated... but no-one told me when the excavation happened. You can see the full report here and watch a movie of the time-slices here.

News and more talking

Hello everyone. It's not a time for geophysics, being winter, so it is writing and talking time. For those of you who wondered where my website for Snuffler disappeared to, the company that did my web hosting fell off the edge of the world, so I had to spend some time regaining control of my domain name and sorting out new web hosting. All is well now.

I've mostly been spending my time writing a chapter on Roman roads for a book entitled Archaeology and Land-use of South-East England to 1066, which is being published as a tribute to Peter Drewett, who died last year. Having only knowledge of the Sussex area, I have been furiously researching what has been going on in Kent and Surrey since Margary's day. Thanks to a number of people from those counties, my task has been made somewhat easier. The book should hopefully appear in 2015.

My first talk of the year will be at the Lewes Archaeological Group, where I will be talking about Roman roads in the Lewes area, where I seem to be doing a lot of my geophysics surveys. The talk is at Lewes town hall on the 31st of January 2014 at 7:30pm.

Readers of my blog will remember me talking about Oaklands Park in Sedlescombe here and here. Well now the final report is online. If you don't fancy reading a long geophysics report, you can hear me talk about it on the 17th of February 2014 at 7:30pm. The venue is Pestalozzi, on whose land the majority of the work was done.

Finally, I will be running a series of dayschools at the Sussex School of Archaeology. It is a two day course. The first day will be out in the field, learning about earth resistance, resistance tomography, magnetometry and ground penetrating radar while the second day will be indoors, covering theory, data processing, interpretation and the effects of geology on geophysics. As there will be limited space on the first day, I have split that into two groups on the 5th and 12th of April 2014, with the two groups coming together for the day in the classroom on the 13th of April 2014.

Then, I will be all talked out and will return to the field for more geophysics.

Version 1.12 of Snuffler Released

Another small update for Snuffler today, which will hopefully make the destripe filter easier to use.

A feature of the destripe filter that is useful, but many don't understand is that when reading through each line of data, it will restrict any readings it comes across that are outside the display bounds to the level of the display bounds, so if there is a reading of +60nT and the display bounds are +/- 2nT, that reading will be treated as +2nT. The benefit of this is that particularly strong features will not affect the filter too much, which would stop stripes being left visible even after filtering. The downside is that if your striping is particularly severe, you would need multiple passes of the destripe filter to get rid of the stripes, as it would only remove a maximum of 2nT (the display boundary) each time. This downside became most obvious a few versions back when I changed the default display boundary for mag data to +/-2nT rather than calculating a range from the readings in the file, which is more suitable for resistance data. The fact that you needed to do multiple destripes was not obvious to all of my users, and to be honest, it shouldn't need to be run multiple times, so I created a new destripe type, which is now the default, which will do multiple passes of the filter, so you don't have to. You still have the option to do a single pass if so desired.

The other noticeable change is that help file should hopefully work for more people now. I had several complaints that it wasn't, but couldn't replicate the problem on my machine. Having found a machine where it doesn't work, there should now be a workaround which will make it work for some people at least. If it still does not, let me know.

Changing the subject, if you fancy seeing me talk about geophysics and Roman roads, I will be at the CBA SE conference in Faversham on the 16th of November.

Latest Results: Barcombe (and Roman agricultural planning)

Now the crop is coming of at Barcombe, I have returned for some more magnetometer survey at Bridge Farm, extending the settlement eastwards. The process was speeded up with the aid of a second Bartington, which was on loan to the Culver Project from AOC Archaeology following the recent excavations. Members of the Culver Project and Ringmer Group aided with the survey, enabling the area to be finished in a day. Here are the results.

Latest results. Click for a larger image.

The roadside settlement continued east, with strong evidence of settlement close to the road. The extent of the settlement either side of the road is less than to the west, but it is still substantial. The strong pit features cluster within 50 metres of the road, with a very strong outlier to the north-west, which may be some sort of kiln. One puzzling element are the two linear features heading north and south, at a different alignment to the road. They are parallel to eachother, but their alignment is strange. Eventually, I worked out that they are exactly parallel to the Barcombe to London Roman road, which is further to the west, as seen in the image below.

Click for larger image.

What I had been expecting is more of the carefully laid out ditches near the centre left of the image, where a square block of land had been marked out with side of 4 actus. An actus is a unit of Roman measurement used for setting out land in an ordered way, set up by Roman surveyors in a repeating pattern of squares known as a Centuriate. I was hoping to see this continue to the east, but my theory was wrong. Instead we found these linear features extending out at the same angle as a Roman road about 300m to the west. Was there some link between the two?

Click for larger image.

Rather fortuitously, a further example of exactly this had been found recently by members of the Culver project using their borrowed magnetometer. They had been looking at more of the north-south Roman road that the project had found to the west of the river. These fields have been more heavily ploughed, so the results are not as clear. As well as the road, they have found a series of ditches parallel to the road. One of the measurements in between ditches is 2 actus, but the further ditch is 5 metres above the 2 actus mark.

Is this an example of Roman planned cultivation? The results in the image above seem sparse. Either the more shallow ditches have been ploughed away, or only part of the system was surveyed and never used. Hopefully this is something further geophysics will answer.

Latest Results: Oaklands Park

I did buy the Groundvue 3A ground penetrating radar cart that I discussed in my earlier post, and have been giving it a go at Oaklands Park, where I did a large magnetometer survey with IHRG a while back. There were a few areas where we thought that there might be a possibility of buildings. The results have been very positive. The two survey areas we covered, outlined in red in the image below, are 40x40m and overlap as we found that the building was on the edge of the first grid we did. The first area, to the north-east, was recorded down to 70ns. The second area, to the south-west, was recorded down to 50ns.

GPR survey areas. Click to enlarge.

There are interesting features at various levels, and to get a full idea of them all, you need to look at different depths. Below are features from 10ns and 13ns followed by an interpretation. To get a better picture of what is going on, you can look at the whole lot on youtube. The video for the first survey is here and for the second survey is here.

Features at 10ns. Click to enlarge.

Features at 13ns. Click to enlarge.

Interpretation over magnetometry. Click to enlarge.

You can see in the above image the location of features on the GPR surveys overlaid on the magnetometry results. The most important feature is the building in dark blue. This shows up fully on the magnetometry, but the west wall and a second north wall are missing on the GPR results. This may be due to robbing. The green feature seem to be metalling on a trackway, most likely iron slag. It doesn't extend all of the way along the track, but seems to have been placed outside of the building, which may indicate that this section of the track was busy and in need of repair. The two light blue features are very strong both magnetically and very dense on the GPR results. They may be where the iron was processed. The yellow lines are boundary features, which mark out an enclosure around the building and a further enclosure to the north-east, the other side of the track. The orange areas are large pits. On the GPR results, these can be seen to reduce in size as they go deeper. Light purple areas seem to be dumps of material with no pit. Finally, the small dark purple feature to the north-east seems to be a well. It is circular, with a small L shaped feature attached at higher levels, which disappears further down. While all other features disappear by 30ns, the well keeps going all the way down to the 70ns recording limit.

These GPR results are great. I'm looking forward to using it on a lot more sites in the future.