I managed to get to the Near Surface Geophysics Group Conference this year. It was good to chat to a few old faces, such as swapping geophysics software notes with the author of Archaeosurveyor, a thoroughly nice chap. I also spoke to Erica Utsi about buying a GPR, but I have yet to hear from anyone who has used one yet. I was quite impressed by what I heard, but I haven't got the money to buy one quite yet. Sometime next year hopefully. So what about the talks. Many of them used the sort of equipment that you can buy when money is no object, as it seems to be for academic departments, but it is not all about the bling. It's not even about the pretty pictures, though that helps. It's about some of the new ideas and how people go about things differently. Here are some of the highlights for me.
James Bonsall talked about a new EM instrument called the CMD Mini-Explorer. I hadn't been hugely impressed by the results from EM in the past, but the results shown in the talk were quite impressive. The instrument takes both In-Phase and Quadrature readings at three different depths, increasing the chance that you will find something. The speaker said it gave better results and was easier to use than the Geonics EM38, though someone from Geonics in the audience suggested that a lot of the problems that the speaker had described had been sorted in the EM38 MK2, which takes readings at 2 depths compared to the 3 of the CMD. It would be interesting to hear from someone who has used both of these.
Armin Schmidt talked about GPR. This time, he took data from a Roman era cemetery and converted the raster data to vector data. This allowed him to use various GIS functions to process that data into a more agreeable format for viewing in 3D. You don't get the fine detail, but it makes things much easier to see for the average person not used to staring at geophysics plots.
James Lyall, famous in geophysics circles for the giant survey in the Vale of Pickering, talked about a national archive for geophysics results, much in the same way as aerial photography achieved. It is actually quite hard to get your hands on the data for any given geophysics project, and it is rare for any geophysics practitioner to store the data in any readable form outside the survey report. It is certainly possible, but it takes time and is expensive, so most surveyors don't. James asked the audience to get their collective heads around the problem.
Robert Fry talked about the work of the DART Project, which is something I've had my eye on for a while. One of the things they are attempting to do is see how earth resistance changes over the course of a year. Robert explained how they found a ditch feature using magnetometry, then put a series of fixed resistance probes across it in order to find out how the contrast between the ditch and its surroundings changed over time. Not surprisingly, the very wet weather in 2012 made everything waterlogged and made the ditch all but invisible to earth resistance for most of the year.
James Bonsall (again) talked about ground truthing geophysics data by comparing geophysics survey results to excavation results in Ireland. Most of the work was done with magnetometry, and the results showed a big difference depending on which geology the survey was taken, with limestones suffering. The results were broken down into true-positives, where both geophysics and excavation found features, true-negatives where neither did, false-positives where the geophysics found something but the excavators didn't, and
false-negatives, where the excavators found something that the geophysics hadn't spotted. The speaker suggested that for certain geologies, alternative methods to magnetometry, such as EM, should be used. Some members of the audience didn't agree with this, and suggested that, in particular, there wasn't a problem with limestones in mainland UK. Some also suggested that many of the false-positives were down to the excavators machining through shallow features, which everyone seemed to agree with.
Just for the pretty pictures this one. Lieven Verdonck demonstrated the sort of results you could get when you perform a GPR survey on a Roman town in Portugal at an absurdly high resolution. Nice if you have the time for it, and the results were certainly worth it, with very clear high resolution wall lines.
Closer to home, Paul Cheetham has been doing a very similar thing in Dorset as I have been doing in Sussex, and examining Roman rural settlement on a grand scale. The sort of results he was getting was quite familiar to me, and made me feel right at home amongst all the speakers with their expensive bling machines.
