18th September 2013, 06:34 PM
Dinosaur Wrote:Geophysics is only really any good for spotting cut features, walls, burnt things and, occasionally, stuff like surfaces, when it works at all. That's where other types of evaluation like fieldwalking come in - flint scatters are usually entirely in the topsoil and don't show on any type of geophysics, for instance, but of course usually go away when you topsoil strip, will shortly be having that one out with a client...
There are other useful applications for geophysical survey, for example electrical sectioning/electromagnetic survey techniques can be very helpful in modelling the extent and 3d subsurface architecture of archaeological and palaeo-environmental sequences. Very useful on alluvial sites with deeply buried former channels and land-surfaces - the type of places where traditional evaluation trenching can be arduous and expensive. Combined with some boreholes and test-pits/trenches for near surface remains such survey can help you very quickly build up a decent chrono-strategraphic sequence that you could never achieve with trial trenching alone.
There are certainly some situations where lots of survey methods combined can be much more powerful than the sum of their parts.
What I don't like is when a negative geophysical survey in isolation is used as a reason for not doing further archaeological works. All the survey can show is what it has found - what it won't show is what it hasn't/couldn't find. There can be all sorts of reasons why geophysical survey fails - be it the type of geology, nature of archaeology, nature of overburden, past land-use, etc, etc.
That doesn't mean its not useful - indeed sometimes its invaluable - for example rapid survey along a broad pipeline corridor can be helpful to inform initial routing decisions (yep along with other techniques maybe fieldwalking, walkover, predictive modelling (!) - you'd never be able to evaluate such wide swathes of countryside at the options stage by trial trench (sorry unit). Once the line's been fixed you can move on to intrusive techniques, but these often provide little more than a long transect through the landscape - bits of sites captured within the easement. The geophysical survey will have covered a much wider area allowing you to start seeing your site in its wider context.