05 September 2011

Earth Resistance Replacement?

I've been pondering the nature of earth resistance in archaeology, mostly because it is so darn slow. There has to be a quicker way of getting this sort of data. I'm sure you all know the standard way of doing things, with a twin-probe array. You also know that the main thing it reacts to is a change in the moisture in the ground. There are other ways that you can measure ground moisture, however, without sticking metal probes in it. I must admit that I know little about these methods, and hence I am looking for comments on their possible effectiveness.

Electrical Conductivity

Conductivity is already established as an archaeological tool, albeit a little used one (at least in the UK). It works by inducing a magnetic field, similar in a way to a metal detector, though not quite. As you can see (with the Geonics instruments), it has a similar collection method to magnetometers, which is good. Unfortunately, the effectiveness compared to traditional resistivity has been questioned, with the results apparently being a lot less clear.

Thermal Imaging

As everyone knows, water is very good at holding heat, but can this be exploited for archaeological purposes? Thermal imaging cameras are commercially available, for example, from FLIR. They can be cheap to astoundingly expensive, depending on the sensitivity and resolution of the instrument. The question is, does any temperature difference under the surface have a measurable effect on the surface, where the camera is looking? If so, it would mean a very quick means of collection, perhaps with the aid of a small tethered balloon to dangle the camera from, or a UAV, assuming it can carry the weight. Most likely though, it wont be as effective in getting the depth needed.

Microwave Radiometry

Jumping past the other end of the visible spectrum, there is another means of measuring ground moisture, with a microwave radiometer. I was first alerted to the possibilities by this article. Their general use is for meteorology, and deployed in satellites, but you can buy smaller versions. Is it possible to point one of these at the ground and measure the moisture? What would be the depth penetration? How would it be affected by plants? Again it may suffer from the same limitations as thermal imaging.

If anyone knows more about these the science involved, then please post a comment. It's all hardware to me, and I'm a software guy.

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