Beyond the eye of the beholder

[John Wells]

I was rather hoping that someone may have just popped a UV-pass or near IR filter on their camera and taken pictures in trenches, or over small areas, with the aid of a tripod (because of the long exposures involved) using their normal camera. My impression is that near IR is less useful on exposed soil but near UV may have some potential, especially for fine detail. We will be looking at this more carefully in the near future. I am just waiting for a UV filter for the cheap 808#16D camera, to see if we can improve on exposure times with its standard lens. A conventional UV camera is too expensive and may not be worth the expense, especially in a community context. However, the smaller micro cameras can be fitted with much cheaper UV lenses which are normally used in machine vision applications.

Generally, in the near infra-red, with crop marks and latent crop marks and parch marks, bright sunlight can obscure them, but not always. In sunlight, there is often little difference between the near IR and the red channel taken from the visible spectrum.
Near IR seems to be at its best on short grass in overcast conditions, but this may reflect our limited experience.

Beyond the near-IR, with thermal imaging, everything is about timing and, with thermal crop marks, you even have to consider relative humidity. We have done little thermal work, so far, but with the conditions here in Scotland, we believe that we are more likely to see thermal crop marks than conventional ones....the problem is the timing!
Differential warming and cooling of ground features is less problematic:

Near IR
l Thermal vertical Thermal