Beyond the eye of the beholder

[John Wells]

Are there any readers of this forum who have looked at an excavated site just beyond both ends of the visible spectrum (near IR/UV), using any technique, but especially ground-based?

[Hamish]

I'd upload a picture if I could (Uploading or inserting photos from other locations ends in errors). But it is probably not what you are looking for John. Here is a link:

http://testarea.hdf.me.uk/IMG_2107bXX-rh-bajrfed2.jpg

The photo on left is normal colour, the right is near-infrared - 760nm filter.

The big curving feature is a ditch belonging to a banjo enclosure.

[Oxbeast]

Very interesting Hamish, I've seen this working with cropmarks where some elements of a site can show up earlier because of the way the vegetations responds. However, I can't see much differerence in what is showing up between your two photos. Did more stuff show up and I am just not seeing it?

[Hamish]

I cannot see much difference either. On cropmark sites Where I have flown a near-infrared camera, in most instances the infrared has not shown up any more information than has been obtainable from the colour spectrum - I have only one example at the moment where infrared on cropmarks was significantly better than colour.

[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

[kevin wooldridge]

I await the results of your experiment with interest John. As you say the thermal technique could work in Scottish climate conditions and I would be interested in its potential application to summertime Norway....a small paper in the BAJR technical series outlining the techniques and equipment required would be appreciated if you have time and patience....

[John Wells]

Some basic information is here: http://www.armadale.org.uk/phototech.htm but it is beginning to look a little dated.
I will be putting something here: http://www.archaeolandscapes.eu/index.ph...v/417.html but that might be more about flying kites with cameras initially.