Photography in archaeology

[barkingdigger]

Kevin, what an interesting thesis - thanks for providing a link! I too would like to see how we integrate the "wrinkly cornflakes" of photogrammetry & laser scanning back into the main strat record - I haven't seen this capability in GIS-based systems. Perhaps a CAD-based dataset, using the GIS functions of Civil 3D (or Kubit's MonuMap?) might get us there? The real issue however is that the image-based models still require interpretation and comparison with the real thing, so to be of use in most field situations you really want to be processing it on site in real time. And what are we wanting as output? Archaeology tends to dwell on edges rather than surfaces because the edges tell us about form (& thus function) as well as hierarchy of creation. If we use photogrammetry just to get outlines, is it truly cost-effective?

By the way, I was surprised to see no mention of Paul Bryan's 2005-6 rock-art project, or the EH tunnelling at Silbury, where Topcon's PI-3000 software was used to create models from stereo pairs of images. (Important mainly because it was an early entry into the "sub-?5k, runs on a laptop" software market...)

[kevin wooldridge]

I agree that Erik doesn't describe every possible use of the method and it is slightly Scandocentric in its parameters. I think he does however cover the cost-anaylsis (somewhere) and compares it to the cost of achieving the same level of data collection using conventional survey means. I agree though that it requires a big powerful computer to deal with the point cloud and that may be sometimes difficult to achieve in a field situation working against the clock - so it is more suited to a quiet day or two in the office.

As for the integration into the strat record, it could be partially achieved by using a true 3-D programme - some variants of GRASS for example (though the chronological dimension may be more problematic), but I don't think that PhotoScan (which is 2.5-D at the best) is the way to that particular end....

[Jack]

Nah, differential melting of snow in a field is usually to do with earthworks, dips and shadows

Here are example of images produced with both snow cover and melt:
http://www.armadale.org.uk/gormyre.htm

Cool. Are those earthworks shown by shadows? Or is there some IR, UV, Thermal giggery pokery?

[Jack]

Are the thermal/hydrological properties of natural and fill different enough to be detectable on anything other than an aerial/satalite image?

Under investigation: http://www.armadale.org.uk/dart.htm
With all the photographic techniques you are looking for any variations, including moisture content, reflectivity, emissivity and thermal inertia etc. In practice, it does not matter initially what the process is, all you want is variation.

Looked at the photos. Am I understanding correct that the strimmed area is over an experimental ditch recently dug and filled in. Is that the light stripe that shows up on the near IR image and less well on the thermal image?

[Jack]

Maybe its something for the future when resolution improves and experiments have ironed out issues.

Resolution is not a problem in photography, even when working with a 320x240 pixel thermal imager on a kite:

(That's me at the centre!)
It is better than the usual 1 pixel equivalent per square metre of geophysical surveys.

An image which inspired me was this aerial one taken with a pencam......Yes! a 352 x 288 pixel pencam:
http://www.armadale.org.uk/cairnpapple050.htm

Not sure what I'm seeing in this image (other than you in the middle). Is there a non-thermal image for comparison? Whats the dark bits (other than cold), whats the lighter rectangular bit on the left, some walls?

[Jack]

err, as I think I've already pointed out, try actually READING my original post and maybe you'll realise how stupid that post is in this context, I specifically exempted earthworks ! !

- on stripped archaeology snow seems to last longer on better draining stuff like gravel for some reason, maybe the snow on those bits isn't having warmth circulated to it from the meltwater it's sitting in? If you think of snow melting on a hard surface it's often melting from underneath with an overhang around the edges, which is perhaps part of a similar process?

@John - good earthwork/snow pics, but I'd been thinking more of semi-melted. Years back after a light snow shower the flattened part of the Rudston A cursus showed up beautifully as two white stripes (over the ditches, drainage again?) running across an otherwise melted landscape - only lasted for 10 mins and of course I didn't have a camera with me, but bl**dy brilliant!

Now now old man (:face-stir
Interesting about differential melting rates on stripped archaeology...............like differential drying rates on a recently wetted surface meaning features staying as damp blobs for a bit as it drys out. Maybe linked?
Also I'm guessing wet deposits have differing thermal properties than dryer ones? Doesn't water stay warmer for longer than a solid? Guess it depends on the thermal conductivity of the substance. Or is it to do with latent heat of whatsits face.....can't really remember my thermodynamics

I know from my gliding days that tarmac heats up and keeps its heat better than the surrounding fields, and creates mini thermals.

But to get back to the photography stuff...........John, where do you see your experiments leading to is my burning question?

A greater understanding of aerial images?
Prospecting for sites before excavation?
Or the identification of individual unexcavated features on an already stripped area from the ground?
Or as an aid to show already excavated features more vividly?

Or all of the above?

I think there may have been an initial misunderstanding of your questions
'Have any readers photographed areas of an excavation outside the visible spectrum (near UV and near IR), with a normal digital camera on a tripod and appropriate filters?
Has anyone used a thermal imaging camera with any success? '

[Oxbeast]

@Kevin, that link doesn't work for me, I get a '404 not found' from their server. It sounds really interesting, and certainly up my street.

I'm pretty impressed by the photos of the open area excavation showing features under UV. That could be useful on

[John Wells]

Cool. Are those earthworks shown by shadows? Or is there some IR, UV, Thermal giggery pokery?

The top 2 images are by Jim Knowles our Group and Trust archaeologist. The details are simply shadow relief.
The third image:

is just the negative.
As with star charts and the fluorescent staining of biological specimens, it is often useful to look at an image as its negative:

[John Wells]

Do you know John whether anyone is researching how to tie the images into the stratigraphic complexity of an archaeological site?

Erik's dissertation is available online at http://munin.uit.no/handle/10037/4306

I have been concerned primarily with aerial work, hence my original questions.
I do not know of any 3D stratigraphy work....I have not looked.
We have used near vertical shots to produce 3D models of a shallow excavation in both the visible and near IR.
But as you can imagine, the walls of the excavation are a bit smeared. We had not planned making a 3D model hence only the vertical shots.
The 8.5 MB near IR model has been saved as a pdf and can be found on:
http://www.armadale.org.uk/archeoscan.htm
or directly downloaded here:
http://www.armadale.org.uk/archeoscanir02.pdf
It should be pointed out to the uninitiated, that to form one of these models using Photoscan can be simply a matter of uploading the images and about 4 clicks on a mouse! But sometimes with many images and complex sites (or artefacts) it can be something of a sod as is usual with these techniques.

One of our group members has just got his MSc with a distinction and prize for his 3D work:
http://www.topofly.com/

Our Group:
http://www.armadale.org.uk/groupmembers.htm

[John Wells]

Not sure what I'm seeing in this image (other than you in the middle). Is there a non-thermal image for comparison? Whats the dark bits (other than cold), whats the lighter rectangular bit on the left, some walls?

The image is only intended to illustrate the resolution of our thermal images and I thought that a human body (mine is now a close approximation!) was the best way to illustrated this.

Archaeologically, it is a poor shot of a smal part our first site:

http://www.armadale.org.uk/archaeology3.htm
part of a wider investigation of the Barony of Ogilface:
http://www.armadale.org.uk/archaeologyogilfaceindex.htm

If you want to see the resolution of a 140 x 140 pixel thermal camera (if I remember correctly, link to paper on http://www.armadale.org.uk/phototech03.htm) have a look at this image of Villa Rustica taken by Uli Kiesow in 2006:
? archaeoflug.de 2006
Visible left and thermal right.
This is the image that made me take up kite aerial thermography, although Uli used a microlight.

Have a look at the recent kite aerial thermogram by Larry Purcell at the foot of:
http://www.armadale.org.uk/phototech06.htm
and Larry has only just started this work!

We have had our first thermal imager for a year but have done very little work. Conditions have been atrocious this year for crop marks (including thermal ones) and safe kite work.
Our Group is working in partnership with Dave Cowley of the RCAHMS to look at a Roman site in Falkirk both within and outside the visible spectrum but this project will now only take off with next season's crop.