Jesse Casana has extensive experience using UAS for research and exploration purposes, domestically and abroad. He recently worked with John Kanter of the University of Florida on archaeology projects using unmanned aircraft. Increasing Human Potential recently had the opportunity to talk to Jesse and learn more about his most recent projects and research.
Earlier this year, you and your team used UAS to conduct an archaeological survey in the New Mexican desert. While there, you found remnants of an ancient Pueblo society. What brought you to New Mexico, and what specifically were you hoping to find?
Jesse Casana: I had received an NEH [National Endowment of the Humanities] Digital Humanities grant to develop methods for archaeological aerial thermography and was looking for potential test sites in different environments and with different kinds of archaeological features. I thought his site seemed well suited to the project, given its location in an arid environment and the relatively shallow stone architecture. So I proposed the project to John, who was enthusiastic, so we took it from there.
This discovery was made in large part due to each of your complementing areas of expertise. Can you tell us a bit about your background and what drew you to this particular mission?
I work mostly in the Middle East — previously in Syria, Turkey, Cyprus and the UAE, currently in Iraqi Kurdistan — but a big part of my research involves geospatial technologies in archaeology. I do a lot of work with satellite and aerial remote sensing as well as ground-based geophysics. The emergence in the past few years of new civilian drone technology combined with rapid advanced in photogrammetric processing software, which is what enables production of maps and 3-D models from drone-acquired imager, have led to a huge surge of interest in these technologies by archaeologists. For my part, I was, and remain, quite interested in exploring the potential of these technologies to do more than just take pictures, but to really reveal things we can’t otherwise see. Thermal imaging is a great way to do that, but there are other possibilities with additional sensors, such as NIR [near infrared], lidar, etc.
Based on each of your previous research experiences, what benefits were UAS able to provide in this survey relative to traditional survey methods? What advantages did they offer compared to their manned counterparts?
First of all, most archaeological sites are visible at the surface but typically are only evidenced by surface concentrations of artifacts and building debris. If we want to see below the surface, excavation is the most obvious and oldest method, but it is a painstakingly slow process as well as destructive one — we can’t ever re-dig a trench. We do it once, and that’s that. So in the past couple decades, a suite of technologies have been increasingly utilized by archaeologists to see below the ground in nondestructive ways. These techniques, collectively sometimes called archaeological geophysics, include things like magnetic gradiometry, ground-penetrating radar and electrical resistivity. Each method can “see” different archaeological phenomena. Magnetics is good for finding things that have been burned or things with magnetic proprieties like ferrous metals. Radar is good for finding things that have a high contrast with surrounding soil in terms of the degree to which they reflect or absorb radar waves, like stone buried in soil for example. These methods can be great, but some won’t work at all on certain sites. At Blue J and many sites in the Southwest, the type of soil and the stone used in building construction often have very weak if any magnetic properties, making them very difficult to detect with magnetic gradiometry. Electrical resistivity relies on passing a current through soil but does not work at all in arid environments, owing to the lack of moisture in the soil. Radar could potentially work, but it requires the radar antenna to be dragged across the ground surface in a series of closely spaced transects, and that would be almost impossible to do on a site with lots of rocks, thorny plants and other obstacles that are common on southwestern sites. Also, with all these methods even experienced operators can only cover one to two hectares per day at the most. Aerial surveys like ours on the other hand can cover vastly larger areas in a matter of minutes. We could easily survey several hundred hectares in a day. For archaeological purposes, imagery needs to be very high resolution, since the things we see are pretty small. Thermal cameras, because of the sensor technology, have very coarse spatial resolution. The best cameras civilians can buy are 640-by-512 pixels. This means that in order to see archaeological features, which might be less than half a meter, we need to fly very close to the ground, much closer than would be possible in a manned aircraft. But we also need to be able to fly over the site multiple times during the day or night … something that would be extremely expensive if you were doing it using a helicopter or something. I mean, a helicopter would be awesome, but I don’t own one and have never known an archaeologist who did.
The pairing of UAS with thermal technology is relatively new. Can you walk us through how it works and how it can be beneficial?
Archaeological thermography is essentially another tool in our kit to see what is on or below the surface nondestructively but is the least used and most poorly understood of all the major methods. People have experimented with it and speculated it might be useful since the 1970s, but until now it has been cost prohibitive to get a thermal camera with sufficiently high resolution in the air at the right time of day above an archaeological site. Our data demonstrate clearly that thermal imaging is highly time sensitive, such that images collected just an hour or so apart of the same site can be wildly different in what they reveal. In theory, buildings or other archaeological features that are below ground might retain, transmit and emit heat — really just a long wavelength of light — at different rates than surrounding soil. Experimental data suggest we should be able to detect these differences for features buried a half meter below ground or more. You can think of a buried stone wall, heating and cooling through the course of a day and night at a different rate than surrounding soil. If you were to take a thermal image at the right time of day or night, when those differences are most pronounced, you should be able to see the wall “glowing” at the surface. That is the basic idea. It turns out that collecting imagery during the day probably does not work well, because reflection of thermal radiation from the sun off the ground tends to wash out minor differences caused by buried features. Night-acquired imagery is much better, when, after the sun has set, we can image differential cooling of the ground and things buried in it. On a site where the features are amenable to detection this way, imaged at the best time of the night, we could theoretically map subsurface and near-surface archaeological remains over vast areas, and we can do so on sites like Blue J that would be really tough to survey by any other method.
How did that help with this most recent research in New Mexico? What were you able to find?
We were able to see almost every house compound that they had mapped at the site and could map the architectural organization of these compounds in many cases. We also found a subterranean circular feature that could be a great kiva [a Pueblo Indian ceremonial structure].
You have done similar archeological research using unmanned aircraft in Cyprus and Iraq. Can you tell us about those experiences? How did that research differ or prepare you for this work in New Mexico?
Yes, I’ve been flying these things various places in the world over the past couple years. We had several surveys in the U.S. prior to New Mexico, at Cahokia, Illinoise, and Arzberger, South Dakota, but neither worked very well, mostly because we kept crashing the drone. Since Blue J, we have done a lot more work on this stuff both in the U.S. and abroad. In Cyprus, data collection was perfect, but we did it at a very arid time of year so the results were not great. I think that some soil moisture is important for highlighting differences. In Iraq last summer, the drone and camera were taken by airport security and I never was able to get in into the country. Actually in Cyprus we were detained by the police for a night and the equipment was taken, but they gave it back eventually. There are always adventures like that when flying drones.
What does that future hold for you and UAS? Do you have any other exciting research projects planned? What would you like to do next?
I see a lot of new possibilities. I am working on several things these days, including new methods for acquisition and especially processing of thermal data. We also built a test site here at the university farms with fake buried walls and ditches so that we could experiment with collection of thermal imagery in a controlled environment. I’m planning another survey up in South Dakota this summer and will hopefully be doing it in Iraq and Turkey this coming fall.