Thermal Drones and Archeology

I have been pleasantly amazed at the archeology that my thermal drone reveals!

My images have shown shallowly buried walls, old prehistoric roads and racetracks, piles of lithics, and organized rocks. When those images are processed to an orthographic image then I can accurately get the gps coordinates and take a walk to find what was revealed. It is amazing!

I live on the Colorado Plateau near the Four Corners. We are generally dry and have sage brush, cedars, and scruffy grass for vegetation. Our soil does not retain a lot of moisture so it cools much faster than rocks that have been warming in the sunshine all day. Since the sun rises so early her during the summer, I have found that spring and fall are the best seasons to fly thermal missions before dawn. This past year, I would fly my missions during the day just to make sure that the drone would clear all hills, trees, and cliffs while I could see it and the terrain together. It also gave me a chance to drive the roads in daylight and find a good launch point in the daylight. Then I could feel more confident driving and launching in the dark!

Thermal images reveal objects best when the thermal contrast is greatest. When I first started flying I thought that would be about mid-day when surface things would heat up and underneath would be cold. That is not the case. Most midday pictures result in the entire surface being hot and therefore mostly white. Then I started flying just after dark. Surprisingly, foliage from trees and sage brush retain their heat long into the evening. While the dirt was starting to cool, surface vegetation obscured what was beneath, even at 10pm. Lastly, I started seeing my best results by flying about an hour before dawn. The dirt had cooled through the night, the vegetation finally released its heat, and yet, the rocks retained their warmth from the day before, even slightly underground.

The image above is from the Edge of the Cedars Museum which is built on an ancient site. The on-site archeologist was surprised and delighted to see the walls buried beneath the dirt. He knew that there was a room block, but was not aware that the walls curved around the way that they show.

The above images are of the exact same site. The one on the left was flown during the daytime and the one on the right was flown before dawn. The daytime image is far more white (hot) and the grasses and sage show white while the trees show black (cool). In the pre-dawn image the grasses and sage fade out in a light gray, leaving the fallen rock walls to show bright white (hot - still warm from the previous day’s sun).

Same thing below. They are from the exact same site and both have white as hot and black as cool. They could be negative images of one another! The right image, however, sharpens up the rock walls and by the straight lines show the shape of the structure. It was flown at about 5am, just before dawn. The left image is still has benefit as it shows the trail to and from the site, which is not seen in the nighttime image.

In summary, the information gathered by thermal imagery has surprised and delighted both us and local archeologists! In another blog, I’ll have to talk about how I gathered images with mapping missions and subsequently processed them. Stay tuned!