ENFIELD, N.H. – Scanning an empty field that once housed a Shaker village in New Hampshire, Jesse Casana had come in search of the foundations of stone buildings, long-forgotten roadway and other remnants of this community dating to the 1790s.
But instead of a trowel and shovel, Casana and his Dartmouth College colleague Chad Hill are using a drone equipped with a thermal-imaging camera and mapping instruments. The camera can identify remnants of buildings and other structures up to several feet below the surface, since the temperature of that brick or stone material is often warmer than the soil around it. And by using the drone, the researchers can survey an area in minutes that might take months with traditional methods.
“If you look, you see a flat field, but below it there are big stone walls. There are cellars. There is a big old well, all kinds of stuff you can't see on the ground,” Casana said of a community that once housed nearly 100 buildings but was sold in the 1920s and is now an outdoor history museum. “Those things have different thermal properties. If you capture an image at the right moment, you can see it – which is amazing.”
Archaeologists have for decades have used aerial photography and more recently satellite imagery and data from laser sensors known as Lidar to map and discover new sites. The field is further transforming with the emergence of cheap drones, resulting in several significant discoveries in Asia, South America and the Middle East, including a massive man-made stone platform spotted last year hidden under sand in the ancient city of Petra in Jordan.
Casana and Hill have taken the process a step further by adding a thermal-imaging camera.
They have found structures around an Islamic fort in Qatar and used the drone and camera in October to identify a circular structure at a prehistoric site connected to Native Americans near Joliet, Illinois.
So far, Casana said, the camera technology has proved a success at arid locations without a lot of vegetation and where the structures are near the surface. It has been more challenging or nearly useless at sites with forest cover or, in the case of Cyprus, where there wasn't a big difference in temperature between the structures and surrounding soil.
“I would say it could be potentially game-changing if people would adopt it,” Casana said.
Mark Schurr, a University of Notre Dame anthropology professor who is co-directing the Illinois dig with his colleague Madeleine McLeester, said he is optimistic Casana's discovery would offer clues into a society that lived here as far back as 17th century before the French arrived.
The site is now home to the Midewin National Tallgrass Prairie, the only federal prairie reserve east of the Mississippi. Researchers are hoping to better understand things like trade networks, agriculture practices and their involvement in warfare.
“Every time we get a new imaging technique that does not include excavation – which is expensive and destructive – it's always a plus. It allows us to see new things,” Schurr said.