Archaeologists spend much of their professional lives in holes, digging deep underground to discover the remains of ancient communities and cultures. But now, some of them are taking to the skies—with a little help from drones. By outfitting these unmanned craft with thermal cameras, archaeologists have discovered a new and affordable way of seeing what’s underground while flying high above it.
Thermal imaging has been “the unexplored frontier” in archaeology for a long time, says Jesse Casana, an archaeologist at the University of Arkansas, Fayetteville. The idea behind the technique is simple: Over the course of a day and a night, different parts of a landscape heat up and cool down at different rates. Buried stones, for example, tend to retain heat longer than dry soil around them does. That means that in the early morning, the stones will be much warmer than the surrounding earth. Those temperature differences are invisible to our eyes, but a thermal camera—which detects infrared light, otherwise known as heat—can easily record and reveal them. And if those buried stones happen to be the remains of ancient buildings, that camera has just taken a picture of a lost settlement without digging a single hole.
But how do you get a thermal camera up in the air to take those pictures? In the past, archaeologists have tried everything from small planes and helicopters to hot air balloons and kites. Casana recalls that one team even sent a graduate student up in a powered parachute—basically a flying go-kart—to snap thermal pictures of a site while leaning over the side. They got “amazing results,” but the technique was time-consuming, expensive, and dangerous, Casana says. So he started thinking about alternatives. What kind of contraption could fly a thermal camera over a large area without much help from humans on the ground—and do it for not very much money? Then it hit him: a drone.
Drones, otherwise known as unmanned aerial vehicles (UAVs), are becoming increasingly popular in many kinds of scientific research. They can fly for about 15 minutes on their own, covering much larger areas than a balloon or kite can. Plus, they are cheap (and getting cheaper); anyone can buy a kit and build their own UAV for just a few hundred dollars. All Casana needed to do was strap a thermal camera onto one, program a flight plan over an archaeological site, and wait for its buried features to be revealed.
Casana took his drone setup to a known ancient settlement site in northern New Mexico called Blue J. Occupied from about 600 C.E to 1150 C.E. by people known as Ancestral Puebloans, Blue J was populated at the same time as sites around Chaco Canyon, about 70 kilometers to the north. But unlike better studied Ancestral Puebloan settlements, Blue J is buried under a meter of desert sand. Most of its ancient stone architecture is obscured, and it’s hard for archaeologists to even know where to start digging.
By sending the thermal camera on four, 11-minute drone flights over Blue J, each at a different time of day, Casana and his team revealed many of the community’s buried structures. Not only did the thermal images accurately record most of the known buildings at Blue J, but they also revealed that some of these structures were much larger than archaeologists previously thought, the researchers report in this month’s Journal of Archaeological Science. Thanks to the drone, the team may have even spotted a great kiva, a type of underground ceremonial structure found in most Ancestral Puebloan communities but, strangely, not yet in Blue J. That’s the kind of discovery that can help future teams of archaeologists pinpoint the most promising places to begin their excavations, Casana says.
Drones outfitted with imaging technology such as thermal cameras have “become an amazing tool for identifying archaeological sites and figuring out where excavations should take place,” agrees Austin Hill, a research scientist at the University of Connecticut, Storrs, who has used UAVs for surveys of archaeological sites in the Middle East and was not involved in the Blue J work. There’s just one problem, he says: Drones are “prone to falling out of the sky.” UAVs are still a relatively new technology, prone to glitches and failures. There’s “a steep learning curve” just to get to the point where your drone doesn’t crash every time you try to fly it, Casana says. Luckily, replacement parts are cheap, and like many young technologies, UAVs are improving rapidly. Soon, they may be as indispensable to archaeologists as shovels and trowels—if not quite as easy to use.