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For Archaeologists, New Tech for Old Sites


Published October 19, 2016 at 10:00 a.m.
Updated October 24, 2016 at 10:58 a.m.

Satellite image of Fort Ticonderoga
  • Satellite image of Fort Ticonderoga

Archaeologists dream of that "Aha!" moment, when one discovery leads to even more. Vermont state archaeologist Jess Robinson had one such moment recently. But, unlike most archaeological finds that come from digging in the ground, his "most amazing revelation" was captured from an altitude of about 12,000 feet.

On a laptop, Robinson displays two side-by-side aerial views of New York's historic Fort Ticonderoga. The first, a Google Earth satellite image, shows the 18th-century fort that was built by the French on Lake Champlain's western shore. The image includes its star-shaped bastions, outbuildings, modern roads, parking lots and surrounding vegetation.

LiDAR image of Fort Ticonderoga
  • LiDAR image of Fort Ticonderoga

Beside it is a black-and-white image created with LiDAR, a much newer surveying technology that uses lasers to generate topographic maps. LiDAR shoots and collects up to a half-million data points per second, creating a 3D map of the landscape that's accurate to within 10 centimeters. Beyond conventional satellite imagery or aerial photography, though, LiDAR can effectively "see" the forest floor's contours through the trees. When a LiDAR-equipped aircraft flies over a wooded area, some of its laser beams penetrate the canopy and bounce back. An algorithm then factors out the vegetation, creating a more accurate topo map.

The LiDAR image of Fort Ticonderoga reveals features that have been there for years but escaped notice until now — old trenches, earthworks and roads from Fort Carillon, which predated Fort Ticonderoga. Robinson emailed his findings to staff at Fort Ticonderoga, who informed him that he indeed identified previously unknown historic features. A LiDAR map of Vermont's Mount Independence in Orwell reveals batteries and other landscape features that were similarly concealed from view.

"You'd be amazed what people built, even in the early- and mid-1800s, that are almost invisible today," Robinson says. "It's just remarkable."

Archaeology is often described as the "slow science," he says. Traditionally, the work involved painstaking processes that took months or even years to interpret. But in the last few years, Vermont archaeologists have been using various new technologies, including LiDAR, to identify previously unknown cultural resources. Then, by combining them with other modern technologies such as GIS — or geographic information system software, which maps data spatially — archaeologists can now predict with greater accuracy where they're likely to discover new sites.

Aerial LiDAR is just one new tool in archaeologists' ever-expanding toolbox. Ground-based or terrestrial LiDAR is now being used to create 3D maps of historic structures, such as covered bridges, which can then be used to measure subtle changes in their structure over time — or even re-create them in the event they're destroyed by fire or flood.

LiDAR has its origins in the 1960s and '70s, notably, when the Apollo 15 space mission used a laser altimeter to map the moon's surface. But, according to Vermont Agency of Transportation archaeologist Brennan Gauthier, it wasn't until Tropical Storm Irene ravaged Vermont in August 2011 that state employees began using aerial LiDAR. They used it to survey transportation corridors and map storm damage to highway infrastructure and river banks.

Those initial LiDAR scans weren't done to identify archaeological sites per se. Still, the VTRANS archaeologist says, "It was great for me because I was able to find a lot of cool sites that no one knew about." Those included old cellar holes, stone walls, abandoned roads and even old cemeteries. Aerial LiDAR is now a standard tool that Gauthier uses for archaeological reviews, which are required on all state- and federally funded bridge and highway projects.

Recently, Gauthier used GIS software to combine LiDAR scans with historic Beers Atlas maps made in the 1860s, which plotted every road and town in Vermont. He can now shift between 19th- and 21st-century maps to see how the built landscape has changed over time.

State archaeologist Robinson and his colleagues have done something similar, using LiDAR and GIS software to determine likely travel routes of the Champlain Valley's earliest known human inhabitants.

As he explains, when archaeologists first excavated Paleo-Indian sites in Williston in the early 1990s, they didn't know yet that the Champlain Sea, which existed between 13,000 and 10,000 years ago, went that far inland — or that it was around when Paleo-Indians occupied the area. More recently, however, Robinson and his colleagues have plotted known Paleo-Indian sites and compared them to the Champlain Sea's shoreline.

Among them is the Mahan archaeological site in Williston, which contained spear points and other stone tools made from materials not native to this area. As Robinson explains, that material was sent off to a lab that used X-ray fluorescence to determine its chemical composition. His team then compared the findings to known mineral sources in the region. Robinson can now say with "a high degree of confidence" that some of the stone unearthed in Williston came from Munsungan Lake in Maine, as well as from the Hudson Valley and Pennsylvania, a region spanning about 600 miles.

The archaeologists' next challenge was to determine how the Paleo-Indians made their way from, say, interior Maine to Vermont. Robinson and his colleague, Wetherbee Dorshow from the University of New Mexico, used digital elevation models of the region — including some created with LiDAR imagery — to rank the travel routes based on slope, elevation, forest cover, water flow and other topographic features.

Then, by crunching the numbers using a GIS technique called "least-cost path analysis," they determined that the likeliest route the native peoples took to Vermont wasn't by walking overland through what are now called the Green and White mountains, as previously theorized, but by following the Champlain Sea.

"This technology shows that they could have used watercraft to get down here," Robinson says.

Other new technologies enable archaeologists to wring new data from artifacts unearthed in Vermont decades ago. Karine Taché is an assistant professor of anthropology at Queens College, City University of New York. A few years ago, she asked Robinson's permission to borrow a 2,500-year-old pottery shard that had been excavated along the Connecticut River in 1985. Her goal, Robinson recalls, was to see if she could extract lipids out of the shard to determine what its makers had cooked in it.

"She was remarkably successful," Robinson says. Taché's research, later published in the British journal Antiquity, found that the pot had been used for cooking fish. "Ten years ago," he adds, that discovery "would have been a pipe dream. Now, she's applied for another analysis ... to actually take those micro fats and radiocarbon date them" to pinpoint their age to within a 40-year time span.

John Crock, associate professor and director of the Consulting Archaeology Program at the University of Vermont, points to similar techniques that are allowing archaeologists to extract new data from old finds. In one study, which involved archaeological sites in the Caribbean, researchers extracted starch grains from cracked boiling stones — or rocks that were heated in a fire, then used to cook food — and then determined what meals they'd cooked. Another study extracted tartar from 1,000-year-old dental remains to determine what plants that human had eaten — and even how the plant had been prepared.

Still other technologies facilitate underground discoveries without ever using a shovel. Robinson points to the example set by Sarah Parcak — a professor, Egyptologist, anthropologist and 2016 winner of the $1 million TED prize. She's using crowdsourcing and satellite imagery to identify previously unknown ruins in the Egyptian desert. Eventually, Robinson would like to see Vermont use LiDAR scans, GPS and GIS software, and similar crowdsourcing to identify previously unknown cultural sites throughout the state.

As UVM's Crock points out, "The more we can do to leave things in the ground, the better. We believe that in a hundred years, we'll be better at what we do. Just like we look back a hundred years and think how barbaric archaeology was when they used pick axes and only found large objects."

Robinson agrees. Another state archaeologist — his predecessor, Giovanna Peebles, who retired in 2014 after 38 years on the job — suggests that much more remains to be discovered. As of January, Vermont had fewer than 6,000 known archaeological sites, of which 2,201 are of Native American origin. The rest are from early European settlers, old military bases such as Mount Independence and abandoned industrial sites such as the Elizabeth copper mine in Orange County.

That puts Vermont at the low end of archaeological sites per square mile nationally, Robinson points out, largely because the state is so mountainous and many areas have never been developed or studied.

But rapid technological advances in the "slow science" are highlighting the importance of proper archaeological curation for future generations. As Robinson puts it, "Who knows what tools will be available to us in 20 years?"

Find out more about how the state is using LiDAR, GIS and other mapping technologies by visiting the Vermont Center for Geographic Information booth at the Vermont Tech Jam, October 21 and 22 at the Champlain Valley Expo in Essex Junction.

The original print version of this article was headlined "Remains to Be Seen"