By JULIA WALLACESEPT.
SIEM REAP, CAMBODIA — For decades, archaeologists here kept their eyes on the ground as they tramped through thick jungle, rice paddies and buffalo grazing fields, emerald green and soft with mud during the monsoon season.
They spent entire careers trying to spot mounds or depressions in the earth that would allow them to map even small parts of Angkor, the urban center at the heart of the Khmer empire, which covered a vast region of what is now Cambodia, Thailand, Vietnam and Laos from roughly A.D. 802 to 1431. In modern times, little material evidence existed beyond a network of monumental stone temples, including the famed Angkor Wat, and the sprawling settlements that presumably fanned out around the temples long since swallowed up by the jungle.
But earlier this year, the archaeologists Shaun Mackey and Kong Leaksmy were armed with a portable GPS device containing data from an aerial survey of the area that is changing the way Angkor is studied. The device led them straight to a field littered with clods of earth and shot through with tractor marks. It looked to the naked eye like an ordinary patch of dirt, but the aerial data had identified it as a site of interest, a mounded embankment where the ancestors of today’s Cambodians might have altered the landscape to build homes.
Almost immediately after stepping onto the field, Mr. Mackey, his eyes glued to the ground, pounced on a shard ofceladon pottery. Soon the team had turned up a small trove of potsherds and began taking copious notes.
“It’s not sexy, like a temple, but for an archaeologist it’s really interesting that we have this representation of cultural activity,” he said. He and Ms. Kong Leaksmy are part of a consortium of scholars called the Cambodian Archaeological Lidar Initiative (CALI), which uses a technology known as lidar to shoot ultraquick pulses of light at the ground from lasers mounted on helicopters. The way they bounce back can show the presence of subtle gradations in the landscape, indicating places where past civilizations altered their environment, even if buried beneath thick vegetation or other obstructions.
The soft-spoken, fedora-clad Mr. Mackey, a 14-year veteran of fieldwork here, noted that before lidar’s availability, an accurate ground survey of archaeological features in the Cambodian landscape entailed years or even decades of work.
“We’ve all spent hours getting clawed and shredded by bamboo forests with thorns or dense scrub and bush, in the hope that we might find something,” Mr. Mackey said.
CALI’s helicopters flew for 86 hours in March and April of 2015 over 1,910 square kilometers, or 737 square miles, with Buddhist monks blessing the lidar sensors before takeoff. The data generated during the flights, based on roughly 40 billion individual measurements, is now being verified and made public.
“We had hit a roadblock in terms of technology until recently,” said Damian Evans, the archaeologist who heads the initiative. “The vegetation was obscuring these parts of Angkor and other monumental sites. The lidar allowed us to see through the vegetation.”
The result, Dr. Evans said, has been an unprecedented new understandingof what the Khmer empire looked like at the apex of its power, with lidar-generated maps revealing an intricate urban landscape stretching across several provinces of modern-day Cambodia, along with a sophisticated network of canals, earthworks and dams that the Angkorians used to control the flow of water.
“It is pretty amazing,” he said. “The larger the temples are, the larger the urban infrastructure around it is likely to be, so they weren’t lost, in the sense that we assumed that they must be there. But, of course, that is an entirely different thing from being able to see it in incredible detail and how it works and how it functioned, how it evolved, the morphology of these places.”
The group is now using the maps to make more targeted excursions into the field, “ground-truthing” the lidar data to ensure that it is accurate and to determine where digging might be useful. On a recent mission, Mr. Mackey barreled down a freshly paved road in a pickup truck driven by Ms. Kong Leaksmy.
Although the Khmer empire’s great stone monuments have endured for centuries, spawning a $60-million-a-year tourism industry and preserving information about the dynasty of god-kings who ordered their construction, the stuff of everyday life at Angkor, made from wood, mud, thatch and brick, has long since rotted away in the hot and humid climate. Almost nothing has been known about the lives of those who built the temples and served its rulers — who they were, how they lived, what they believed.
David Chandler, a professor emeritus at Monash University in Melbourne, Australia, and a leading historian of Cambodia, said the new lidar data was particularly exciting because it was providing more information than ever about how ordinary people lived in the Khmer empire.
Historians had assumed that the residents of Angkor existed — “these temples certainly didn’t get built by themselves,” Dr. Chandler said — and they had cobbled together some understanding of the area’s population through inscriptions, notes from a Chinese diplomat who visited Angkor, and a few other sparse clues. Dr. Chandler compares the process to trying to understand American history from a small collection of obituaries and Fourth of July speeches.