Sat, Sep 24, 2016 - Page 9 News List

Laser scans unveil network of ancient cities in Cambodia

Lidar technology shows 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

By Julia Wallace  /  By Julia Wallace NY Times News Service, SIEM REAP, Cambodia

Illustration: Constance Chou

For decades, archeologists 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 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.

However, this year, archeologists 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, Mackey, his eyes glued to the ground, pounced on a shard of celadon 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 archeologist it’s really interesting that we have this representation of cultural activity,” Mackey said.

He and Leaksmy are part of a consortium of academics called the Cambodian Archaeological Lidar Initiative, or CALI, which uses a technology known as lidar to shoot quick 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 Mackey, a 14-year veteran of fieldwork in Cambodia, noted that before lidar’s availability, an accurate ground survey of archeological features in the 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,” Mackey said.

CALI’s helicopters flew for 86 hours in March and April last year over 1,910km2, with Buddhist monks blessing the lidar sensors before takeoff. The data generated during the flights, based on about 40 billion individual measurements, is being verified and made public.

“We had hit a roadblock in terms of technology until recently,” said Damian Evans, the archeologist 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, Evans said, has been an unprecedented new understanding of 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 the Angkorians used to control the flow of water.

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