What did past civilizations leave behind? For archaeologists, that question can be difficult to answer. Remnants of buildings and other sites can be almost impossible to spot. Blame the ravages of time and nature, which can cover old walls and foundations in trees, vegetation, water, soil, and more.

Then turn to LiDAR, one of archaeology’s most exciting modern tools. Light detection and ranging, or LiDAR, has changed the face of archaeology by making it possible to measure and map objects and structures that might otherwise remain hidden.

Mapping with light Lidar, or “light detection and ranging” technology, directs hundreds of thousands of pulses of light toward the ground. 2,000 ft constant altitude above ground level A canopy B ground ruins Cloud creation In forested locations, most beams of light reflect off the forest canopy (A, above); a few reach the ground (B) and reflect back through the canopy. Recording how long it takes the light to return to the device produces a “point cloud.” Point Cloud MANUEL CANALES, NGM STAFF

Modern LiDAR relies on laser sensors that are deployed from the air or via handheld units. As lasers shine on the area to be mapped, they emit brief pulses of light. The amount of time it takes for those pulses to reflect back to the instrument is measured, and each measurement is plotted using GPS. Computers then use that data to construct a 3-D map of the area.

Adapting military tech

One of LiDAR’s strengths is how well it can pinpoint tiny surface anomalies that indicate small sites like graves or big ones like sunken cities. But LiDAR has its limitations: It can’t reach beneath the ground, and trees in densely wooded areas can sometimes cause features to be missed.

Still, its accuracy is prized by archaeologists, who use it to map topography, plan excavations, and spot archaeological sites they’d never be able to see with the naked eye. It is relatively quick and inexpensive compared to archaeological excavations, and can offer a high-level view not accessible to researchers who focus on just a few sites on the ground.

The technology was invented for military use, but was first applied widely by meteorologists intent on studying clouds. The first LiDAR prototype was built in 1961 by Hughes Aircraft Company, which had built the first laser a year earlier. One of the earliest beneficiaries of LiDAR was the United States’ space program; the technology was used to map the moon during the 1971 Apollo 15 mission. Today, LiDAR is more down to earth, and is used to find archaeological clues both on the surface and in the water.

“Archaeology revolution”

Remote sensing has been credited with an “archaeology revolution” that is shifting the way researchers think about their work. In the early 2010s, archaeologists looking for evidence of hard-to-find Maya sites were astonished when LiDAR revealed a lost Maya city.

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In another case, researchers used LiDAR to spot more than 20,000 archaeological features of a seemingly minor site in Mexico that actually had been home to an ancient city. “In 45 minutes of flying, the LiDAR team accomplished a decade’s worth of archaeological survey,” said anthropologist Christopher Fisher in a release. Bathymetric LiDAR even revealed a Roman villa in Croatia.