Mapping Marvel: Lost cities found

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GPS and airborne light detection and ranging (lidar) have revolutionized archaeology. In just a little more than a decade, dozens of previously hidden cities and settlements have been discovered under heavy tree canopy and in other terrain. Many of the sites are in difficult-to-access areas, such as high atop mountains, in vast deserts, or enclosed in thick, nearly impenetrable foliage. Many were only the stuff of legend.

Others are right under our feet. In 2018, early settlements were uncovered in New England, including now-abandoned walls, roads and building foundations.

With the development of lidar, archaeologists gained perhaps their most powerful tool since carbon dating. Lidar began as a million-dollar classified technology. Now lidar units are small enough to attach to unmanned aerial vehicles (UAVs).

Lidar devices send more than 100,000 laser pulses to the ground every second and use their return times to calculate precise elevation data that allow researchers to build three-dimensional maps of a landscape, while GPS receivers provide its coordinates. Lidar fly-overs have revealed ancient cities, temples, causeways, irrigation systems and other structures, which are then ground-truthed by excavation teams.

“Lidar has completely changed the way we survey ancient Maya cities and what we can know about them, and it is a thousand times better than [what we used] before,” Francisco Estrada-Belli told GPS World. Estrada-Belli is a research professor at Tulane University’s Middle American Research Institute.

The application of lidar to archaeology began in 2009, when NASA sponsored a remote-sensing project that showed lidar’s usefulness below the forest canopy. The project revealed the surprisingly vast scope of Caracol, the largest Mayan archaeological site in Belize. Urban Caracol maintained a population of more than 100,000 people with an immense agricultural field system and elaborate city planning.

Since then, lidar has been used the world over to uncover buried secrets from early Roman fortifications in Italy to landscape changes from World War I. Just this August, lidar unearthed sobering evidence of a massacre by Nazi Germany in Poland during World War II.

Image: F. Estada-Belli/Pacunam Lidar InitiativePhoto:

A landmark project in Guatemala illustrates the benefits of lidar. The ancient city of Tikal was one of the best-mapped regions of the Mayan world, but the Pacunam Lidar Initiative quintupled the amount of mapping done in 50 years in a single summer, with 61,000 structures found in an 810-square-mile area invisible to the naked eye because of overgrown vegetation. What experts had mistaken for unusable swampland, for instance, had actually been farmland, crisscrossed with canals. The area may have been home to a population of up to 10 million people. Results were published in Science in 2018.