American Scientist

To the Editors:

I was interested to read about Anabel Ford’s experience using LIDAR at the Maya settlement El Pilar (“The Enduring Legacy of the Maya,” First Person, May–June). I am not an archaeologist, but I have spent more than two decades applying airborne and ground-based LIDAR to the mapping of a variety of terrains—including beaches, forests, snowpack, and flood waters—and archaeological sites, including many hidden beneath the rainforests of Central American countries. (See “Estimating Ancient Populations by Aerial Survey,” January–February 2019.)

Over the course of my career, manufacturers have advanced their LIDAR systems from a few thousand pulses per second to a million or more pulses per second, as well as increasing the number of reflections recorded from each pulse, greatly improving the resolution and accuracy of maps that can be derived from the LIDAR point clouds. Obtaining research-quality LIDAR observations still depends on careful calibration of the LIDAR unit, accurate aircraft trajectories derived from local GPS base stations, and adequate overlapping of the LIDAR swaths to enable accurate classification and filtering of the point clouds.

Hundreds of archaeologists could spend their entire careers mapping the rainforests of Central America and still miss thousands of important ruins, including major cities, and their connections. The sooner the entire region is mapped with research-quality LIDAR, the better.

William (Bill) E. Carter
Washington, PA