Scientists have discovered a lost Mayan city, hidden for centuries by the dense jungle of Mexico, using LiDAR.
What is LiDAR?
LiDAR, or Light Detection and Ranging, is a remote sensing technology that uses light in the form of a pulsed laser to measure the range (or range) of a sensor, usually mounted on an aircraft, over the Earth’s surface. LiDAR data can be used to create high-resolution 3-D models of land elevation with an accuracy of up to 10 cm, according to the US Geological Survey.
How does LiDAR work?
LiDAR instrumentation includes a laser, a scanner, and a GPS receiver. A fast-firing laser travels down the ground where it hits vegetation, structure, and various topographic features. This light is reflected or scattered, and recorded by a LiDAR sensor.
The system calculates the travel time of the two-way pulses to reach the distance between the object and the sensor. It processes this information through Global Positioning System (GPS) and Inertial Measurement System (IMS) data, to create a map of the earth’s elevation.
LiDAR data is initially collected as a “point cloud” of all the individual points that are reflected on all surfaces, including buildings and vegetation. But specifying how much light energy is returned to the sensor allows more identification of various features, such as vegetation, structures, etc. For example, tree canopies, no matter how dense, allow some light to pass through and hit the ground. .
LiDAR data can be further enhanced to produce what scientists call a “bare-earth” Digital Elevation Model, where buildings and vegetation are removed.
Why is LiDAR so useful for archaeologists?
LiDAR is used to generate accurate, three-dimensional information about the shape of the Earth and its surface features. This is obviously very useful information for geographers, policy makers, conservationists, and engineers. However, in recent years, LiDAR has also shown potential as a tool for finding fossils.
“For a very long time, our sample size of the Maya civilization was a few hundred square kilometers,” said Luke Auld-Thomas, lead author of the latest study published in the journal Antiquity, in a press release. “That sample was hard won by the archaeologists who carefully walked every square meter, cutting the grass with a machete, to see if they were standing on top of a pile of stones that might have been a human home 1,500 years ago,” he said.
But LiDAR allows researchers to study very large areas of the world from the comfort of a home or lab. Auld-Thomas used publicly available LiDAR data taken from a forest monitoring project in 2013 to locate a town he named Valeriana in the Campeche region of Mexico.
The city “has all the signs of a political capital of the Ancient Maya: many walled plazas connected by a wide road, temple towers, a football field, a reservoir built to block an arroyo (seasonal water river), and an architectural arrangement that may… indicate a date of establishment before 150 CE”.
He hopes that his discovery will help reveal some of the civilization’s hidden habitats. He said: “We found a large city with pyramids near the only local highway, near a city where people have been farming in the ruins for years. The government never knew about it, the scientific community never knew about it… there is a lot more to be discovered.”