One of my favorite authors is Douglas Preston, co-author of one of my favorite ongoing book series about FBI ‘Agent Pendergast’. To my surprise, Preston not only wrote another, unrelated book, on “The Lost City of the Monkey God”. During the research for this book, he accompanied an expedition to the jungles of east Honduras with a team searching for pre-Columbian ruins.
What intrigued me, as an electrical engineer, were the technical aspects of light detection and ranging (LIDAR) techniques that were able to discover and map a densely covered jungle area canopy. This jungle was virtually impossible to explore on the ground due to dense foliage which had to be hacked inch-by-inch by the explorers. This would have taken forever, and add to this a violent rebel presence in the area as well, and the task seemed impossible.
Initially, only RADAR and satellite imaging were technologies that could do such mapping, but these could not penetrate through such a dense jungle canopy. However, LIDAR could give a resolution of three feet, even under a jungle canopy. These LIDAR units shoot thousands of laser bursts per second, through the tiny openings in the jungle foliage, creating a detailed topological map with the magic of technology.
How LIDAR Does It
The LIDAR is flown on an old Cessna Skymaster with a special flight plan that would allow for laser penetration of the jungle canopy. These flight plans scan every square meter of the rainforest from several angles, and are referenced against a GPS base station within 100 km of the area being searched to provide accurate data of the jungle floor.
Normally, the LIDAR is flown about 600 meters above ground level at a speed of 60 meters/second. The laser fires at a rate of 125 thousand times per second, shining light onto a footprint half a meter in diameter.
The process took two-weeks, with seven flights that totaled 32.1 hours with 8.4 hours of flight time with the laser on. A total of 3.5 billion LASER pulses were fired over an area of 122.8 km². Only 87 Million actual ground returns were classified (Most reflected off the dense canopy of vegetation). These returns were processed with a specialized computer algorithm that was able to stitch all the data together to make an image that brought out the contours of an ancient civilization’s remains. The most common was a set of shaded relief images that represent the surface terrain stripped of the dense vegetation!
Ultimately, the next steps in this kind of imaging would be the use of unmanned aerial vehicles (UAVs) equipped with LIDAR technology. This has the benefit of being much less expensive than a manned plane, allowing researchers to cover more ground at the same cost, or simply used as a preliminary investigation before bringing out the big guns. Alternatively, a UAV could canvas the same area repeatedly, generating better quality data.
The use of LIDAR has the potential to revolutionize the field of archeology and with that the understanding of ancient cultures. LIDAR-equipped planes have already revealed Mayan ruins in Guatemala and shown previously undiscovered cities in the Amazon. With these targets in mind, field archaeologists have their plates full, and we’re approaching a revolution in the field.