The Lost City of the Monkey God

by Douglas Preston

As the plane is flown in a lawnmower pattern over the jungle, the lidar device fires 125,000 infrared laser pulses a second into the jungle canopy below and records the reflections. (The laser pulses are harmless and invisible.) The time elapsed gives the exact distance from the plane to each reflection point. The lidar beam does not actually penetrate foliage. It does not “see through” anything in fact: The beam will bounce off every tiny leaf or twig. But even in the heaviest jungle cover, there are small holes in the canopy that allow a laser pulse to reach the ground and reflect back. If you lie down in the jungle and look up, you will always see flecks of sky here and there; the vast number of laser pulses allow lidar to find and exploit those little openings.