Airborne laser scanning

Laser scanning, often denoted lidar (light detection and ranging), is a surveying method that measures distance to a target by illuminating the target with coherent light of a single wavelength, often 1,064 nm. When the lidar device is mounted on an airborne platform (e.g., helicopter or airplane), the device is normally sweeping across the flight direction in order to cover a strip with a width underneath the trajectory. The scan angles can e.g. be  ±20 degrees off-nadir. The reflected signal is filtered in order to identify one or several discrete targets that caused the reflections. The result is denoted point cloud and gives a good representation of the underlying targets, e.g., a forest, that can be visualized in 3D. Entire waveforms can be stored and post-processed to derive additional information when necessary.