Lidar is an acronym that stands for “light detection and ranging” [LIght, Ddetection, And, Ranging].
The first use was to calculate distance by measuring time for a signal to return.
The initial intent was to track satellites, but the actual first applications were for meteorology, the study of measurement, to measure clouds and pollution. Soon after, it was used to map the surface of the moon.
Lidar uses ultraviolet, visible, or near infrared light to image objects.
A narrow laser beam can map physical features with high resolutions, such as 30cm resultion of a terrain from an aircraft.
NASA uses lidar as their key technology for enabling autonomous precision safe landing for lunar vehicles.
Digital lidar sensors use semiconductor-based lasers and detectors that allow for the lidar system to be integrated into a single application specific integrated circuit (ASIC). These semiconductor detectors are based on single photon avalanche diode (SPAD) detectors which are able to count individual photons received from the laser emitter. Legacy analog lidar sensors, including both MEMS and other spinning sensors, use APDs or SiPM detectors which measure the strength of the light signal, but cannot count individual photons. Legacy analog detectors measure intensity less precisely, need regular recalibration, and are highly susceptible to failure from outdoor use.