The optical analog of radar. The term lidar is an acronym for light detection and ranging. Lidar systems employ intense pulses of light, typically generated by lasers, and large telescopes and sensitive optical detectors to receive the reflected pulses. They are most commonly used to measure the composition and structure of the atmosphere. The very narrow beamwidth, narrow linewidth, and ultrashort pulses of the laser make it possible to optically probe the atmosphere with exceptional sensitivity and resolution. When used to measure the range and velocity of hard targets, lidars are usually called laser ranging systems or laser radars.