Lidar air pollution monitoring. The laser beam of a Lidar unit being used to study air pollutants over Albuquerque, USA. Lidar (LIght Detection And Ranging) uses a series of very short laser pulses which are sent into the atmosphere. Any reflected light is collected by a telescope and analysed by computers. Scanning the laser across the sky gives a 2- or 3-dimensional map of the pollutant concentration. By studying the backscatter of different wavelengths of laser, the chemistry of pollutant aerosols or particles may be identified. Lidar may also be used to study volcanic plumes, temperatures and atmospheric dynamics.