The optical setup of an airborne differential absorption lidar based on optical heterody-ne detection of topographic backscattering of CW tunable CO2 lasers will be shown. A simplified arrangement that takes advantage of the internal ampliiicattion of the backscattered and Doppler shifted light by the operating lasers makes excellent separation of the wavelength channels possible. As a result the optomechanical system is highly compact and minimum number of elements are used; e.g. all the necessary optical signals measured by a single detector are electronically separated. The lidar is used for detection of molecular pollutants in the atmosphere from an airborne platform. False information rejection is carried out by simultaneous processing of differential absorption signal and fluctuation characteristics of the signal originating from scattering from the random rough topographic surface.
"Airborne Differential Absorption Lidar", Proc. SPIE 0889, Airborne and Spaceborne Lasers for Terrestrial Geophysical Sensing, (12 April 1988); doi: 10.1117/12.944262; https://doi.org/10.1117/12.944262