Remote aerosol sensing with an absolute calibrated double frequency lidar

A two frequency lidar system, using a Q-switched ruby laser transmitter with frequency doubler and a 52 cm dia. receiving telescope, for remote aerosol sensing up to more than 30 km altitude is described. The system includes electronic data acquisition and processing. Sufficient sensitivity for high altitude stratospheric measurements is provided by ten channel photon counting combined with range gating of the photomultiplier tube, and a mechanical chopper for rejection of the non-coherent ruby fluorescence. The system is now being absolutely calibrated by comparison between lidar backscatter profiles on the one hand, and theoretical backscatter functions calculated from experimental aerosol and aerological data, using Rayleigh and Mie scattering theories, on the other. The experimental data are acquired at mountain stations at 740, 1,800 and 3,000 m altitude by means of five stage impactors and of cable car probes and radiosondes. Examples of tropospheric lidar backscatter profiles, together with aerosol and aerological profiles, as well as stratospheric lidar measurements are presented.