Airborne lidar LEANDRE II for water-vapor profiling in the troposphere. I.System description

The airborne differential absorption lidar LEANDRE II, developed for profil ing tropospheric water-vapor mixing ratios, is described. The emitter is a flash-lamp-pumped alexandrite laser, which operates in a double-pulse, dual -wavelength mode in the 727-736 nm spectral domain. Two 50-mJ successive on -line and off-line pulses with an output linewidth of 2.4 X 10(-2) cm(-1) a nd a spectral purity larger than 99.99% are emitted at a 50-mus time interv al. The spectral positioning is controlled in real time by a wavemeter with an absolute accuracy of 5 X 10(-3) cm(-1). The receiver is a 30-cm apertur e telescope with a 3.5-mrad field of view and a l-nm filter bandwidth. Thes e instrument characteristics are defined for measuring the water-vapor mixi ng ratio with an accuracy better than 0.5 g kg(-1) in the first 5 km of the atmosphere with a range resolution of 300 m, integration on 100 shots, and an instrumental systematic error of less than 2%. The sensitivity study an d first results are presented in part II [Appl. Opt. 40, 3462-3475 (2001)]. . (C) 2001 Optical Society of America.