Spectral diversity technique for heterodyne Doppler lidar that uses hard target returns

A two-mode CO, laser is used as transmitter in a 10-mu m heterodyne Doppler lidar (HDL) to take advantage of a spectral diversity technique, i.e., independent realizations obtained with different spectral components. The objective is to improve the properties (i.e., less variancefofpower returns from a hard target. The statistical properties are presented first for a broad-spectrum laser transmitter and then for a two-mode laser transmitter. The experimental results for a cooperative diffuse hard target show that the return signals for a frequency separation Delta f = 15 MHz can be decorrelated, depending on the angle of incidence and the target roughness. The experimental results show that the spectral diversity technique improves the performance of the HDL. (C) 2000 Optical Society of America OCIS codes: 010.3640, 030.6140, 040.2840, 280.1910, 290.5880.