Chirp-induced bias in velocity measurements by a coherent Doppler CO₂ lidar

Radial wind velocity measurements by a pulsed CO₂ Doppler lidar may be biased even in stationary atmospheric conditions. The authors show it is due to random speckle fluctuations of the backscattered signal and is related to the dissymmetry of the transmitted laser pulse periodogram. A procedure is proposed to correct for the bias on a shot-to-shot basis when a pulse-pair mean-frequency estimator is used for processing. The procedure is validated on simulated and actual lidar signals.