Characterization of pulsed coherent Doppler LIDAR with the speckle effect

Abstract

The relationships among heterodyne efficiency γ, number of speckle cells M, and the ratio of receiver area to coherence area SR/SC for a pulsed coherent laser radar (CLR) are written through the use of mutual coherence functions. It is shown that numerical values for SR/SC that follow Goodman’s definition [J. W. Goodman, in Laser Speckles and Related Phenomena, J. C. Dainty, ed. (Springer-Verlag, Berlin, 1975), pp. 9–75] or that are obtained through the use of a transverse-field coherence length agree. In the frame of the Gaussian model proposed by Frehlich and Kavaya [Appl. Opt. 30, 5325 (1991)] a new equation is derived: M = (1 + SR/SC). This equation agrees with our experimental results. Our theoretical analysis shows that the number of speckle cells for an optimal monostatic CLR system is M ~ 4. An experiment has been conducted with a ground-based pulsed CO2 LIDAR and remote hard targets to study the probability density function of LIDAR returns as a function of M and to study the dependence of M on SR/SC. An assessment of CLR performance through the use of M or the collecting aperture SR is discussed.