Analytical empirical expressions of the transverse coherence properties for monostatic and bistatic lidars in the presence of moderate atmospheric refractive-index turbulence

There have been many analyses of the reduction of lidar system efficiency i n bistatic geometry caused by beam spreading and by fluctuations along the two paths generated by refractive-index turbulence. Although these studies have led to simple, approximate results that provide a reliable basis for p reliminary assessment of lidar performance, they do not apply to monostatic lidars. For such systems, calculations and numerical simulations predict a n enhanced coherence for the backscattered field. However, to the authors' knowledge, a simple analytical mathematical framework for diagnosing the ef fects of refractive-index turbulence on the performance of both bistatic an d monostatic coherent lidars does not exist. Here analytical empirical expr essions for the transverse coherence variables and the heterodyne intensity are derived for bistatic and monostatic lidars as a function of moderate a tmospheric refractive-index turbulence within the framework of the Gaussian -beam approximation. (C) 2001 Optical Society of America.