Experimental determination of the multiple-scattering effect on the lidar-signal polarization characteristics during liquid- and solid-phase precipitation

We present results of experimental investigations of the signal-polarizatio n characteristics in the case of lidar sounding during precipitation. We sh ow and discuss the lidar signals and the depolarization profiles along the sounding path for liquid- and solid-phase precipitation. In the former case we compare the signal characteristics at different degrees of precipitatio n rate. In the latter situation, we consider snowfall with particle shape c lose to that of Chebyshev particles. We also follow the lidar-signal change s depending on the field-of-view of the receiving optics. The experimental data are compared with results of theoretical estimates and models concerni ng the optical and microphysical characteristics of the rain and snow parti cles. In the case of liquid-phase precipitation - rain - the observed depen dence of the lidar's signal-polarization structure on the precipitation int ensity has two aspects: on the one hand, the change of the raindrops' shape , and, on the other, the multiple-scattering effects. The lidar data demons trate that the signal depolarization, and, more specifically, its behavior along the sounding path, can be used as a criterion for the presence of mul tiple scattering. In the case of a snowfall consisting of Chebyshev particl es, the simultaneous role is evident of two factors influencing the lidar-s ignal depolarization, namely, the non-spherical shape of the particles and the multiple -scattering effects. When the scattering takes place off parti cles with a large size and a shape strongly differing from spherical, we ob served the predominant role of the non-sphericity of the scattering centers in the signal depolarization.