Statistics of depolarization ratio from an airborne backscatter lidar

An important cloud optical property derived from elastic backscatter lidars is depolarization ratio because it is used to determine cloud phase. Statistics and trends of volume depolarization ratio were analyzed for four years, 2003-2007, of Cloud Physics Lidar data during five projects of varying geographic locations and meteorological seasons. The volume depolarization ratio was computed using the parallel and perpendicular polarized 1064 nm channels. The majority of the cloud layers yielded a volume depolarization ratio between 0.3 and 0.6 with the volume depolarization ratio frequency distribution centered at 0.45 for ice clouds and 0.05 for water clouds. On average for ice clouds, volume depolarization ratio increased significantly as temperatures decreased. No trend for water clouds was observed, since all water particles are in theory spherical.