Depolarization ratios of single ice particles assuming finite circular cylinders

Results of the depolarization ratio (6) of single ice particles in fixed orientations are presented to determine whether discrimination between nonspherical ice crystals (causing depolarization) and spherical water droplets (inducing no depolarization) can be made. A T-matrix method is used to compute 6 over a range of particle diameters from 0.13 to 4 mu m and aspect ratios chi = d/h (d is the diameter and h the height of the particle) from 0.3 to 3, where ice crystals are assumed to have a circular cylindrical shape. The depolarization ratio is primarily dependent on the orientation of the particle. Some orientations return no depolarization, whereas others generate values reaching almost delta = 1. Considering the depolarization averaged over all orientations, a dependence of 8 with the particle size is observed where values close to 0.25 are reached. No strong influence of the aspect ratio on the depolarization for a given particle size of 2 mu m is evident, as values remain in a range between 0.2 and 0.3. (C) 2007 Optical Society of America.