Optical properties of a dispersion of anisotropic particles with non-randomly distributed orientations. The case of atmospheric ice crystals.

The orientational distribution of the particles in a dispersion plays an important role in determining the optical properties of the dispersion as a whole. Since assessing the reliability of an assumed orientational distribution requires calculating an ensemble average over the particles concerned, we examine a few cases of orientationaldistributionsthatallowforanalyticalcalculationoftheaverageintheframeworkofthe transition matrix approach. Explicit formulas are given and applied to the calculation of the forward- scattered and backscattered intensity from dispersions of model particles meant to simulate the optical behavior in the infrared of the atmospheric ice crystals that occur as hexagonal platelets.