GEOMETRIC-OPTICS-INTEGRAL-EQUATION METHOD FOR LIGHT-SCATTERING BY NONSPHERICAL ICE CRYSTALS

A new geometric-optics model has been developed for the calculation of the single-scattering and polarization properties for arbitrarily ori ented hexagonal ice crystals. The model uses the ray-tracing technique to solve the near field on the ice crystal surface, which is then tra nsformed to the far field on the basis of the electromagnetic equivale nce theorem. From comparisons with the results computed by the finite- difference time domain method, we show that the novel geometric-optics method can be applied to the computation of the extinction cross sect ion and single-scattering albedo for ice crystals with size parameters along the minimum dimension as small as similar to 6. Overall agreeme nt has also been obtained for the phase function when size parameters along the minimum dimension are larger than similar to 20. We demonstr ate that the present model converges to the conventional ray-tracing m ethod for large size parameters and produces single-scattering results close to those computed by the finite-difference time domain method f or size parameters along the minimum dimension smaller than similar to 20. The present geometric-optics method can therefore bridge the gap between the conventional ray-tracing and the exact numerical methods t hat are applicable to large and small size parameters, respectively. ( C) 1996 Optical Society of America