Light scattering by hexagonal ice crystals: comparison of finitedifference time domain and geometric optics models
Abstract
We have developed a finitedifference time domain (FDTD) method and a novel geometric raytracing model for the calculation of light scattering by hexagonal ice crystals. In the FDTD method we use a staggered Cartesian grid with the implementation of an efficient absorbing boundary condition for the truncation of the computation domain. We introduce the MaxwellGarnett rule to compute the mean values of the dielectric constant at grid points to reduce the inaccuracy produced by the staircasing approximation. The phase matrix elements and the scattering efficiencies for the scattering of visible light by twodimensional long circular ice cylinders match closely those computed from the exact solution for size parameters as large as 60, with maximum differences less than 5%. In the new raytracing model we invoke the principle of geometric optics to evaluate the reflection and the refraction of localized waves, from which the electric and magnetic fields at the particle surface (near field) can be computed. Based on the equivalence theorem, the near field can subsequently be transformed to the far field, in which the phase interferences are fully accounted for. The phase functions and the scattering efficiencies for hexagonal ice crystals computed from the new geometric raytracing method compare reasonably well with the FDTD results for size parameters larger than approximately 20. When absorption is involved in geometric ray tracing,
 Publication:

Journal of the Optical Society of America A
 Pub Date:
 January 1995
 DOI:
 10.1364/JOSAA.12.000162
 Bibcode:
 1995JOSAA..12..162Y
 Keywords:

 SCATTERING;
 WATER;
 CRYSTALS;
 GEOMETRICAL OPTICS;
 TIMEDOMAIN ANALYSIS