Symmetry analysis of DDSCAT-based phase matrix for 3-D microwave RT model development

A horizontally inhomogeneous unified microwave radiative transfer (HI-UMRT) model based on nonspherical hydrometeor scattering is being developed at University of Colorado at Boulder to facilitate the forward radiative simulations of transmittivity and reflectivity over 3-dimensional inhomogeneous clouds in severe weather. The HI-UMRT model provides a 3-D radiative intensity solution by incorporating the planar-stratified UMRT algorithm with a horizontally inhomogeneous iterative perturbation method. The HI-UMRT solution could inherit the properties of computational stability, efficiency and accuracy from the UMRT algorithm as long as the symmetry of discretized phase matrix computed by discrete dipole approximation (DDA) could be identified for large nonspherical hydrometeors. In this study, the required symmetry of discretized phase matrix in the HI-UMRT model was explicitly defined and a new method of calculating the single-scattering full Stokes matrix based upon the DDSCAT software package was developed. A total of 60 snow/ice aggregates of 16 particle types and of particle sizes from 150 to 1,100 μm covering the full spectrum of DDSCAT database were selected for the study. The result showed that the required symmetry conditions are satisfied for all selected particles. It leads to a conclusion with strong confidence that coupled analytical RT solutions for the first two Stokes parameters with inherent matrix stability and high computational efficiency can be achieved in the HI-UMRT model.