Microwave backscattering by nonspherical ice particles at 5.6 GHz using second-order perturbation series

Scattering of microwaves by an ensemble of nonspherical ice particles is studied using a scattering model based on a second-order perturbation series at 5.6 GHz (C-band). Particle shapes are defined using a Gaussian random sphere geometry. Particle inhomogeneity is taken into account using three different effective-medium approximations: Maxwell–Garnett, Bruggeman, and Coherent Potential mixing rules. By systematically varying particle size, liquid water content, Gaussian shape parameters, and internal structure, it is found that liquid water content is the most important factor for the co-polarized backscattering; the shape is relatively unimportant. For depolarized backscattering, the shape is of fundamental importance, although the other factors are significant too. Surprisingly, the type of nonsphericity is found to be important for depolarization even for scatterers that are in the Rayleigh region: elongated targets depolarize clearly stronger than more irregular shapes. This finding seems not to be strongly size dependent, at least for size parameters from 0.0059 to 0.47, and indicates that the accurate modeling of shape is important for polarization quantities even in the Rayleigh region.