Computation of electromagnetic characteristics of frozen hydrometeors at millimeter-wave frequencies

The development of physical model to retrieve snowfall from millimeter-wave measurements require the calculation of scattering and emission properties which can generate brightness temperatures (Tbs) and/or radar reflectivities that are consistent with observations. Frozen hydrometeors have various sizes, shapes, orientations, phase, and density so that it is difficult to parameterize their electromagnetic (EM) properties. For many physical approaches in remote sensing, non-spherical frozen hydrometeors are parameterized as spherical particles and Mie-theory is employed because it is faster than more rigorous analyses of scattering by nonspherical particles. However, the applicability of those simplified approximations in millimeter-wave radar and radiometer remote sensing of frozen hydrometeors has not yet been proved. To seek a parameterization to represent the EM properties of frozen hydrometeors at millimeter-wave frequencies, this study employs the Discrete Dipole Approximation (DDA) method Drain and Flatau (2003) and analyzes the calculated single scattering from nonspherical snow crystals at millimeter-wave frequencies (95, 140, 183, 220, and 340 GHz). Various assumptions, which were made in previous studies, for the snow microphysical properties, such as density, dimension, and particle size distribution are applied to these comparisons. The uncertainty range of EM property caused by various snow habits, density, and particle size distribution are presented