Estimation of Ice Hydrometeor Types and Shapes from Radar Polarization Measurements

Abstract

An approach to distinguish between various types of ice hydrometeors and to estimate their shapes using radar polarization measurements is discussed. It is shown that elevation angle dependencies of radar depolarization ratios can be used to distinguish between planar crystals, columnar crystals, and aggregates in reasonably homogeneous stratiform clouds. Absolute values of these ratios depend on the reflectivity-weighted mean particle aspect ratio in the polarization plane. Circular depolarization ratios depend on this ratio, and linear depolarization ratios depend on this ratio and particle orientation in the polarization plane. The use of nearly circular elliptical polarization provides a means of measuring depolarization for low reflectivity scatterers when the circular polarization fails due to low signal level in one of the receiving channels. Modeling of radar backscattering was applied to the elliptical depolarization ratios as measured by the Ka-band radar developed at the NOAA Environmental Technology Laboratory. Experimental data taken during the Winter Icing and Storms Instrument Test experiment in 1993 generally confirmed the calculations and demonstrated the applicability of the approach.