ESTIMATION OF ICE HYDROMETEOR TYPES AND SHAPES FROM RADAR POLARIZATION MEASUREMENTS

An approach to distinguish between various types of ice hydrometeors a nd to estimate their shapes using radar polarization measurements is d iscussed. It is shown that elevation angle dependencies of radar depol arization ratios can be used to distinguish between planar crystals, c olumnar crystals, and aggregates in reasonably homogeneous stratiform clouds. Absolute values of these ratios depend on the reflectivity-wei ghted mean particle aspect ratio in the polarization plane. Circular d epolarization ratios depend on this ratio, and linear depolarization r atios depend on this ratio and particle orientation in the polarizatio n plane. The use of nearly circular elliptical polarization provides a means of measuring depolarization for low reflectivity scatterers whe n the circular polarization fails due to low signal level in one of th e receiving channels. Modeling of radar backscattering was applied to the elliptical depolarization ratios as measured by the K-a-band radar developed at the NOAA Environmental Technology Laboratory. Experiment al data taken during the Winter Icing and Storms Instrument Test exper iment in 1993 generally confirmed the calculations and demonstrated th e applicability of the approach.