Doppler Polarimetric Radar Measurements of the Gamma Drop Size Distribution of Rain

Abstract

The conversion of radar reflections into rain intensities is dependent upon assumptions regarding the drop size distribution. The gamma drop size distribution contains three unknown parameters; the number of parameters that can be obtained depends on the number of radar observables. When only the reflectivity is measured, one parameter is derived, combining it with the differential reflectivity results in the retrieval of two parameters, and when Doppler measurements are done as well, a third parameter is obtained. The Doppler spectrum may be distorted by turbulence; a correction procedure is developed. The combination of copolar and cross-polar radar measurements is used to estimate the canting-angle distribution. Analysis of data of the Delft atmospheric research radar during a moderate event shows that the three parameters of the gamma drop size distribution are statistically related. Combining these relationships results in an event-specific Z-R relationship.