Rain Rate Estimates from Differential Polarization Measurements

Abstract

This paper presents an analysis of the accuracy of rain rate estimates from data observed with a radar that has alternating horizontal and vertical polarization. Theoretical accuracies of rain rates from the reflectivity, the differential reflectivity and the differential propagation phase shift are considered via-a-vis the drop size distribution (DSD) variability, using a computer simulation procedure. First measurements of the differential propagation phase shift have been provided by the National Severe Storms Laboratory's dual-polarized radar, in addition to the reflectivity and the differential reflectivity. An examination of the radar data has revealed factors that could affect the rain rate estimates to a greater extent than the often contended DSD variability in the case of differential reflectivity method. Errors caused by sidelobe contamination significantly affect the differential phase shift data, so that a large spatial scale averaging is required to obtain reasonably accurate rain rate estimates, thus limiting the spatial resolution possible.