Alternate Transmission of +45° and −45° Slant Polarization and Simultaneous Reception of Vertical and Horizontal Polarization for Precipitation Measurement

Abstract

A polarimetric weather radar with alternate transmission of slant linear +45° and ?45° polarization and simultaneous reception of both linear vertical and linear horizontal polarization is considered. The equations of the radar observables for a model medium containing nonspherical hydrometeors are presented. Assuming the hydrometeors to be axially symmetric with a canting angle distribution symmetric about the mean canting angle, a set of equations for separation of propagation and backscattering effects is developed. The mean apparent canting angle, the degree of common orientation of the hydrometeors, and the differential phase shift are obtained. Using empirical relationships, the mean and differential attenuations are estimated by means of the differential phase shift. The intrinsic value of the reflectivity, the differential reflectivity, and the copolar correlation coefficient at zero lag time are then determined. Application of this to a model convective rain cell shows that the use of simultaneous transmission and reception of linear vertical and linear horizontal polarization at S, C, and X bands provides accurate estimates of the intrinsic scattering properties of precipitation. The analysis of the bias on the radar observables due to the assumption of a medium of equioriented hydrometeors shows that all the observables with the exception of reflectivity can be severely affected.