SEPARATION OF PROPAGATION AND BACKSCATTERING EFFECTS IN RAIN FOR CIRCULAR-POLARIZATION DIVERSITY S-BAND RADARS

Because precipitation particles are generally nonspherical, not only w ill microwave radiation be depolarized when reflected by precipitation , but also the polarization state of the transmitted wave will change as the radar beam penetrates the region of precipitation. The intrinsi c scattering properties of the hydrometeors are, therefore, coupled wi th the properties of the propagation medium, and both effects contribu te to establish the return signal. In this paper it is shown that thes e effects can be separated when S-band circular polarized radiation is transmitted and the copolar and cross-polar power. and the magnitude and phase of the copolar and cross-polar signal correlation, is availa ble. The equations of the radar observables for a model medium contain ing nonspherical raindrops are presented. This model takes into accoun t the distribution of canting angle but assumes the uniformity of the distribution function along the propagation path. Assuming the raindro ps to have the same orientations throughout the region of precipitatio n and using two empirical relationships relating the mean and the diff erential attenuation to the differential phase shift, a set of equatio ns for separation of propagation and backscattering effects is develop ed. Application of this to a model convective cell verifies that the u se of the circular polarization technique at S band can also provide v ery good estimates of the intrinsic scattering properties of precipita tion in regions of heavy rain rates. Data from a circularly polarized S-band radar system are used to confirm that this separation may be pe rformed and to illustrate the microphysical information that can now h e extracted.