Rainfall Estimation Using Polarimetric Techniques at C-Band Frequencies

Abstract

The accuracy of radar measurements and their derived parameters, such as rainfall rate, are compromised by errors caused by propagation effects at C-band frequencies. The radar measurements of reflectivity factor Z and differential reflectivity ZDR are affected by the absolute and differential attenuation through the rain medium. Another useful radar-derived parameter, differential propagation phase shift ΦDP, is contaminated by the differential phase on backscatter δ, which attains significant values in rainfall at C-band frequencies. In this paper we present a technique to correct these propagation and backscatter effects by application of an algorithm that corrects first Z and ZDR, using relationships between the specific and differential attenuations versus phase shift, which is followed by estimation of the differential backscatter phase shift parameter δ from the corrected ZDR. Simulation results are presented to demonstrate the effectiveness of this correction procedure for two cases: (a) uniform rainfall along the path, and (b) rainfall varying with range. We also present estimates of accuracy in the measurement of radar-derived rainfall rates made after applying this correction procedure.