Estimation of Specific Differential Phase and Differential Backscatter Phase From Polarimetric Weather Radar Measurements of Rain

The estimation of the specific differential phase particularly in the presence of the differential backscatter phase and nonuniform propagation paths is a long-standing goal in weather radar polarimetry. Furthermore, a reliable estimator of the differential backscatter phase for precipitation measurements has not been proposed yet, although it contains valuable information about the presence of non-Rayleigh scattering and the microphysics of precipitation. In this letter, we introduce a novel method to estimate the specific differential phase and the differential backscatter phase from polarimetric weather radar measurements of rain. This estimation does pay off particularly at the X-band where the scattering regime is non-Rayleigh already in moderate rain. In this case, the differential backscatter phase is useful as an additional weather radar observable with manifold applications such as rain rate estimation, microphysical retrieval, and operational radar calibration. The novel method also provides an improved range resolution of the specific differential phase compared to conventional estimators. We illustrate the estimation of the differential phases with data from the Delft University of Technology's polarimetric X-band International Research Centre for Telecommunications and Radar drizzle radar.