Error structure of radar rainfall measurement at C-band frequencies with dual polarization algorithm for attenuation correction

A simple procedure is developed to estimate specific attenuation and differential attenuation at C-band frequencies from the dual polarization radar measurements, reflectivity at horizontal polarization (Z(H)), and differential reflectivity (Z(DR)). An algorithm is presented to correct C-band reflectivity and differential reflectivity measurements for absolute attenuation and differential attenuation, respectively. The effect of the attenuation correction procedure on the error structure of rainfall estimation is studied by utilizing data collected by the dual polarized C-band radar, POLAR 55C, as well as a network of rain gages over the Arno River basin near Florence, Italy. Radar rainfall estimates are compared over two small basins, one close to the radar, at a distance of 35 km, and the other farther from the radar, at a distance of 65 km, where the effect of attenuation is likely to be more significant. On the basis of a comparative study of radar and rain gage measurements over the two basins it is shown that the attenuation correction improves the radar rainfall estimates based on Z - R algorithms for both basins. The correction procedure improves the radar rainfall estimates based on dual polarization algorithm for the farther basin; however, the attenuation correction does not improve the radar rainfall estimates based on dual polarization algorithm for the closer basin (when the differential attenuation is not significant).