Rainfall estimation by S-band polarimetric radar in Korea. Part I: preprocessing and preliminary results

The empirical relationships used to estimate rainfall amounts from polarimetric radar observations were developed and tested by using long-period drop size distribution (DSD) data and monitoring of rainfall events prior to operational use in Korea. Rainfall associated with Typhoon Meari in 2011 was selected to assess the performance of these relationships for point and areal rainfall amounts. Data quality was checked in regions of light rain to enable the quantitative use of polarimetric variables. The distributions of the cross-correlation co-efficient and standard deviation of the differential phase shift agreed with those established in a previous study, but the absolute average deviation of differential reflectivity (Z(DR)) was a little distorted. Biases in reflectivity (Z) and differential reflectivity were calculated following established methods and found to be -0.18 and 0.47 dB, respectively. The accuracy of rainfall amounts calculated from R(K-DP) and R(K-DP, Z(DR)) was poor. The best estimates of rainfall were obtained using R(Z, Z(DR)) based on DSDs from Oklahoma (OKC) in the USA and Busan (BSC) for both the point and areal mean cases. Correlation co-efficients of R(Z, Z(DR)) using the BSC DSDs were better than those using the OKC DSDs for areal mean rainfall amounts. Rainfall amounts in this particular case in Korea were estimated more accurately using the Brandes drop shape for R(Z, Z(DR)) than the equilibrium drop shape.