IMPROVEMENT OF THE DUAL-FREQUENCY PRECIPITATION RETRIEVAL METHOD FOR A GLOBAL ESTIMATION OF THE Z-R RELATIONSHIP

Abstract

The Z-R relationship (Z=aR^b) between radar reflectivity factor Z and precipitation rate R has been used for operational radar measurements, but its coefficients (a, b) are known to be highly variable in time and space and also dependent on precipitation types. The Dual-frequency Precipitation Radar (DPR) is expected to instantaneously estimate the 2-moment drop size distribution (DSD) function and to finally derive global maps of (a, b). For this big goal, it is necessary to improve the accuracy of the instantaneous dual-frequency retrieval method. In this study, Mardiana’s method (MA04) is tested with a simulated DPR measurement dataset, and it is found that MA04 has negative bias which corresponds to 40% of the true precipitation rate. While the true equivalent radar reflectivity factor Z_e does not change largely along the range, the estimates of Z_e by MA04 tend to be smaller at lower range bins. MA04 is modified into three new methods. In the best method, the bias is limited to 18% of the truth.