Intercomparison of Attenuation Correction Methods for the GPM Dual-Frequency Precipitation Radar

A new attenuation correction method has been developed for the dual-frequency precipitation radar (DPR) on the core satellite of the Global Precipitation Measurement (GPM) mission. The new method is based on Hitschfeld and Bordan's attenuation correction method (HB method), but the relationship between the specific attenuation k and the effective radar reflectivity factor Z(e) (k-Z(e) relationship) is modified by using the dual-frequency ratio (DFR) of Z(e) and the surface reference technique (SRT). Therefore, the new method is called the HB-DFR-SRT method (H-D-S method). The previous attenuation correction method, called the HB-DFR method (H-D method), results in an underestimation of precipitation rates for heavy precipitation, but the H-D-S method mitigates the negative bias by means of the SRT. When only a single-frequency measurement is available, the H-D-S method is identical to the HB-SRT method (H-S method). The attenuation correction methods were tested with a simple synthetic DPR dataset. As long as the SRT gives perfect estimates of path-integrated attenuation and the adjustment factor of the k-Z(e) relationship (denoted by epsilon) is vertically constant, the H-S method is much better than the dual-frequency methods. Tests with SRT error and vertical variation in epsilon showed that the H-D method was better than the H-S method for weak precipitation, whereas the H-S method was better than the H-D method for heavy precipitation. The H-D-S method did not produce the best results for both weak and heavy precipitation, but the results are stable. Quantitative evaluation should be done with real DPR measurement datasets.