Retrieval of Attenuation Profiles from the GPM Dual-frequency Radar Observations

A new method that retrieves attenuation profiles using a Dual-frequency Precipitation Radar (DPR) equipped on the Global Precipitation Mission (GPM) is proposed. The DPR operates at Ka and Ku-bands and provides profiles of a differential frequency ratio, which is the difference of the measured or attenuated reflectivity in decibel scale between Ka and Ku bands. For accurate measurements of precipitation, hydrometeor classification is essential. Attenuation of radio wave due to precipitation is closely related to microphysical properties and available for hydrometeor classification. The proposed method estimates range variations of relative values of differential attenuation between two frequencies and can be used for identifying hydrometeor types along the radar propagation path. Numerical simulations indicate that the proposed method performs well for rain, melted snow, mixed-phase precipitation, and some cases of the melting layer. The method was also evaluated for GPM DPR measurements. Results indicate that the method works well for identifying rain and snow and also provides useful information for melting layer detection and attenuation, even for the melting layer in which no enhancement of reflectivity is observed.