Melting layer detection validation from GPM DPR and dual-polarization ground radar

The Global Precipitation Measurement (GPM) mission was successfully launched in February 2014. The GPM core satellite is equipped with a dual-frequency precipitation radar (DPR) operating at Ku- (13.6 GHz) and Ka- (35.5 GHz) band. DPR on aboard the GPM core satellite is expected to improve our knowledge of precipitation processes relative to the single-frequency (Ku- band) radar used in TRMM (Tropical Rainfall Measurement Mission) by providing greater dynamic range, more detailed information on microphysics, and better accuracies in rainfall and liquid water content retrievals. New Ka- band channel observation of DPR helps to improve the detection thresholds for light rain and snow relative to TRMM PR [1]. The dual-frequency signals allow us to distinguish regions of liquid, frozen, and mixed-phase precipitation.

Profile classification module of GPM-DPR involves two main aspects: 1) precipitation type classification, including classifying stratiform, convective, and other rain type; and 2) melting region detection [2][3]. Dual-frequency classification method that has been implemented into GPM-DPR algorithm relies on the microphysical properties using the difference in measured radar reflectivities at the two frequencies, a quantity often called the measured dual-frequency ratio (or DFRm).

Ground validation is an integral part of all satellite precipitation missions. Ground validation helps to characterize errors, quantify measurement uncertainty, and, most importantly, provides insight into the physical basis of the algorithms. Dual polarization NEXRAD radar is used to perform ground validation of melting layer with DPR in this study. Overlaps between DPR radar and NEXRAD radar are carefully selected. Hydrometeor classification [4] is performed for NEXRAD radar and cross compared with classification results from DPR. Good agreements can be found in the comparison.