Validation of Precipitation Measurements From the Dual-Frequency Precipitation Radar Onboard the GPM Core Observatory Using a Polarimetric Radar in South China

The dual-frequency precipitation radar (DPR) onboard the global precipitation measurement (GPM) satellite provides valuable measurements of precipitation. In this study, the GPM DPR products (version 6) are validated against a ground-based S-band polarimetric radar in South China based on a volume-matching method. Good consistency is found for the reflectivity factor (
$Z$
) calibration of the two instruments. From the perspective of microphysics, the mass-weighted mean diameter (
$D_{m}$
) estimates correspond well with those of the ground-based radar in the inner swath of the normal scan (NS); however, underestimation is found for the raindrop number concentration, indicated by the generalized intercept parameter (
$N_{w}$
), especially for the intense echoes. Thus, the GPM DPR product may fail to depict the microphysical characteristics of small-to-medium raindrops in high concentration for heavy rainfall in South China. This is attributed to the negative
$Z$
bias of the DPR caused probably by insufficient correction of attenuation, which also leads to clear underestimation in the liquid water content (
$W$
) and the rainfall rate (
$R$
) products for intense echoes. In the outer swath where only single-frequency retrieval is available, overestimation in
$D_{m}$
exists regardless of echo intensity level, and more underestimation can be found in
$N_{w}$
,
$W$
, and
$R$
especially for intense echoes. In the selected typhoon and squall line cases, better capability in revealing microphysical properties is also found for the inner swath of the NS. After adjusting the scan mode, the performance of the precipitation products in the outer swath can be improved by dual-frequency retrievals in the future.