Evidence of multiple scattering in observations of the GPM dual-frequency precipitation radar and way forward for retrievals

This paper illustrates how multiple scattering signatures affect Global Precipitation Measuring Mission Dual-Frequency Precipitation Radar (DPR) Ku and Ka band reflectivity measurements, and how they are consistent with pre-launch assessments based on theoretical considerations and confirmed by airborne observations. In particular, in presence of deep convection, certain characteristics of the dual wavelength reflectivity profiles cannot be explained with single scattering whereas they are readily explained by multiple scattering theory. Examples of such signatures are the absence of surface reflectivity peaks, anomalously small reflectivity slopes in the lower troposphere and anomalous behavior of the signal at ranges longer than that corresponding to the surface. These signatures will be demonstrated for a variety of cases occurred over the Continental US. A path to refining the rainfall inversion problem is proposed by adopting a methodology based on a forward operator which accounts for multiple scattering. A retrieval algorithm based on this methodology is applied to a variety of case studies with collocated NEXRAD observations available. This allows rigorously assessing the actual profiling capability of the DPR inside such systems. These findings are relevant for DPR-based rainfall retrievals and stratiform/convective classification algorithms when dealing with deep convective regions.