Using CloudSat to Assess the Impacts of Sensitivity and Spatial Resolution on Precipitation Retrievals from Future Space-borne Multi-Frequency Radar Missions

Identifying and quantifying near-surface precipitation rates from space-borne radar platforms involves many unique challenges relative to surface-based instrumentation. The significance of partial beam filling, undetected precipitation, and ground clutter depend strongly on the choice of satellite altitude, pulse length, antenna size, transmit power, and on-orbit signal processing. Given the ongoing efforts to development new space borne multi-frequency radar concepts, a critical observation-based analysis of the tradeoffs associated with various sensor choices is overdue. The W-band Cloud Profiling Radar (CPR) aboard the CloudSat offers a unique dataset for such a sensitivity analysis, given its high horizontal resolution and low minimum detectable signal for precipitation identification. Here, CPR observations spanning the years 2007 to 2010 are modified to quantify tradeoffs related to choices of instrument sensitivity and field of view for future satellite-based multi-frequency precipitation radars. Specifically, the impacts of degrading spatial resolution from 1.1 km to 5.5 km and varying radar sensitivity from -15 through 10 dBZ on precipitation detection and intensity estimation will be assessed as a function of geographic location, convective/stratiform precipitation type, and precipitation phase. Results demonstrate that while the retrieved probability of precipitation (PoP) increases steadily as effective field of view is increased as expected, partial beam filling effects cause substantial deviations from the predicted scaling relationship as radar sensitivity is decreased. Furthermore, it will be demonstrated that reduced spatial resolution can significantly bias precipitation intensity estimates in non-trivial ways. These effects are found to be particularly significant in regions characterized by frequent isolated, light precipitation and in frozen precipitation.