The Application of Multi-Parameter Radar in GPM Ground Validation

Global Precipitation Measurement Mission (GPM) precipitation retrieval algorithms require quantitative multi-scale descriptions of naturally-occurring liquid and frozen precipitation and its spatial variability. Here, ground-based polarimetric and multi-frequency radars serve the basic function of bridging relative point observations of precipitation provided by instruments such as rain gauges and disdrometers to expanded domains that reach into the vertical column and across scales and regions more appropriate to the fields of view associated with satellite remote sensing. Alternatively, NASA Airborne radars serve as satellite simulators, sampling from a similar downward-looking vantage point and using frequencies similar to that flown on the GPM Core satellite. Of particular interest are distributed polarimetric and/or multi-frequency radar observations that can be used to quantify the intrinsic characteristics of precipitation such as gamma drop size distribution parameters (e.g., R, Zku, Zka, Nw, mu, Dm), hydrometeor phase (e.g., rain, snow, mix), water contents, precipitation rate, and precipitation class (convective/stratiform). These observations are often collected at high space/time resolution in both the horizontal (PPI) and vertical (RHI) dimensions. Observation of these parameters can be tied to a description of the precipitation process, multi-dimensional coupling of that process to spatial variability along and across individual to multiple GPM instrument rays/pixels. Thus in addition to providing an appropriate source for direct validation of GPM products, GV radar datasets can be applied to GPM radar retrieval algorithm challenges such as identification of hydrometeor phase, path integrated attenuation, and non-uniform beam filling- all of which can significantly impact estimation uncertainties in precipitation rate. In this study we summarize the use of multi-parameter ground and airborne radars in GPM field measurements for different meteorological regimes. Select results will be presented, ranging in scale from individual case approaches to continental scale radar applications in GPM validation.