Rain Observations by a Multifrequency Dual-Polarized Radiometer

During the Convective and Orographically Induced Precipitation Study, advanced microwave radiometer for rain identification has continuously acquired measurements at the Atmospheric Radiation Measurement Mobile Facility in the Black Forest from the beginning of August until December 2007. The radiometer has six channels measuring in horizontal and vertical polarizations at 10.65, 21.0, and 36.5 GHz. Rainy events have been selected out of the entire database according to collocated gauges and, subsequently, analyzed. Measured brightness temperatures and (vertical-horizontal) polarization differences are interpreted by comparing with radiative transfer simulations, which account for the presence of nonspherical particles in preferential orientation. Measurements confirm the importance of the polarization signal for separating the effect introduced by non-Rayleigh scatterers and, therefore, the rain from the cloud component. More quantitative interpretation of the signal requires a better understanding of the role played by melting particles and an identification of the 3-D structure of the precipitating system under observation. Both aspects will be tackled in the near future by exploiting the synergy with a coinstalled micro rain radar.