Predicted effects of nonuniform beam filling on rainfall retrieval for the geostaionary Doppler weather radar

Abstract

A novel instrument concept, Geostaionary Doppler Weather Radar, namely NEXRAD in Space (NIS), is developed for detailed monitoring of hurricanes, cyclones, and severe storms from a geostationary orbit., which has higher time-sampling and wider obversation area than those of low orbit weather radar such as TRMM and DPR radar. However, because of its too far distance away from the surface of the earth, even sharper beam width up to 0.019°, it will lead to more than 12 kilometers horizontal resolution near surface, so that errors of nonuniform beam filling (NUBF) on rainfall retrieval would probably be fatal, especially for small scale convective rainfall. Due to no real data of NIS, an investigation using the high resolution data of the Second Generation Airborne Precipitation Radar (APR-2) to simulate low resolution NIS data is first started in this paper for the estimation of NUBF errors similar to the works before TRMM and DPR launched. Algorithms of rainfall retrieval and path-integrated attenuation(PIA) under uniform and nonunifrom beam filling are introduced to estimate these errors, and a statistic method is used to evaluate the error numerical distrubtion. Remakable results show that the errors due to NUBF are prospectively serious and the biases of PIA and reflectivity in the bottom of rainfall are larger and would lead to the rainfal retrieval to be overestimated or underestimated, their maximum biases could be larger than 15dB under small scale convective rainfall system. © 2012 Springer-Verlag GmbH.