Small-scale nonuniform rain beam filling errors in spaceborne radar rain measurement

Abstract

An observational method has been proposed to sample echo data with high range resolutions using a ground-based meteorological radar. Utilizing this method, a quantity of rain echo data with a high range resolution of 125 m was obtained by using an X-band meteorological radar. The computation of rain nonuniformity strength using this high resolution radar data shows that the nonuniformity is significant and even in an instantaneous field of view (IFOV) of 1 km, the reflectivity excursion above 10 dB is common. The simulation of the nonuniform beam filling (NUBF) error of the path-averaged rainrate derived from the path-integrated attenuation measured by the spaceborne radar has been also implemented using this data. The results show that the rainrate encounters mainly underestimation and cannot be neglected, even in 0.5 km IFOV, it can reach over 50%. The correlation analyses show that the rainrate error and the true rainrate have a power relationship with some correlation, which might be used to correct this error partially. The simulation also shows that it is very important to use the high resolution data in studying the NUBF error of the next generation spaceborne radar with a higher across beam resolution (e.g. below 3 km).