A parametrization of vertically-variable horizontal non-uniformity of rain within the GPM-DPR beams

The “non-uniform beam filling” (NUBF) problem has received much attention in the context of retrieving instantaneous rain amounts from radar measurements because of the non-linearity of the relation between the amount of rain and the signature it leaves in the received echo signals. The non-linearities convert additive white uncertainty into biases in the measured quantities, and the accuracy of any estimate of the biases depends on how detailed a description one can use of the underlying non-uniformity. In this paper, we describe a method that we developed to characterize this non-uniformity in a very similar way to the treatment of Hydrometeor-Size-Distribution variability, by parametrizing it. This should be particularly useful to allow retrieval algorithms to account for NUBF in a more realistic way.