Nonuniform beamfilling correction for spaceborne radar rainfall measurement: Implications from TOGA COARE radar data analysis

A method is studied to make a nonuniform beamfilling (NUBF) correction for the path-integrated attenuation (PIA) derived from spaceborne radar measure ment. The key of this method is to estimate rain-rate variability within a radar field of view from the local statistics of a radar-measurable quantit y ([Q]) such as PIA derived from the surface reference technique. Statistic al analyses are made on spatial variabilities of the radar-measurable quant ities using a shipborne radar dataset over the tropical Pacific obtained du ring the TOGA COARE field campaign. It is found that there are reasonably g ood correlations between the coarse-scale variability of [Q] and the finesc ale variability of rain rate, and the regression coefficient (slope) of the se two quantities depends somewhat upon rain types. Based on the statistica l analyses, the method is tested with a simulation using the same dataset. The test result indicates that this method is effective in reducing bias er rors in the estimation of rain-rate statistics. Although it is also effecti ve to make the NUBF correction on an individual instantaneous field-of-view basis, one must account for the variability of local rainfall statistical characteristics that may cause significant errors in the NUBF correction.