Rainfall estimation by combining radar and infrared satellite data for nowcasting purposes

The aim is to evaluate the use of infrared satellite precipitation estimates for nowcasting purposes in the context of a real-time flood-warning scheme. A radar-based calibration technique is described which is applied to the Negri-Adler-Wetzel scheme. This procedure employs radar data over a defined calibration area to estimate, for each satellite image, actual min-rates to be used in the Negri-Adler-Wetzel scheme. Calibrated satellite estimates obtained from this procedure can be used to diagnose areas of precipitation beyond radar range, thus allowing an extension of precipitation nowcasting lead time. Calibrated estimates are compared with radar rainfall measurements and results are discussed for various sizes of integration area. Calibration reduces consistently both bias and variance of the error of the original Negri-Adler-Wetzel estimates, even for integration areas as small as 2000 km(2). This indicates the capabilities of the new technique for nowcasting purposes over medium-sized river basins.