VERIFICATION OF A SCATTERING-BASED ALGORITHM FOR ESTIMATING RAINFALL OVER THE OPEN-OCEAN

An algorithm for estimating rainfall (based upon scattering of upwelli ng radiation at 85 GHz) using the Special Sensor Microwave Imager (SSM /I) 85 GHz sensor data has recently been developed at the National Oce anographic and Atmospheric Administration's Office of Research and App lications (NOAA ORA). Spatial and temporal variability in the differen ces between simple areal-averaged rainfall estimates from a raingage a nd satellite-derived estimates are examined. These initial comparisons provide insight into the nature of the differences, however, due to s ubstantial amounts of spatial sampling error in the raingage spatial a verages, this approach is ineffective at identifying statistically sig nificant differences. Thus, rainfall estimates for this algorithm are examined over the tropical Pacific using a statistical technique, call ed the ''noncontiguous raingage method'' (NCR), which minimizes spatia l sampling error so that the statistical significance of relationships may be determined. The results indicate that, adjusted with calibrati on coefficients, the ORA algorithm could produce unbiased estimates of areal rainfall for the tropical Pacific region examined in this study .