Precipitation measurements using 183-GHz AMSU satellite observations

The 183-GHz humidity channels of the Advanced Microwave Sounding Unit (AMSU) on the NOAA-15 operational weather satellite respond in part to precipitation. The 15-km resolution data at 183.31/spl plusmn/7 and 183.31/spl plusmn/1 GHz were combined to yield point precipitation estimates from a simple neural network trained using NEXRAD radar precipitation data. A computer used these estimates to locate all significant precipitation cells and to define extended nonoverlapping geographic regions centered on each. The total estimated precipitation rates (liters/sec) and areas for these regions were then fed to a second neural network trained using NEXRAD data. One two-day test involved the eastern United States during a major frontal passage and a major hurricane. NEXRAD missed regions where 2.3 percent of the AMSU-NEXRAD-estimated rain fell, and AMSU missed regions where 11.8 percent of the NEXRAD-estimated rain fell. For those 18 test regions detected by both systems, the precipitation-weighted rms difference between AMSU- and NEXRAD-based cell-wide precipitation estimates was 2.2 dB; these 18 test regions were different from the 18 used to train the second network. Percentage differences in precipitation were generally smaller for the larger rain cells.