Determination of rainfall over the ocean from SSM/I measurements using a library approach

An algorithm is developed to estimate rainfall over the oceans from the passive microwave radiometer SSM/I (Special Sensor Microwave/Imager) on the DMSP (Defense Meteorological Satellite Program) satellites. The method is based on minimizing the difference between the satellite measured brightness temperatures and a large number of simulated brightness temperatures stored in a microwave radiation library (MRL). The MRL is searched for a set of simulated brightness temperatures which coincide with the measured brightness temperatures within predefined error margin. From this set the retrieved parameter value is computed by a simple interpolation technique applied to the corresponding geophysical parameter. A comparison of the authors´ algorithm with two published algorithms has been carried out. Zonally averaged monthly rain rates calculated from the three algorithms show similar structures but different quantities. Another comparison is done for a modified SSM/I data set, for which the spatial resolution of the 19.35 GHz (69×43 km) and 22.235 GHz (60×40 km) channels are enhanced to the same spatial resolution as the 37 GHz channels (37×29 km) using the method by Robinson et al. (1992)