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/spl times/43 km) and 22.235 GHz (60/spl times/40 km) channels are enhanced to the same spatial resolution as the 37 GHz channels (37/spl times/29 km) using the method by Robinson et al. (1992).

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