PRECIPITATION RETRIEVAL FROM SPACEBORNE MICROWAVE RADIOMETERS BASED ON MAXIMUM A-POSTERIORI PROBABILITY ESTIMATION

A retrieval technique for estimating rainfall rate and precipitating c loud parameters from spaceborne multifrequency microwave radiometers i s described. The algorithm is based on the maximum a posteriori probab ility criterion (MAP) applied to a simulated data base of cloud struct ures and related upward brightness temperatures, The cloud data base i s randomly generated by imposing the mean values, the variances, and t he correlations among the hydrometeor contents at each layer of the cl oud vertical structure, derived from the outputs of a time-dependent m icrophysical cloud model, The simulated upward brightness temperatures are computed by applying a plane-parallel radiative transfer scheme, Given a multifrequency brightness temperature measurement, the MAP cri terion is used to select the most probable cloud structure within the cloud-radiation data base, The algorithm is computationally efficient and has been numerically tested and compared against other methods, It s potential to retrieve rainfall over land has been explored by means of Special Sensor Microwave/Imager measurements for a rainfall event o ver Central Italy, The comparison of estimated rain rates with availab le raingauge measurements is also shown.