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In this paper an algorithm for retrieving precipitation from Special Sensor Microwave/Imager (SSM/I) satellite microwave data is presented for rainfall occurring over both ocean and land. This algorithm is basically derived from the results of a microwave radiative transfer model of plane‐parallel rain clouds and combines the emission and scattering regimes. The features of the algorithm are as follows: (1) a linear function of horizontally polarized brightness temperature at both 19.35 and 85.5 GHz is used as a parameter to relate rainfall rate, which shows no saturation for rainfall rates up to 50 mm/h; (2) the relationship between the linear function and the rainfall rate is closer to linearity than the relationship between brightness temperature of a single channel and rainfall rate, and therefore the beam‐filling problem is less serious than for single‐channel algorithms; (3) the algorithm includes a correction to a beam‐filing problem that was made on the basis of observational evidence; (4) the threshold for precipitation is derived from the SSM/I data themselves, which includes climatological information; and (5) the algorithm is less sensitive to freezing level height and surface temperature than emission‐based algorithms. Validation of the algorithm is made using surface radar and rain gauge data. The validation shows that rainfall retrievals over ocean are in a satisfactory agreement with the surface observations. Over land, heavy rainfall rate can be detected although the disagreement is significant.
Liu et al. (Sat,) studied this question.