VARIATIONAL INVERSION OF THE SSM I OBSERVATIONS DURING THE ASTEX CAMPAIGN/

Given the prospect of direct assimilation of satellite microwave radia nces within numerical weather prediction (NWP) schemes, this study pro poses to test a nonlinear inversion for retrieving geophysical paramet ers from Special Sensor Microwave/Imager (SSM/I) measurements using NW P forecasts as a priori information. The inversion method relies upon an accurate analysis of the radiative transfer and simultaneously retr ieves the surface wind speed, the integrated water vapor, and the clou d liquid water. The method is rested in the framework of the well-docu mented Atlantic Stratocumulus Transition Experiment campaign. The vali dation approach involves radiosondes from islands, ships, and drifting buoys, cloud liquid water measurements from instruments onboard the U .K. Meteorological Office C-130 aircraft, and the International Satell ite Cloud Climatology Project cloud liquid water estimates. The retrie ved geophysical parameters are in satisfactory agreement with the avai lable in situ measurements, and the inversion process is shown to be r eliable even in the detection of low liquid water contents. The SSM/I inversion scheme is also a strategy for the validation of radiative tr ansfer models, the discrepancy between the simulated and the observed radiances at the end of the inversion process being a powerful tool fo r testing the radiative transfer in use.