WindSat is a satellite-based multi-frequency polarimetric microwave radiometer designed to measure the fully polarimetric radiometric brightness temperature (TB) at 10.7, 18.7, and 37.0 GHz, and linearly polarized TB at 6.8 and 23.8 GHz. The primary goal of WindSat is to demonstrate the capability of polarimetric microwave radiometry in remote sensing of the ocean surface wind vector. Sea surface temperature, water vapor, and cloud liquid water, are among some of the other geophysical parameters that can also be measured. Solution of an inverse method to retrieve these environmental parameters from the polarimetric radiometer measurements requires a forward model that characterizes the measured brightness temperature due to emission from the surface and the intervening atmosphere, and its transmission through the atmosphere.
This paper concentrates predominantly on the atmospheric component of the Windsat forward model. This includes two separate but related algorithms. We have developed a complete radiative transfer model that calculates the upward and downward atmospheric radiation, including attenuation effects due to clear air (both resonant and continuum absorption by water vapor and molecular oxygen) and non-precipitating clouds. From calculations and analysis of using this full forward model and an extensive match-up dataset a computationally efficient one-layer parameterized model has been developed for use in the physically-based Windsat retrieval algorithm. A performance assessment of forward models which utilize surface and atmospheric models, NWP model data assimilation profiles, and environmental measurements from other satellites, by comparison with WindSat measurements, is presented.