Validate FASTEM Model by Using Well-Calibrated ATMS Observations

Microwave ocean surface emissivity model is very important for satellite data assimilation in NWP model, and it is also often being used as tool to assess the satellite observation bias.  FASTEM is the ocean surface emissivity model being used in RTTOV and CRTM, which are the most popular radiative transfer models being used in satellite data assimilation.  During the years the FASTEM model has been developed through different versions, but model validation is very difficult and model accuracy is not widely discussed due to lack of ground truth. ATMS is a well-calibrated microwave sounding instruments onboard SNPP satellite, its calibration error and correction methods have being widely discussed and well documented, and is being recommended as reference microwave instrument by GSICS community. In this paper, based on the well-calibrated ATMS observations, a polarized error model was established to validate different version of FASTEM models. The study results can be used as reference for NWP community to select optimum ocean surface emissivity model for use in data assimilation.