ISEM-6: Infrared Surface Emissivity Model for RTTOV-6
SHERLOCK, Vanessa
The default infrared surface emissivity model has been revised for the Version 6 release of the NWP fast radiative transfer operator RTTOV. Previously a unit emissivity default, independent of surface type, has been assumed in the infrared. In ISEM-6, the Infrared Surface Emissivity Model for RTTOV-6, default surface emissivity models are implemented for different surface types (sea/land/snow/?sea-?ice). The Masuda sea surface emissivity model at zero windspeed has been adopted as the default infrared surface emissivity model over sea, based on results of studies appearing in the literature. The assumptions of a windspeed independent emissivity and specular reflection lead to an underestimation?, albeit small, of the upwelling longwave radiation; brightness temperature errors are less than 0.15 K in all but the driest atmospheres at high windspeeds. The satellite zenith angle dependence of the rough sea surface channel average emissivity has been parameterised for all infrared channels on the NOAA 2-15 (VTPR, HIRS and AVHRR), GOES 8-12, METEOSAT 5-7 and MSG 1 satellites. Pre-operational trial results indicate that the new sea surface emissivity parameterisatio?n should significantly reduce latitudinal and scan angle dependent bias corrections. Uncertainties still remain surrounding the validity of the Cox and Munk slope variance statistics at high windspeed and the emissivity of foam in the infrared. Further ...
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