A parameterization of the microwave land surface emissivity between 19 and 100 GHz, anchored to satellite-derived estimates

Land surface emissivities have been calculated for Tropical Rainfall Measuring Mission (TRMM) Microwave Instrument (TMI), Special Sensor Microwave/Imager (SSM/I), and Advanced Microwave Sounder Unit-A conditions, for two months (July 2002 and January 2003) over the globe at the European Centre for Medium-Range Weather Forecasts, directly from satellite observations. From this data set, a parameterization of the microwave emissivities that account for frequency, incidence angle, and polarization dependences is proposed. It is anchored to climatological monthly mean maps of the emissivities at 19, 37, and 85 GHz, which are calculated from SSM/I. For each location and time of the year, it provides realistic first-guess estimates of the microwave emissivities from 19 to 100 GHz, for all scanning conditions. The results are compared to radiative transfer model estimates. The new estimates provide rms errors that are usually within 0.02, with the noticeable exception of snow-covered regions where the high spatial and temporal variabilities of the emissivity signatures are difficult to capture.