A Comparison of Microwave Window Channel Retrieved and Forward-Modeled Emissivities over the US Southern Great Plains

An accurate understanding of land surface emissivity in terms of associated surface properties is necessary for improved passive microwave remote sensing of the atmosphere, including water vapor, clouds, and precipitation, over land. In an effort to advance this understanding, emissivities are calculated for a 5-degree region in the US Southern Great Plains using a combination land surface model and physical emissivity model. Results are compared to retrieved values from the AMSR-E passive microwave observations for cloud-free scenes over a 6-year period. The resulting emissivities are compared in the context of surface properties including surface temperature, leaf area index, soil moisture, and precipitation. The comparison indicates that lower frequency channels respond most directly to the surface soil and its dielectric properties. Differences between retrieved and modeled emissivity are generally less than 2-3% and appear to be a function of soil moisture and LAI at frequencies less than 37 GHz. Agreement is better for the vertical polarization channels. At 89 GHz, a large difference is present between retrieved and modeled emissivity in both mean and magnitude of variability. Problems are likely present at higher microwave frequencies in both calculations and more work is required to understand land surface emissivity in these channels.