Evaluating a satellite-derived global infrared land surface emissivity data set for use in radiative transfer modeling

Radiative transfer models rely on accurate atmospheric and surface conditions for simulating top-of-atmosphere satellite radiance. Over land surfaces, emissivity is especially important for simulating surface-sensitive channels, owing to its spatial and temporal variability. In this study, the University of Wisconsin Global Infrared Land Surface Emissivity Database (UWIREMIS) has been evaluated in the Community Radiative Transfer Model (CRTM). Radiative transfer simulations of top-of-atmosphere Spinning Enhanced Visible and Infrared Imager (SEVIRI) brightness temperature have been compared to actual SEVIRI brightness temperature observations for 30 May 2010 at 0000 UTC, using both the UWIREMIS and the current internal CRTM emissivity data sets as surface input to CRTM. When using UWIREMIS, a brightness temperature bias of -0.85 K for the SEVIRI 8.7 mu m channel is due in part to excellent characterization of the emissivity spectrum for bare ground surfaces in this spectral region, compared to a bias of -2.55 K when using the existing CRTM emissivity. Additionally, UWIREMIS has been compared to the North American ASTER Land Surface Emissivity Database (NAALSED), a validated land surface emissivity data set, and low emissivity biases of 0.004 (summer) and 0.007 (winter) indicate UWIREMIS accuracy for the NAALSED spatial domain and the spectral region of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) channels. With its high spectral and high spatial resolution, UWIREMIS is well suited for providing the infrared surface emissivity contribution to radiative transfer models. Additional work will be needed to assess UWIREMIS for more spectral regions, surface types, and time periods.