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Abstract: Knowledge of the Land Surface Emissivity (LSE) in the Thermal Infrared (TIR: 8–12µm) part of the electromagnetic spectrum is essential to derive accurate Land Surface Temperatures (LSTs) from spaceborne TIR measurements. This study focuses on validation of the emissivity product in the North American ASTER Land Surface Emissivity Database (NAALSED) v2.0 — a mean seasonal, gridded emissivity product produced at 100m spatial resolution using all Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scenes from 2000 to 2008 over North America (http://emissivity.jpl.nasa.gov). The NAALSED emissivity product was validated over bare surfaces with laboratory measurements of sand samples collected at nine pseudo-invariant sand dune sites located in the western/southwestern USA. The nine sand dune sites cover a broad range of surface emissivities in the TIR. Results show that the absolute mean emissivity difference between NAALSED and the laboratory results for the nine validation sites and all five ASTER TIR bands was 0.016 (1.6%). This emissivity difference is equivalent to approximately a 1K error in the land surface temperature for a material at 300K in the TIR. [Copyright &y& Elsevier]

Abstract: Thermal Infrared (TIR) data are supplied by instruments on several satellite platforms including the Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER), which was launched on the Terra satellite in 1999. ASTER has five bands in the TIR and a spatial resolution of 90 m. A mean seasonal, gridded, Land Surface Temperature and Emissivity (LST&E) database has been produced at 100 m spatial resolution using all the ASTER scenes acquired for the months of Jan–Mar (winter) and Jul–Sep (summer) over North America. Version 2.0 of the North American ASTER Land Surface Database (NAALSED) (http://emissivity.jpl.nasa.gov) has now been released and includes two key refinements designed to improve the accuracy of emissivities over water bodies and account for the effects of fractional vegetation cover. The water adjustment replaces ASTER emissivity values over inland water bodies with a measured library emissivity spectrum of distilled water, and then re-calculates the surface temperatures using a split-window algorithm. The accuracy of ASTER emissivities over vegetated surfaces is improved by applying a fractional vegetation cover adjustment (TES_Pv) to the ASTER Temperature Emissivity Separation (TES) calibration curve. Comparisons of NAALSED emissivity spectra with in-situ data measured over a grassland in Northern Texas resulted in a combined absolute difference for all five ASTER bands of 1.0% for the summer emissivity data, and 0.1% for the winter data—a 33–50% improvement over the original TES results. [Copyright &y& Elsevier]