The North American ASTER Land Surface Emissivity Database (NAALSED) Version 2.0

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.