The North American ASTER Land Surface Emissivity Database (NAALSED) V2.0

One of the key Earth Science Data Records identified by NASA is Land Surface Temperature and Emissivity (LST&E). LST&E data are important parameters in global climate change studies that involve climate modeling, ice dynamic analyses, surface-atmosphere interactions and land use, land cover change. Accurate knowledge of the Land Surface Emissivity (LSE) in the Thermal Infrared (TIR: 8-12 um) part of the electromagnetic spectrum is essential to derive accurate Land Surface Temperatures (LSTs) from spaceborne TIR measurements. TIR data are supplied by instruments on several satellite platforms including the Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER), which was launched on NASA's Terra satellite in 1999. ASTER has five bands in the TIR and a spatial resolution of 90 m. A mean seasonal, gridded, 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 LSE's over water bodies and account for the effects of fractional vegetation cover. The water adjustment replaces ASTER LSE 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 LSE over vegetated surfaces is improved by applying a fractional vegetation cover adjustment (TES_Pv) to the ASTER Temperature Emissivity Separation (TES) calibration curve. The NAALSED LSE 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 LSE's in the TIR. Results show that the absolute mean LSE difference between NAALSED and the laboratory results for the nine validation sites and all five ASTER TIR bands was 0.016 (1.6 %). This LSE difference is equivalent to approximately a 1 K error in the LST for a material at 300 K in the TIR.