A TEMPERATURE AND EMISSIVITY SEPARATION ALGORITHM FOR ADVANCED SPACEBORNE THERMAL EMISSION AND REFLECTION RADIOMETER (ASTER) IMAGES

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (AS TER) scanner on NASA's Earth Observing System (EOS)-AM1 satellite (lau nch scheduled for 1998) will collect five bands of thermal infrared (T IR) data with a noise equivalent temperature difference (NE Delta T) o f less than or equal to 0.3 K to estimate surface temperatures and emi ssivity spectra, especially over land, where emissivities are not know n in advance, Temperature/emissivity separation (TES) is difficult bec ause there are five measurements but six unknowns. Various approaches have been used to constrain the extra degree of freedom, ASTER's TES a lgorithm hybridizes three established algorithms, first estimating the normalized emissivities and then calculating emissivity band ratios, An empirical relationship predicts the minimum emissivity from the spe ctral contrast of the ratioed values, permitting recovery of the emiss ivity spectrum. TES uses an iterative approach to remove reflected sky irradiance. Based on numerical simulation, TES should he able to reco ver temperatures within about +/-1.5 K and emissivities within about /-0.015, Validation using airborne simulator images taken over playas and ponds in central Nevada demonstrates that, with proper atmospheric compensation, it is possible to meet the theoretical expectations, Th e main sources of uncertainty in the output temperature and emissivity images are the empirical relationship between emissivity values and s pectral contrast, compensation for reflected sky irradiance, and ASTER 's precision, calibration, and atmospheric compensation.