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R.N. Clark, T.M. Hoefen (U. S. Geological Survey)
The Mars Global Surveyor Thermal Emission Spectrometer (TES) has been obtaining 6.25-50 micron thermal emission spectra with an approximately 3x6 km footprint for nearly two years, with a majority of the planet's surface measured. The TES spectra contain 143 channels with about 10 wavenumber sampling. The TES footprint is 3 pixels wide, providing planetary coverage in narrow strips 9 km wide. The TES spectra have been assembled into image cubes covering approximately 45 degrees of longitude and latitude with 16 pixels per degree. These image cubes were converted to emissivity and searches for specific spectral features were conducted. The spatial context of hyperspectral image cubes can help verify the existence of a spectral feature that is close to the noise limit, and can help separate atmospheric from surface origins. Atmospheric features generally are spatially diffuse except at large topographic boundaries, such as the rim of Valles Marineris. Features due to surface minerals follow geologic boundaries. Spectral features, some as yet mineralogically unidentified, show general correlation with the bright/dark albedo boundaries and include features at 7.3, 8.1 and 21.5 microns, with a possible feature near 12.8 microns. As previously reported, no carbonate deposits have been found. Several features may show strong depths in isolated pixels and may indicate small deposits. While these could be noise, repeat coverage may allow proof of their existence. Spectral features in the 20-30 micron region include the hematite zone (Christensen et al, JGR 2000, e.g. near 25.5 microns) and the Nili Fossea zone (Hoefen et al, DPS 2000). RGB color combinations of spectral feature depths and visual albedo provide new unit maps.
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