VERIFICATION OF SPECTRAL MAPPING OF THE MCMURDO DRY VALLEYS USING IN SITU AND LABORATORY TECHNIQUES
We present the initial compositional mapping results of the MDV using a combination of reflectance and emission spectroscopic datasets from the ALI and ASTER instruments. The orbital datasets are atmospherically corrected using standard methods and the lithologic units mapped on the basis of ferric and ferrous electronic absorptions for visible-near infrared wavelengths and restrahlen absorptions in mid-infrared wavelengths. The mapping captures the mineralogic diversity present within the different lithologies across the MDV as well as alteration rinds. In addition, spectroscopic analyses highlight subtle compositional variations that cannot be readily observed using standard geologic mapping techniques.
Over two field seasons, 48 sample grids were collected across the MDV, each composed of nine rock and soil samples (total of 432 samples). Subsets of these sample grids were spectrally characterized using visible/near-infrared and thermal-infrared laboratory instruments. Particular emphasis was put on the development and spectral signatures of alteration rinds and coatings, which could alter the spectral signatures and, consequently, the interpretation of these spectral and orbital datasets. These measurements were then used to verify orbital observations and to assess surface compositions in regions that were not directly sampled. The laboratory analyses of mafic rocks show that the spectral signatures of the rock exteriors are dominated by oxidation and rind development that shows strong component of silica that is not reflected in the chemistry of the interiors and are best modeled by low water:rock ratio alteration processes.