Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p51c..07c&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P51C-07
Other
5464 Remote Sensing, 5470 Surface Materials And Properties
Scientific paper
Observations made by the ISM instrument on the Phobos II spacecraft provided evidence for martian crustal rock compositions similar to basaltic SNC meteorites. These meteorites contain both ortho- and clino-pyroxene. Analyses of 1 and 2 μm spectral bands showed varying proportions of these two minerals over the low albedo regions observed by ISM. Pyroxene is also observed in TES data using mineral deconvolution models of the thermal emission spectra. Different models disagree on whether there are one or two pyroxenes present in surface materials. The disconnect between ISM and TES observations may result from several issues including differences in interactions of radiation with the surface in the two wavelength ranges, incomplete mineral modeling of TES data due to spectral library limitations, or differences in the surface due to the ten year separation between the missions. An important concern is how visible and near-infrared radiation interact with the surface compared to the way thermal energy is emitted. Thin coatings on the rocks in Syrtis Major were suspected based on spectral slope variability in the ISM data. It is possible that these coatings respond differently in the thermal infrared and affect the interpretation of mineral composition. We address these issues by comparing ISM and TES spectral data directly. The two data sets were gridded and coregistered to a 0.5° resolution. The spectra were then merged to make an extended spectral set covering both wavelength ranges. By comparing the spectral parameters from the near-infrared (ISM) with the mineral deconvolutions, surface-type deconvolutions, and spectral shapes from the thermal infrared (TES), we can learn more about the nature of the surface materials. This work in particular looks at the relationship between the 1 and 2 μm bands and mineral deconvolution-derived pyroxene content. As expected, these quantities are correlated. However, variations in the pyroxene to plagioclase ratio do not correlate well with pyroxene band strength, whereas blackbody amounts are strongly anti-correlated with the vis-NIR bands. Normalizing the mineral abundances by removing the blackbody fraction destroys the correlation between the pyroxene and the vis-NIR aborptions. This suggests that variations in mineral compositions of rocks are not as important as areal mixing on the surface with dust or other thermally neutral materials in controlling the vis-NIR absorptions. Variations in vis-NIR parameters (such as slope) in the Syrtis region have no counterpart variations in the thermal spectra. The relationship between vis-NIR spectral slope and mineral deconvolution results will be further explored in order to try to address whether rock coatings are controlling this disconnect. Differences in the vis-NIR to thermal correspondance between Valles Marineris and Syrtis Major will be addressed by further modeling.
Cooper Donald C.
Mustard John F.
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