Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p53b1445l&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P53B-1445
Physics
5400 Planetary Sciences: Solid Surface Planets, 5464 Remote Sensing, 5494 Instruments And Techniques, 6225 Mars
Scientific paper
Since December 2003, the OMEGA imaging spectrometer onboard Mars Express has completed a near global coverage of Mars in 352 spectral channels from 0.3 to 5.2 µm. The data set covers two martian years. We have analyzed the global data set (up to orbit 5200) with an automated linear unmixing algorithm (MELSUM) which is described in Combe et al. (Planet. Space. Sci., 2008). In this approach, we seek for each OMEGA pixel the best linear combination of a suite of laboratory spectra of pure minerals covering the main families (mafics, sulfates, oxides, carbonates, phyllosilicates). Two ices endmembers (H20 and CO2) are included in the input library to account for atmospheric clouds and surface frost. Artificial pure slopes endmembers complement the spectral library in order to correct at first order for scattering and grain size effects. Global distribution maps have been produced for each of the endmembers in the input library. One of the challenges in computing these maps (representing ~500 GB of raw data), is to filter the data in order to account for the variations in atmospheric conditions, viewing geometry, seasonal frost or dust cover, and instrumental effects. Several filters have been used, such as an ice detection criterion, a spectrum quality index, an incidence angle threshold, and the Root Mean Square residue of the linear unmixing algorithm. This provides homogeneous maps of the distribution of the main mineral families. Clinopyroxenes and orthopyroxenes are found mostly in the southern hemisphere, which is consistent with previous studies. Olivine is found in very localized spots such as Nili Fossae or Nili Patera. Iron oxides appear with a low signal in the northern bright areas, and with a very strong signal in localized areas such as Aram Chaos and Meridiani Planum over light toned layered deposits, or in their vicinity. The Ferrihydrite endmember map indicates a possible occurrence of this mineral in northern Meridiani Planum and in Aram Chaos, and in the oldest terrains surrounding Syrtis Major.
Bibring J.
Bourgeois Olivier
Christophe Soulé
Combe J.
Gondet Brigitte
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