OBSERVATION OF 3 μm HYDRATION FEATURE ON MARS FROM OMEGA-MEx DATA
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چکیده
Introduction: The OMEGA investigation, on board the ESA Mars Express mission, is to map Mars’ surface at a 0.3to 5-kilometer resolution using visible-infrared hyperspectral reflectance imagery. After numerous results on Mars surface diversity using the C channel (1.0 to 2.5 μm) [1], this paper reports a systematic reduction of the OMEGA data in the L channel (spectral range 2.5 to 5.1 μm). This global reduction gives the opportunity to study surface hydration through the 3 μm absorption band, which is indistinctly due to bending and stretching vibrations of water bound in minerals or adsorbed at their surface, and of hydroxyl groups [2]. Compared to previous studies based on ISM (Phobos spacecraft) [3] and IRS (Mariner 6 and 7 spacecrafts) [4], OMEGA dataset provides a larger coverage investigation, with a better signal to noise ratio, and a better spatial resolution. This type of hydration is very important to know how alteration currently plays, and should provide clues for the geologic and climatic history of Mars. Thermal removal: A typical OMEGA spectrum can be modelled as the summation of two components: the reflexion of the solar light and the thermal emission, both being filtered by the atmosphere. In this study surface reflection is assumed to be lambertian. As Mars surface temperature may reach 300K, the L channel is in a range of wavelengths where thermal emission from the surface cannot be neglected. We need therefore to assess the temperature of each pixel and to remove the thermal emission to compare OMEGA albedo spectra to laboratory data.
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تاریخ انتشار 2006