UV-Visible reflectance of Phobos from SPICAM and OMEGA and comparison with Deimos
Résumé
Mars Express made several encounters with Phobos and a few with Deimos since 2004. Observa- tions with SPICAM and OMEGA imaging spectrometers on board Mars Express covers the range from UV (110-312 nm) to visible and mid IR up to 5 μm. In the following we con- sider the ultraviolet (UV) channel of SPICAM and only the visible channel of OMEGA and its small UV extension down to 390 nm, in order to compare with SPICAM. Preliminary results were presented already in the past, e.g.[1]. Since then, a more detailed analysis was carried out, subtracting some internally scattered light affecting the SPICAM UV retrieved reflectance. Figure 1 shows the Phobos spectrum recorded by SPICAM at orbit 748 on August 20, 2004, at a low phase angle of 22° and 1248 km distance. Large oscillations ob- served in the spectrum are of solar origin. The subtracted stray light accounts for about 25% of the original spectrum. If not correctly accounted for, it would induce spurious oscil- lations in the reflectance spectrum.
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