DPS 2001 meeting, November 2001
Session 36. Mars Surface Posters
Displayed, 9:00am Tuesday - 3:00pm Saturday, Highlighted, Friday, November 30, 2001, 9:00-10:30am, French Market Exhibit Hall

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[36.03] Correcting Martian spectra for illumination effects

M.T. Lemmon (Texas A&M University), K.E. Herkenhoff, J.R. Johnson (USGS), P.H. Smith (Univerisity of Arizona)

With very few exceptions, a Martian rock sits under a Martian sky. The same simple fact is true of Martian soils. So, when spectra are used to investigate the composition of Martian rocks and soils, the sky illumination must be understood and compensated for. The Mars Pathfinder imaging experiment included ways to perform a simple but good illumination-correction for level targets. In addition, several sky measurements allowed a more detailed model of sky illumination to be created and applied to the correction of spectra.

We use a radiative-transfer model of atmospheric scattering to derive sky illumination for arbitrary IMP images. The model works well in comparison with 12-color images of the radiative calibration targets on Pathfinder. We demonstrate the spectral effect of comparing a spectrum of a level target with one of a tilted target. We show that the commonly used target corrections work well for comparing images of level objects at varying times of day, but we will present limitations to the method. Since even soil surfaces at Ares Vallis are not precisely level, we investigate spectral uncertainties that result from small, arbitrary tilts. We illustrate a correction procedure that uses the illumination and topographic models to correct spectra. Application of the same procedure to orbital data is also illustrated, and can be done when there are known constraints on atmospheric dust opacity and scattering properties.

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