Empirical Approaches To Reduce The Atmospheric Component In VIMS Surface Images Of Titan

Details Empirical Approaches To Reduce The Atmospheric Component In VIMS Surface Images Of Titan Empirical Approaches To Reduce The Atmospheric Component In VIMS Surface Images Of Titan

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p31c1546l&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #P31C-1546

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[0540] Computational Geophysics / Image Processing, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6281] Planetary Sciences: Solar System Objects / Titan, [6297] Planetary Sciences: Solar System Objects / Instruments And Techniques

Scientific paper

The Visual and Infrared Mapping Spectrometer (VIMS) onboard Cassini can see the surface of Titan in seven narrow atmospheric windows in the infrared at 0.93, 1.08, 1.27, 1.59, 2.01, 2.68-2.78, and 4.9-5.1 microns. In addition to the strong absorption by atmospheric gases (mainly methane and nitrogen), the presence of aerosols in the atmosphere blurs the images at short wavelengths due to a very strong scattering effect, which acts as an additive component to the signal coming from the surface. We have produced a global hyperspectral mosaic of the complete VIMS archive between T0 (July 2004) and T66 flyby (January 2010), by merging all the data cubes sorted by increasing spatial resolution in order to put the high resolution images on top and to use the low resolution images as background. We filtered out the observing geometry in order to remove the pixels acquired in too extreme illuminating and viewing conditions, which systematically amplify the atmospheric artifacts. We used thresholds of 80° both on the incidence and emission angles, and 100° on the phase angle. We first focused our study on the 5 microns window, where the additive component from the haze scattering is negligible, in order to investigate the multiplicative factor which should be used to normalize the viewing geometry between all flybys, and thus to reconcile observations acquired in very different viewing conditions. Indeed, if we exclude transient phenomena (mainly clouds and possible surface changes), the seams between all individual images should disappear after correction. We then investigated other windows at shorter wavelengths, where the additive scattering component cannot be neglected. We found that the wings of the atmospheric windows can be used as a proxy for the amount of additive scattering present in the center of these windows, where the surface is best seen by VIMS. In the band wings, the solar flux never reaches the ground. The corresponding signal therefore gives the contribution of the upper layers of the atmosphere, which is also present in the center of the atmospheric window (which probes the full atmospheric path up to the surface). The ultimate goal would be to produce homogeneous mosaics in each surface window corrected from the additive scattering component, in order to use the band ratio technique. Band ratios emphasize very subtle compositional heterogeneities provided that no additive component is present in the numerator and denominator. Examples will be given at the meeting.

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