P13B-2132
Computing Global Mosaics of Titan With the VIMS Imaging Spectrometer
Monday, 14 December 2015
Poster Hall (Moscone South)
Stephane Le Mouelic1, Thomas Cornet2, Sebastien Rodriguez3, Christophe Sotin4, Jason W Barnes5, Robert Hamilton Brown6, Kevin H Baines7, Bonnie J Buratti4, Roger Nelson Clark8 and Philip D Nicholson9, (1)CNRS, Paris Cedex 16, France, (2)European Space Agency, Villanueva De La Can, Spain, (3)AIM - CEA/CNRS/Uni. P7, Gif/Yvette, France, (4)NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (5)University of Idaho, Moscow, ID, United States, (6)University of Arizona, Tucson, AZ, United States, (7)Jet Propulsion Laboratory, Pasadena, CA, United States, (8)Planetary Science Institute Tucson, Tucson, AZ, United States, (9)Cornell University, Ithaca, NY, United States
Abstract:
The Visual and Infrared Mapping Spectrometer (VIMS) onboard Cassini observes 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. We have produced a global hyperspectral mosaic of the complete VIMS data set of Titan between T0 (July 2004) and T112 flyby (July 2015), by merging all the data cubes sorted by increasing spatial resolution, with the high resolution images on top of the mosaic and the low resolution images used as background. We filtered out the observing geometry in order to remove the pixels acquired in too extreme illuminating and viewing conditions, which systematically produce atmospheric artifacts. We used thresholds of 80° both on the incidence and emission angles, 100° on the phase angle, and 7 on the airmass. These thresholds corresponds to a trade-off between surface coverage and data quality. The viewing geometry is normalized at first order using a surface photometric function derived from the observation at 5 µm, where the atmospheric scattering is almost negligible. We also use the wings of the atmospheric windows as a proxy to correct for the amount of additive scattering present in the center of these windows, where the surface is seen by VIMS. Various color composites can then be produced using combinations of different wavelengths to emphasize surface heterogeneities. Among these, a RGB composite with red controlled by the 5 µm image, the green by the 2 µm image and the blue by the 1.27 µm, reveals the extent of equatorial dune fields appearing in brownish tones. Bluish areas corresponds to regions possibly enriched in water ice or other organic compounds. Composite of band ratios such as 1.59/1.27 µm, 2.03/1.27 µm and 1.27/1.08 also prove to be more useful to better emphasize surface variations, even if they are also more sensitive to residual artefacts due to atmospheric and geometric effects or calibration residuals.
