A Cassini VIMS data portal for Titan and Saturn's icy satellites

The Cassini spacecraft orbited Saturn between 2004 and 2017, taking a wealth of data of the planet and its icy moons. We have completed a setup providing user-friendly access to the scientific content of the complete Visual and Infrared Mapping Spectrometer (VIMS) data archive of Saturn's main moons.

VIMS acquired images up to 64x64 pixels wide in 352 spectral channels from 0.35 to 5.12 µm, using two separate instruments [1]. Titan and the icy moons were observed both during targeted and non targeted flybys, representing several tens of thousands of individual data cubes. One of the main challenges with such a big data set is to provide tools to search and identify the most interesting data. For this purpose, we have set up a dedicated website (vims.univ-nantes.fr) which provides the ability to display false color browse products of the main moons: Titan, Enceladus, Dione, Rhea, Phoebe, Thetys, Hyperion, Iapetus.

VIMS raw data coming from the Planetary Data System archive have been radiometrically calibrated using the USGS digital image processing software package ISIS3. The applied calibration corresponds to version "RC19" of the VIMS calibration pipeline [2]. The geometric navigation information has then been added using SPICE routines to extract spacecraft and planetary ephemerides, and event kernels.

The VIMS data set of Titan contains a wealth of information both concerning the surface and atmospheric properties. Whereas the surface of Titan can only be seen in 7 infrared windows at 1.08, 1.27, 1.59, 2.03, 2.69, 2.78 and 5 µm [3], these wavelengths can eventually be combined to reveal the spectral heterogeneities of the surface. Other wavelengths are also useful to emphasize atmospheric properties such as clouds, haze, methane fluorescence. When selecting a targeted or non-targeted flyby on the main entrance page of the website, the user is redirected to secondary pages showing previews of all the VIMS cubes acquired during this flyby, with the possibility to choose between several RGB combinations for their visualization [4]. This makes straightforward to visually identify both the quality and the potential scientific content of each of the cubes. A similar approach has been developed for the other icy satellites. Such an archive could be useful to study the regions that will be potentially explored by the forthcoming Dragonfly mission to Titan.

[1] Brown, R. H., et al., Space Sci. Rev. 115, 111-168, 2004. [2] Clark, R. N et al., the VIMS Wavelength and Radiometric Calibration 19, Final Report, PDS, 2018. [3] Sotin, C. et al., Nature, p786-789, 2005. [4] Le Mouélic, S. et al., Icarus, 319, 121-132, 2019.