Photometric Modeling and VIS-IR Albedo Maps of Tethys From Cassini-VIMS

Abstract

We report about the derivation of visible (VIS) and infrared (IR) albedo maps and spectral indicators of Saturn's satellite Tethys from the complete Cassini-Visual and Infrared Mapping Spectrometer (VIMS) data set. The application of a photometric correction is necessary to remove illumination and viewing effects from the I/F spectra, to compute spectral albedo and to correctly associate spectral variations to changes in composition or physical properties of the surface. In this work we are adopting the photometric correction proposed by Shkuratov et al. (2011, <A href="https://doi.org/10.1016/j.pss.2011.06.011">https://doi.org/10.1016/j.pss.2011.06.011</A>) to derive albedo maps of Tethys from disk-resolved Cassini-VIMS data. After having applied a similar methodology to Dione's data (Filacchione et al., 2018, <A href="https://doi.org/10.1002/2017GL076869">https://doi.org/10.1002/2017GL076869</A>), we present here the results achieved for Tethys: surface albedo maps and photometric parameters are computed at five visible (0.35, 0.44, 0.55, 0.70, and 0.95 μm) and five infrared (1.046, 1.540, 1.822, 2.050, and 2.200 μm) wavelengths and rendered in cylindrical projection with a 0.5° × 0.5° angular resolution in latitude and longitude, corresponding to a highest spatial resolution of 4.7 km/bin. The 0.35- to 0.55- and 0.55- to 0.95-μm spectral slopes and the water ice 2.050-μm band depth maps are computed after having applied the photometric correction, in order to trace the leading-trailing hemisphere dichotomy, to constrain the shape of the equatorial lens generated by the bombardment of high-energy magnetospheric electrons on the leading hemisphere, and to observe the stronger water ice band depth and reddening within the floors of Odysseus and Penelope impact craters.