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Updated Radiative Transfer Model for Titan: Validation on VIMS/Cassini Observations of the Huygens Landing Site and Application to the Analysis of the Dragonfly Landing Area
  • +8
  • Maël Es-Sayeh,
  • Sebastien Rodriguez,
  • Thomas Cornet,
  • Luca Maltagliati,
  • Maélie Coutelier,
  • Pascal Rannou,
  • Bjorn Grieger,
  • Erich Karkoschka,
  • Benoit Seignovert,
  • Stephane Le Mouelic,
  • Christophe Sotin
Maël Es-Sayeh
Université de Paris

Corresponding Author:essayeh@ipgp.fr

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Sebastien Rodriguez
Université de Paris, Institut de physique du globe de Paris, CNRS
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Thomas Cornet
European Space Agency
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Luca Maltagliati
Nature Astronomy, Springer Nature
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Maélie Coutelier
GSMA - University of Reims Champagne-Ardennes
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Pascal Rannou
GSMA - University of Reims Champagne-Ardennes
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Bjorn Grieger
European Space Agency
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Erich Karkoschka
University of Arizona
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Benoit Seignovert
LPGN Laboratoire de Planétologie et Géodynamique de Nantes
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Stephane Le Mouelic
LPG Nantes, UMR 6112, CNRS, OSUNA, Université de Nantes
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Christophe Sotin
LPGN Laboratoire de Planétologie et Géodynamique de Nantes
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Abstract

Titan is a prime target for astrobiological research. Organic materials from atmospheric chemistry precipitate on the surface and are subject to geological processes (e.g. eolian and fluvial erosion) that lead to the formation of dune fields, river networks and seas similar to their terrestrial counterparts. The analysis of the surface reflectance in the near-infrared (NIR) allows to constrain the surface composition, which is crucial to understand these atmosphere/surface interactions. However, Titan’s atmosphere prevents the surface from being probed in the NIR, except in 7 transmission windows where the methane absorption is sufficiently low (centered at 0.93, 1.08, 1.27, 1.59, 2.01, 2.7- 2.8 and 5 μm). We use an updated version of the Radiative Transfer (RT) model of Hirtzig et al. (2013), with updated gases and aerosols opacities, in order to better simulate atmospheric absorption and scattering and retrieve surface albedos in the 7 NIR transmission windows with an enhanced accuracy. Our RT model is based on the SHDOMPP and CDISORT (Evans, 2007 and Buras, 2011) solvers to solve the RT equations in plane-parallel and pseudo-spherical approximations respectively. We recently improved atmospheric inputs of the model with up-to-date gaseous CH4, CH3D, 13CH4, C2H2, HCN and CO abundances profiles and absorption coefficients (Vinatier et al. 2007, Niemann et al. 2010; Maltagliati et al. 2015; Serigano et al. 2016; Rey et al. 2018; Thelen et al. 2019; Gautier et al. 2021), and improved aerosol optical properties. In particular, optical properties of Titan’s aerosols are now computed from a fractal aggregate model (Rannou et al. 2003) constrained by measurements of the Huygens probe (Tomasko et al. 2008 and Doose et al. 2016). The new version of our RT model is benchmarked with the help of the most recent RT model for Titan (Coutelier et al. 2021) and validated using observations of the Descent Imager/Spectral Radiometer (DISR) onboard Huygens. Coupled with an efficient inversion scheme, our model can be apply to the Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) dataset to retrieve atmospheric opacity and surface albedos at regional and global scales. This will help to analyze future James Webb Space Telescope (JWST) observations of Titan (Nixon et al. 2016) and prepare the Dragonfly mission (Lorenz et al. 2018).