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Titan’s surface at 2.18-cm wavelength imaged by the Cassini RADAR radiometer: Results and interpretations through the first ten years of observation

Michael A. Janssen 1 Alice Le Gall 2, 3 Rosaly M. Lopes 1 Ralph D. Lorenz 4 Mike J. Malaska 1 Alexander G. Hayes 5 C.D. Neish 6 Anezina Solomonidou 1 K.L. Mitchell 1 J. Radebaugh 7 Steve J. Keihm 1 Mathieu Choukroun 1 Cédric Leyrat 8 Pierre J. Encrenaz 9 M. Mastrogiuseppe 10
1 JPL - Jet Propulsion Laboratory
2 IMPEC - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
3 ESTER - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
4 APL - Johns Hopkins University Applied Physics Laboratory [Laurel, MD]
5 Department of Astronomy [Ithaca]
6 Department of Physics and Space Sciences [FIT]
7 Department of Geological Sciences [BYU]
8 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
9 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
10 DIET - Dipartimento di Ingegneria dell'Informazione, Elettronica e Telecomunicazioni [Roma]
Abstract : A comprehensive calibration and mapping of the thermal microwave emission from Titan’s surface is reported based on radiometric data obtained at 2.18-cm wavelength by the passive radiometer included in the Cassini RADAR instrument. Compared to previous work, the present results incorporate the much larger data set obtained in the approximately ten years following Saturn Orbit Insertion. Brightness temperature data including polarization were accumulated by segments in Titan passes from Ta (October 2004) through T98 (February 2014). The observational segments were analyzed to produce a mosaic of effective dielectric constant based on the measurement of thermal polarization covering 76% of the surface, and brightness temperature at normal incidence covering Titan’s entire surface. As part of the mosaicking process we also solved for the seasonal variation of physical temperature with latitude, which we found to be smaller by a factor of 0.87 ± 0.05 in relative amplitude compared to that reported in the thermal infrared by Cassini’s Composite Infrared Spectrometer (CIRS). We used the equatorial temperature obtained by the Huygens probe and the seasonal dependence with latitude from CIRS to convert the brightness mosaic to absolute emissivity, from which we could infer global thermophysical properties of the surface in combination with the dielectric mosaic. We see strong evidence for subsurface (volume) scattering as a dominant cause of the radar reflectivity in bright regions, and elsewhere a surface composition consistent with the slow deposition and processing of organic compounds from the atmosphere. The presence of water ice in the near subsurface is strongly indicated by the high degree of volume scattering observed in radar-bright regions (e.g., Hummocky/mountainous terrains) constituting ∼ 10% of Titan’s surface. A thermal analysis allowed us to infer a mean 2.18-cm emission depth in the range 40 to 100 cm for the dominant radar-dark terrains (the remainder of Titan’s surface) at all latitudes of Titan, consistent with the deposition and possible processing and redistribution of tholin-like atmospheric photochemical products.
Keywords : Composition Radio observations Satellites Surface Titan Surfaces
Document type :
Journal articles
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https://hal-insu.archives-ouvertes.fr/insu-01206401
Contributor : Catherine Cardon <>
Submitted on : Tuesday, September 29, 2015 - 8:10:58 AM
Last modification on : Saturday, December 12, 2020 - 12:10:04 PM

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INSU | CNRS | UNIV-PARIS7 | UNIV-CERGY | OBSPM | LERMA | LESIA | UPMC | ENS-PARIS | UVSQ | LATMOS | USPC | SORBONNE-UNIVERSITE | SU-SCIENCES | UNIV-PARIS | UP-SCIENCES | PSL

Citation

Michael A. Janssen, Alice Le Gall, Rosaly M. Lopes, Ralph D. Lorenz, Mike J. Malaska, et al.. Titan’s surface at 2.18-cm wavelength imaged by the Cassini RADAR radiometer: Results and interpretations through the first ten years of observation. Icarus, Elsevier, 2016, 270, pp.443-459. ⟨10.1016/j.icarus.2015.09.027⟩. ⟨insu-01206401⟩

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