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Cassini SAR, radiometry, scatterometry and altimetry observations of Titan's dune fields

Le Gall, A. and Janssen, M. A. and Wye, L. C. and Hayes, A. G. and Radebaugh, J. and Savage, C. and Zebker, H. and Lorenz, R. D. and Lunine, J. I. and Kirk, R. L. and Lopes, R. M. C. and Wall, S. and Callahan, P. and Stofan, E. R. and Farr, T. (2011) Cassini SAR, radiometry, scatterometry and altimetry observations of Titan's dune fields. Icarus, 213 (2). pp. 608-624. ISSN 0019-1035. https://resolver.caltech.edu/CaltechAUTHORS:20110628-094704375

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Abstract

Large expanses of linear dunes cover Titan’s equatorial regions. As the Cassini mission continues, more dune fields are becoming unveiled and examined by the microwave radar in all its modes of operation (SAR, radiometry, scatterometry, altimetry) and with an increasing variety of observational geometries. In this paper, we report on Cassini’s radar instrument observations of the dune fields mapped through May 2009 and present our key findings in terms of Titan’s geology and climate. We estimate that dune fields cover ~12.5% of Titan’s surface, which corresponds to an area of ~10 million km^2, roughly the area of the United States. If dune sand-sized particles are mainly composed of solid organics as suggested by VIMS observations (Cassini Visual and Infrared Mapping Spectrometer) and atmospheric modeling and supported by radiometry data, dune fields are the largest known organic reservoir on Titan. Dune regions are, with the exception of the polar lakes and seas, the least reflective and most emissive features on this moon. Interestingly, we also find a latitudinal dependence in the dune field microwave properties: up to a latitude of ~11°, dune fields tend to become less emissive and brighter as one moves northward. Above ~11° this trend is reversed. The microwave signatures of the dune regions are thought to be primarily controlled by the interdune proportion (relative to that of the dune), roughness and degree of sand cover. In agreement with radiometry and scatterometry observations, SAR images suggest that the fraction of interdunes increases northward up to a latitude of ~14°. In general, scattering from the subsurface (volume scattering and surface scattering from buried interfaces) makes interdunal regions brighter than the dunes. The observed latitudinal trend may therefore also be partially caused by a gradual thinning of the interdunal sand cover or surrounding sand sheets to the north, thus allowing wave penetration in the underlying substrate. Altimetry measurements over dunes have highlighted a region located in the Fensal dune field (~5° latitude) where the icy bedrock of Titan is likely exposed within smooth interdune areas. The hemispherical assymetry of dune field properties may point to a general reduction in the availability of sediments and/or an increase in the ground humidity toward the north, which could be related to Titan’s asymmetric seasonal polar insolation. Alternatively, it may indicate that either the wind pattern or the topography is less favorable for dune formation in Titan’s northern tropics.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.icarus.2011.03.026DOIArticle
http://www.sciencedirect.com/science/article/pii/S0019103511001175PublisherArticle
ORCID:
AuthorORCID
Janssen, M. A.0000-0001-5476-731X
Additional Information:© 2011 Elsevier Inc. Received 8 December 2010; revised 22 March 2011; accepted 27 March 2011. Available online 7 April 2011. This work was supported by the Cassini/Huygens mission, which is a joint endeavor of NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) and is managed by JPL/Caltech under a contract with NASA. A. Le Gall is supported by the NASA Postdoctoral Program, administrated by Oak Ridge Associated Universities (ORAU). The authors are grateful to Don Jennings for sharing his CIRS measurements of the latitudinal ground temperature distribution. They also wish to thank Philippe Paillou for discussion on the definition of the terms used in the present paper to describe scattering from the dune fields and Dave Rubin for his thorough review of the manuscript.
Funders:
Funding AgencyGrant Number
Cassini/Huygens Mission UNSPECIFIED
NASAUNSPECIFIED
European Space Agency (ESA) UNSPECIFIED
Agenzia Spaziale Italiana (ASI)UNSPECIFIED
Subject Keywords:Titan; Radar observations; Radio observations; Geological processes
Issue or Number:2
Record Number:CaltechAUTHORS:20110628-094704375
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20110628-094704375
Official Citation:A. Le Gall, M.A. Janssen, L.C. Wye, A.G. Hayes, J. Radebaugh, C. Savage, H. Zebker, R.D. Lorenz, J.I. Lunine, R.L. Kirk, R.M.C. Lopes, S. Wall, P. Callahan, E.R. Stofan, T. Farr and the Cassini Radar Team, Cassini SAR, radiometry, scatterometry and altimetry observations of Titan's dune fields, Icarus, Volume 213, Issue 2, June 2011, Pages 608-624, ISSN 0019-1035, DOI: 10.1016/j.icarus.2011.03.026. (http://www.sciencedirect.com/science/article/pii/S0019103511001175)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:24236
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:28 Jun 2011 23:16
Last Modified:03 Oct 2019 02:54

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