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Bathymetry and absorbitivity of Titan's Ontario Lacus

Journal of Geophysical Research

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Abstract

Ontario Lacus is the largest and best characterized lake in Titan's south polar region. In June and July 2009, the Cassini RADAR acquired its first Synthetic Aperture Radar (SAR) images of the area. Together with closest approach altimetry acquired in December 2008, these observations provide a unique opportunity to study the lake's nearshore bathymetry and complex refractive properties. Average radar backscatter is observed to decrease exponentially with distance from the local shoreline. This behavior is consistent with attenuation through a deepening layer of liquid and, if local topography is known, can be used to derive absorptive dielectric properties. Accordingly, we estimate nearshore topography from a radar altimetry profile that intersects the shoreline on the East and West sides of the lake. We then analyze SAR backscatter in these regions to determine the imaginary component of the liquid's complex index of refraction (Kappa). The derived value, Kappa = (6.1-1.3+1.7) x 10-4, corresponds to a loss tangent of tan Delta = (9.2-2.0+2.5) x 10-4 and is consistent with a composition dominated by liquid hydrocarbons. This value can be used to test compositional models once the microwave optical properties of candidate materials have been measured. In areas that do not intersect altimetry profiles, relative slopes can be calculated assuming the index of refraction is constant throughout the liquid. Accordingly, we construct a coarse bathymetry map for the nearshore region by measuring bathymetric slopes for eleven additional areas around the lake. These slopes vary by a factor of ~5 and correlate well with observed shoreline morphologies.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Bathymetry and absorbitivity of Titan's Ontario Lacus
Series title:
Journal of Geophysical Research
Volume
115
Year Published:
2010
Language:
English
Publisher:
American Geophysical Union
Contributing office(s):
Astrogeology Science Center
Description:
11 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Geophysical Research
First page:
E09009