Hayes, A. G. and Wolf, A. S. and Aharonson, O. and Zebker, H. and Lorenz, R. and Kirk, R. L. and Paillou, P. and Lunine, J. and Wye, L. and Callahan, P. and Wall, S. and Elachi, C. (2010) Bathymetry and absorptivity of Titan's Ontario Lacus. Journal of Geophysical Research E, 115 (E9). Art. No. E09009. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20101026-144947994
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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 (κ). The derived value, κ = (6.1_(−1.3)^(+1.7)) × 10^(−4), corresponds to a loss tangent of tan Δ = (9.2_(−2.0)^(+2.5)) × 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 Information:||© 2010 American Geophysical Union. Received 8 December 2009; accepted 3 June 2010; published 23 September 2010. The authors would like to thank Bryan Stiles for helpful discussions and the Cassini engineering team, without whom the data presented here would not have been possible. This work was supported by the Cassini Project, managed by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA as well as by NASA’s Graduate Student Researchers Program and the NSF Graduate Research Fellowship Program.|
|Subject Keywords:||Titan; lakes; radar|
|Official Citation:||Hayes, A. G., et al. (2010), Bathymetry and absorptivity of Titan's Ontario Lacus, J. Geophys. Res., 115, E09009, doi:10.1029/2009JE003557.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||19 Nov 2010 23:29|
|Last Modified:||26 Dec 2012 12:33|
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