Titan's Lake Distribution and Classification from the Cassini RADAR

Details Titan's Lake Distribution and Classification from the Cassini RADAR Titan's Lake Distribution and Classification from the Cassini RADAR

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p23b1350a&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #P23B-1350

Mathematics

Logic

1800 Hydrology, 6281 Titan

Scientific paper

A picture is emerging of surface hydrology in the north polar region of Titan. Quasi-circular, lobate to complex features, which take up 2.4% of the global coverage area (22.4% of the surface), are separated into 3 classes: dark lakes, granular lakes, and bright lakes. Dark lakes are interpreted as liquid filled while bright lakes are interpreted to be empty basins. Based on observed backscatter and geospatial position, granular lakes are inferred as transitional between dark and bright counterparts. In this work, the differences in distribution, morphology, and radiometric properties between the classes are explored using the Cassini Radar. The differences and similarities between the classes have implications for the interaction and evolution of hydrologic features on Titan. Dark lakes, which represent 84% of the mapped features, are found between 65°N and 90°N, and show a general trend of decreased off-nadir backscatter poleward. Granular lakes, which are distinguished from dark lakes by a higher backscatter cross-section relative to their surroundings, are found as low as 55°N and extend to 77°N. We have found no abrupt statistical change between dark and granular lakes, suggesting a smooth transition between the two classifications. Bright lakes, distinguished by their higher backscatter relative to their surroundings, represent ~10% of observed lakes. They are found in the same latitude range as granular lakes, often interspersed among them. Shoreline complexity, expressed as the fractal dimension, shows that bright and granular lakes are characteristically more circular than dark lakes. High resolution (~5 km) altimetry collected coincident with Synthetic Aperture Radar (SAR) images shows that bright lakes are empty basins 250-350 m in depth. Comparison between SAR images and integrated power in the altimetry waveforms shows that bright lakes have high return in both nadir and off-nadir backscatter relative to their surroundings. This allows distinguishing variations in roughness from intrinsic properties of the materials. Initial topographic measurements from stereo radar images constrain the relative elevations of nearby lakes, allowing comparison among lake classes. In cases where filled lakes lie above empty lakes, a state of disequilibrium with respect to subsurface transport is implied. In general, a single topographic contour cannot be used to separate empty and full lake positions. Combining morphology, radiometry, and topography provide complementary information on the nature of Titan's surface and sub-surface hydrocarbon hydrology.

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