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NASA Science Highlight: Planetary Program Support
Research by K. L. Mitchell1, B. W. Stiles1, C. Veeramachaneni1, A. Hayes2, R. L. Kirk3, J. Andrews-Hanna4, R. D. Lorenz5, E. R. Stofan6, 1California Institute of Technology Jet Propulsion Laboratory;2Caltech; 3USGS Flagstaff; 4Colorado School of Mines, 5Johns Hopkins University Applied Physics Lab., 6Proxemy Research, Inc.
Science Writer, Samantha Harvey
By comparing the calibration of various overlapping Titan RADAR imagery, scientists on the Cassini RADAR instrument team were able to test a new model which is better able to estimate surface heights, elevations and subsurface phenomena within Titan's Arctic lake district. Because of the RADAR instrument's multi-beam nature, they were able to use the "SAR Monopulse Amplitude Comparison Method", which utilized the entire Arctic SARTopo database, derived from RADAR scenes of Cassini's Titan flybys T16, 18, 19, 25, 28, 29 and 30. The result has been the development of the "SARTopo" product which supplements the scant altimetry coverage of Titan with data that are conveniently located with SAR footprints.
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Results: Upon reviewing the data used in this method, Titan lakes and seas appear not to exist on a simple equipotential surface, but the elevation distribution does appear to follow the level of the surrounding terrain, which is sloped down toward the main seas. Lakes and surrounding terrain tend to exhibit greater elevations in the western hemisphere (0-180 W) than in the eastern (180 - 360 W). Higher elevations correlate with small, rimmed lakes, and lower elevations with more diffuse seas. All but 3 of 39 lake samples are at elevations below that of their surroundings, lending credence to the method. The three exceptions were in SAR-dark expanses of sea, close to the noise floor. There is also a generally good correlation with stereo-derived DTM (in Figure 2, above). Two of the 39 lake samples are unexpectedly low in elevation. Both are internal to large expanses of fluids and so may represent similar non-physical results to those described above.
Implications:
The good correlation of SARTopo intra-lake lows (<100 m) with those in the T25-T28 stereo-derived DTM (Fig. 2; [5]) leads to the tentative conclusion that bathymetric (lake bottom) returns can be seen with this model, which improves understanding of Titan's subsurface phenomena.
Significance to Solar System Exploration:
By comparing the calibration of various overlapping Titan RADAR imagery, scientists can get better data sets, to more accurately measure elevations, subsurface flows and features of Titan.
Last Updated: 22 July 2011
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