Analysis of Cassini altimetric crossovers at Titan

Over the course of its mission, Cassini flew multiple times over Titan’s surface collecting altimetric data with its radar. We analyzed altimetric measurements collected by Cassini’s radar when flying on the same region as to correlate such measurements (i.e., a crossover) and look for differences in altimetry caused by either inaccuracies in the altimetric measurement, orbital reconstruction errors, or, more interestingly, the time-variable Titan’s shape. Indeed, in a crossover, the observed altimetry is expected to be the same, if not for a tidal signal. This allows us to test both the accuracy of the altimetric measurements and that of the orbital reconstruction. In addition, if the crossover measurements are accurate enough and the geometry is appropriate, it would in principle possible to determine the Love number h2, which describe the response of Titan’s exterior shape to the forcing impressed by Saturn. We identified a total of 11 pair of Cassini’s tracks over Titan in which we have an overlap of the radar footprints from different flybys. We report on our findings for Cassini altimetric crossovers at Titan. We tested the accuracy of altimetric data generated with different processing techniques: the first moment of the returned waveform, the threshold estimator, and the Maximum likelihood Estimator (MLE). The first two techniques can also be corrected for off-pointing angles. Preliminary results shows that the corrected threshold and corrected first moment estimators have the smallest root-mean-square (RMS) value at crossover points. In addition, fitting for a tidal h2 does not significantly improve the RMS, since the tidal signal expected from a fluid body is small when compared to the radar accuracy at the crossover.