|
In this paper, the Titan lake features detected by active and passive sensors during the Cassini flybys have been
analyzed. The first part of the work is dedicated to the analysis of the SAR data. The main aim of this part is
to find situations where it could be feasible to infer information about the likely ranges of lake parameters. The
approach is mainly divided in the following steps:
• Electromagnetic modeling of the lakes surface and comparison with measured radar data;
• Introduction of the electromagnetic modeling in the inversion procedure based on a Bayesian framework.
The inversion procedure itself is divided into training and test phase.
• Analysis of the inferred information and determination of the likely ranges for lake optical thickness and
wind speed.
In the second part, the analysis have been extended to the radiometer data.
The likely ranges of surface parameters e.g. dielectric constant, wind speed and optical thickness derived from
the Bayesian inversion have been used as an input to a forward radiative transfer model calculation to obtain
simulated brightness temperatures. Comparison of the observed and computed brightness temperatures will
allow us to address the consistency of the observations from the two instruments and to determine the coarse
characteristics of the surface parameters that lead to consistent results between the two instruments at a global
scale.
In processing radiometric data two main aspects have to be considered. The correlation between SAR and
radiometry is limited by the low radiometry footprint resolution at closest approach, preventing detection and
correlation of surface features smaller than 6 km azimuth resolution. In addition, there is a large-scale variability
in calibration among the five radiometer beams caused by sidelobes that should be accounted for obtaining
relative brightness variations. For these two reasons, the data have been compared only on areas with large
extensions such as large liquid surfaces detected during T25 and T30 Cassini flybys and relative surrounding
areas. Furthermore only relative brightness temperature, calculated as difference between various areas, have
been considered.
|
