Proceedings Article | 9 October 2006
KEYWORDS: Radar, Synthetic aperture radar, Scattering, Liquids, Backscatter, Electromagnetism, Methane, Image analysis, Dielectrics, Radiometry
The Cassini spacecraft, launched in 1997, begun the exploration of the Saturnian system in July 2004. 44 flybies
of the Saturn largest moon Titan are planned during the four years of the Cassini mission and 16 are Radar
passes. A Radar, developed jointly by JPL, ASI and Alenia Spazio, is mounted on Cassini. The instrument
operates at 13.8 GHz (Ku band) and has passive (radiometer) and active (scatterometer, altimeter, SAR imaging)
capabilities. Until July 2006, six (Ta, T3, T7, T8, T13, T16) radar planned passes have been accomplished.
The data are processed by the JPL and stored in the Basic Image Data Records (BIDR) files, thus obtaining
SAR images and brightness temperature profiles of a significant fraction of Titan's surface. The Radar Cross
Section, RCS, derived from the SAR imagery, reflects the complex Titan's surface morphology. The data show
RCS variations in excess of 20 dB between the "brightest" and the "darkest" areas. On the basis of brightness,
texture, and morphology eight different surface units were identified by Cassini Radar Science Team (CRST)
scientists. The darkest features are good candidate to be lakes of hydrocarbons. Moreover, periodic structures
("sand dunes") have been observed: in this case the RCS variations can be described in terms of tilt angle
effect, thus modifying the local incidence angle. In this paper, the RCS behaviour of the observed features is
studied in detail by the means of the Integral Equation Method, IEM. The dependence of the backscattering
coefficient on the surface physical properties, composition and roughness of different areas is analyzed resulting
in some possible scenarios for the observed features. Surfaces are modeled as Gaussian stationary processes and
volume scattering is also taken into account, due to the transparency of water ice at radar wavelength. The data
of the IEM model are compared with numerical simulations based on the Kirchhoff approximation with auto
similar surfaces performed as preparatory work in the preliminary stage of the Cassini mission. The RCS data
simulated for some likely scenarios of Titan's surface are well consistent with the real radar data and can help
their interpretation in terms of physical and morphological surface properties.
