Models of synthetic aperture radar backscattering for bright flows and dark spots on Titan
Résumé
The synthetic aperture radar (SAR) imaging mode of the Cassini RADAR instrument enables us to map the surface of Titan through its thick atmosphere. The first Cassini close flyby, acquired on 26 October 2004, revealed a complex surface, with areas of low relief and dome-like volcanic constructs, flows, and sinuous channels. In particular, fan-like features with strong radar backscattering were observed. Such structures, extending from tens of kilometers to more than 200 km in length, could be the result of cryovolcanism. Several radar dark spots, up to 30 km across, were also observed; they may correspond to smooth hydrocarbon deposits. We present here a first modeling of these radar-bright and radar-dark features on the basis of classical radar backscattering models. We considered two main materials which could constitute the surface of Titan, tholins and water-ammonia ice, and modeled both single- and two-layer cases, taking into account volume and subsurface scattering. Our results show that SAR-bright regions could better be explained by the effect of a thin layer of water-ammonia ice covering a tholin substratum. Radar-dark spots can be modeled in two ways: a rough tholin surface or a smooth one with some volume scattering. We show that multi-incidence SAR data could help discriminate between the various scenarios proposed.
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