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E. Marouf (San Jose State University), R. French (Wellesely College), N. Rappaport, A. Kliore (JPL)
Bistatic-scattering is a well-established technique for determination of the nature and physical properties of planets and their satellites. Cassini offers an unprecedented opportunity to observe quasi-specular bistatic-scattering from an icy satellite, potentially at three coherent wavelengths. Circularly-polarized X-, S-, and Ka-band Radio Science signals transmitted from Cassini are observed at the NASA/DSN ground receiving stations after scattering from Titan's surface. Information regarding surface properties is recovered from analysis of the received echo intensity, polarization, and spectral properties. In particular, echo polarization over the Brewster-angle-range of icy surfaces (50-65 deg.) yields direct estimates of the (composite) surface dielectric constant independent of surface roughness (if surface scattering is dominant). Observations over a range of scattering angles yield additional diagnostic information regarding the nature of the scattering mechanism and related physical surface properties (liquid vs. solid, surface vs. volume, surface roughness, …etc). The relatively low-altitude of many Titan flybys (950 km) yields excellent to good SNR within 15 minutes from closest-approach (C/A), even for surface reflectivity of only a few percent. In addition, the close flybys enhance potential echo detectability at all three wavelengths, yielding a wealth of information regarding dispersive characteristics of the scattering mechanism. More limited X-band-only observations may be achieved at fair SNR within roughly 40 minutes from C/A. The bistatic-scattering observations over a range of quasi-specular scattering angles provide excellent synergy to the backscattering-limited Earth-based-radar as well as Cassini RADAR observations.
Support by the NASA/JPL Cassini Project is acknowledged.
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