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D.B. Campbell (Cornell University/NAIC), G.J. Black (National Radio Astronomy Observatory), L.M. Carter (Cornell University), S.J. Ostro (Jet Propulsion Laboratory)
The Arecibo 12.6 cm radar system was used to obtain echo spectra for Titan in both the OC and SC (opposite and same circular polarization to that transmitted) senses of receive circular polarization in the fall of 2001 on 16 nights selected to give a uniform distribution in longitude. All runs were monostatic with the exception of the one at the sub-earth longitude of 111-deg for which the 100-m Green Bank Telescope was also used to receive the echo. While most of the echo power is contained in a broad diffuse component almost all the OC spectra show a weak specular echo which varies in width and amplitude with sub-earth longitude. Total OC specific backscatter cross section varies from about 0.11 in the longitude range 180 to 310-deg to 0.19 at 90-deg, the longitude of the continental sized near-IR high albedo feature. There is a very strong correlation between the 2 micron full disk albedoes and the radar cross sections indicating that the variations in surface composition and/or structure responsible for the near-IR albedo differences are also responsible for the variations in the radar cross section. The cross sections and circular polarization ratios are very different from those of the icy Galilean satellites but similar to those for the trailing hemisphere of Iapetus. The presence of a weak specular component in most of the OC spectra is indicative of the presence of smooth areas at wavelength scales.
The Arecibo Observatory is operated by Cornell University for the National Science Foundation and with support from NASA. The work was partially supported under grants from NASA to DBC and SJO.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.