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S.G. Gibbard, B. Macintosh, C.E. Max, D. Gavel (LLNL), I. de Pater, H. Roe (U of C, Berkeley), E.F. Young (Southwest Research Institute), C.P. McKay (NASA Ames)
We will present results of observations of Titan made in 1996-1998 using speckle imaging at the 10-m W.M. Keck Telescope. Speckle imaging allows a resolution of 0.04 arcseconds at 2 microns, or 20 resolution elements across the disk of Titan. Our observations at K, H, and J bands now extend to Titan's darker trailing hemisphere. Using a radiative transfer model incorporating fractal haze properties, we are able to separate the contributions of Titan's atmosphere and surface, and thus to both determine the optical depth of Titan's haze layer and to construct surface albedo maps. We find that Titan's trailing hemisphere is overall very dark, with a surface reflectance <0.05, consistent with the presence of solid or liquid hydrocarbons or perhaps very large-grained ice. The leading hemisphere is brighter, but with dark patches of very low albedo similar to the trailing hemisphere. We also find that Titan's haze optical depth has changed from 1996 to 1998, showing an increase in optical depth in the northern hemisphere and a decrease in the southern hemisphere, as predicted by seasonal models of Titan's haze variation.