Titan Surface Temperatures from Cassini RADAR Radiometry

The Cassini Radar instrument includes a passive microwave radiometer that operates at 13.78 GHz (2.2 cm wavelength). The radiometer is used to observe the thermal emission from Titan's surface at resolutions ranging from 5 - 500 km and at a variety of emission angles and polarizations. Nearly the entire surface has been observed through T30, enabling the construction of a mosaiced global map of the surface brightness temperature at normal incidence and the dataset now permits the separation of various contributing factors (dielectric constant and roughness/subsurface scattering as well as physical temperature). Voyager infrared measurements at 530 cm-1 show contributions of flux from the surface and near-surface atmosphere and suggested a symmetric equator-pole gradient of the of the order of 2-3K. Pure surface temperatures may be expected to show some asymmetry, with the south showing some effects of heat deposition from the long summer. Our data are much less influenced by the atmosphere and probe slightly into the subsurface. We present our preliminary results on the variation of surface temperature with latitude, and with terrain height. Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.