First stereoscopic radar images of Titan

Saturn's giant, cloud-covered satellite Titan, larger than the planet Mercury, is the last major piece of unexplored  real estate in the Solar system.  The NASA/ESA Cassini spacecraft carries a variety of instruments that are being used to map the surface of Titan, including optical instruments that provide a global synoptic view and spectroscopic information, and microwave imager (Cassini Titan RADAR) that can produce a 5000-km long 300-1400 m resolution image that covers ~1% of Titan during a flyby encounter with the satellite.  The first 7 such images, obtained between October 2004 and July 2006, covered nonoverlapping areas and revealed a diverse (and surprisingly Earth-like, despite the very cold temperature and different chemistry of the surface) set of geologic features, including volcanos, dune fields, channels, mountains, and impact craters.  Beginning with the T18 encounter in September 2006, all but one of the dozen RADAR images obtained during the remainder of Cassini's prime mission will overlap with previous coverage.  The repeat coverage has numerous cartographic and scientific applications, including serving as the basis for the most accurate geodetic control network of Titan, providing information about the surface materials as revealed by their angle-dependent microwave-scattering properties, allowing comparisons to look for temporal changes, and providing information about surface relief that can be exploited by radar-stereogrammetric mapping.  We report the initial results of automated and manual stereo elevation measrurements at the USGS and JPL.  These reveal local relief of several hundred to a thousand meters, associated with a canyon system and probable lakes in the northern hemisphere, a result that is consistent with the available topographic information about other parts of Titan from altimetry and radar shape-from-shading.  Work is underway to develop more rigorous and efficient stereomapping tools at both institutions, based on those originally designed for the Magellan radar imagery of Venus, and to apply these to the extended stereo coverage that will become available over the next few years.