FIRST STEREOSCOPIC RADAR IMAGES OF TITAN
R.L.
Kirk1, E. Howington-Kraus1, K.L. Mitchell2, S.
Hensley2, B.W. Stiles2
1 - U.S. Geological Survey, Astrogeology Program, Flagstaff,
Arizona, USA
2 - Jet Propulsion Laboratory, Pasadena, California, USA
rkirk@usgs.gov
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.