Toward comprehensive Titan digital topography construction: A technical demonstration with stereogrammetry and photo/radarclinometry
Abstract:Topographic reconstruction is a high priority task for the solid planet and satellite exploration missions. Laser/radar altimetry and stereo analyses have been widely used for this purpose and achieve high quality 3D topographic data over various planetary surfaces such as Venus, Mercury, Moon and Mars. However, in contrast with inner planet and satellite, the base data sets to compose digital topography over outer planets and satellites are very limited.
Titan, the largest satellite of Saturn has also too limited data inventory to achieve sufficient spatial resolution in topographic data, in spite of increasing interests about the detailed topography owing to the recent interesting discoveries on methane fluvial system, aeolian geomorphologies and possible tectonic activity.
Therefore the endeavours to increase the coverage of digital topography employing radargrammetry (Kirk et al. 2009), radar altimetry (Elachi, et al. 2005) and SARtopo (Stiles et al. 2009) have been actively conducted. Although these efforts result in the construction of a global topographic map, the consequent spatial resolutions of global topography are still poor (Lorentz et al. 2013).
In this study, we tried to improve the coverage and the quality of Titan digital terrain model employing approaches as follows; 1) A semi-automated stereo matching scheme manipulating low signal-to-noise SAR image pair incorporating adaptive filtering and base topography, 2) the geodetic control improvement of stereo SAR pair based on altimetric measurements, 3) introduction of radarclinometry to refine the topography from stereo analyses. Especially together with the technical improvements to exploit SAR stereo pair, the possibility to mine height information from Visual Infrared Mapping Spectrometer (VIMS) was actively explored by the means of hybrid stereogrammetry between VIMS and SAR image pairs and photoclinometry. The developed scheme was applied for a few testing areas especially over Xanadu which is the largest topographic feature over Titan and well covered by SAR and VIMS. The constructed topography revealed many interesting geomorphic features such as drainage networks and rugged terrains in detail. To fully demonstrate the potential of these approaches, technical details will be continuously improved.