The topography of Ganymede: stereo analysis of Galileo SSI images

Abstract

The Galileo SSI camera acquired high resolution (< 100m/pixel) stereoimages in Galymede's Galileo Regio and Uruk Sulcus during the encounters in June (G1) and September (G2) 1996. The images were taken at similar solar illumination and from camera positions separated enough for good stereo conditions. We performed a photogrammetric analysis of these image data and derived Digital Terrain Models and orthophotos (rectified images). The obtained terrain models cover an area of 22 km x 30 km (Uruk Sulcus) and 63 km x 102 km (Galileo Regio), and have spatial resolutions of 200m/pixel and 300m/pixel, respectively. The resolution is by a factor of three poorer than the resolution of the images, due to limitations of the digital image correlation approach. We used patch sizes (correlation windows) of 15 pixels to cope with strong compression artifacts in the G2-images. Both terrain models have similar characteristic height ranges on the order of 1 km. Heights are relative heights becuase ground control information was not available. The Uruk Sulcus terrain shows distinct large-scale grooves and ridges aligned with visible dark and bright surface lineaments. This strong correlation of elevation with material brightness may hold information on the processes that have formed this terrain type and needs to be further explored.