Imaging of Phobos by the HRSC on Mars-Express

From August through November 2004, Mars Express had several encounters, as close as 150 km, with Phobos. During these flybys, the High-Resolution Stereo Camera (HRSC) on board obtained images of this Martian satellite (13x11x9 km) in stereo and color, showing detail down to 6 m resoltion. Utilizing the stereo images and methods of photogrammetry we derived a digital elevation model covering approx. 1/4 of the satellite's surface. This terrain model allowed us to perform detailed morphological and spectro-photometric studies. The high geometricalprecision of the imaging experiment also permitted us to improve the orbit of Phobos. Using ground control points we found that the satellite has advanced by ~6 sec. (corresponding to 12 km along the orbit) beyond what is predicted by the ephemeris from the Viking era