De- and Re-shading of Mars Express Hrsc Image Data For

Within the Photogrammetry and Cartography Group (PCG) of the Mars Express HRSC (High Resolution Stereo Scanner Camera) Co-Investigator Science Team, the main task of which is the development and derivation of high quality cartographic and GIS products of the Martian surface, from the very beginning emphasis has been placed on complementing and improving the stereo-photogrammetric DEM by Shape-from-Shading (SFS) methods. This is possible due to the low textured surface of Mars – contrary to Earth. The paper discusses the present state of methodical and experimental research leading to a software prototype that is to be integrated in the general data processing package developed by the guiding Institute of Planetary Research of the German Aerospace Center (DLR). The paper first deals with the description of a novel process denoted De-Re-Shading (DRS) for the purpose of modifying illumination induced shades in image scenes of the Martian surface. Kernel is an SFS method known from Computer Visualization. The SFS-refined DEM will be the basis for subsequent modifications of image shades towards rigorous homogenization and optimization of relief shading in the digital ortho-image maps to be generated by the PCG. From a methodical view point SFS is described as a problem of Variational Analysis with constraints. The Conjugate Gradient method is employed to a direct solution of the extended discrete unconstrained minimization functional. Finally, first preliminary results utilizing appropriate real HRSC image data as well as MOC/MOLA data are presented. Despite certain limitations to the method and the preliminary development stage, the results confirm the considerable refinement potential of SFS for an approximate DEM.