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DE- AND RE-SHADING OF MARS EXPRESS HRSC IMAGE DATA FOR 
HOMOGENIZATION OF MAP RELIEF SHADING 
E. Dorrer', H. Mayer', A. Ostrovskiy, S. Reznik', G. Neukum" and the HRSC Co-Investigator Team 
* Institute for Photogrammetry and Cartography, Munich Bundeswehr University, Werner-Heisenberg-W eg 35, 
D-85577 Neubiberg, Germany, egon.dorrer@unibw-muenchen.de 
" (HRSC Principal Investigator), Institute for Earth Sciences, Freie Universitaet Berlin, Malteserstr. 74-100, 
D-12249 Berlin, Germany, gneukum@zedat.fu-berlin.de 
Commission IV, WG IV/9 
KEY WORDS: _ Extra-terrestrial, Planetary, Mars Express HRSC Imagery, Three/Multi-Line Scanner, Simulation, 
DEM/DTM, Software, Experimental 
ABSTRACT: 
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-pho- 
togrammetric 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 in- 
tegrated 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 modi- 
fying illumination induced shades in image scenes of the Martian surface. Kernel is an SFS method known from Computer Visualiz 
ation. 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 de 
scribed 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. 
1. INTRODUCTION processing, i.e. mainly radiometric calibration, at the DLR in- 
stitute began immediately, followed by first attempts of high 
Automatic generation of digital image maps of the Martian level scientific 3D-processing from the three to five HRSC 
surface is a major task of the Photogrammetry and Carto- stereo channels. For the first time spectacular 3D-scenes of 
graphy Group (PCG) of the Mars Express HRSC Co-Investi- the Martian surface of medium to high resolution stereo im- 
gator Science Team. HRSC (High Resolution Stereo Scanner agery in color as well as instructive perspective views could 
Camera) is one of seven scientific instruments on the Mars be presented to the general community. 
Express Orbiter, all for the purpose of gathering data for geo- 
logical, mineralogical, atmospheric, gravitational, and carto- In our studies emphasis has been placed from the very begin- 
graphic studies over a period of two years. Guided by the In- ning to complement photogrammetric image matching based 
stitute of Planetary Research of the German Aerospace Cen- object reconstruction by a Shape-from-Shading (SFS) ap- 
ter (DLR), science work within PCG — one of four HRSC proach. The principle of SFS was introduced and defined 
groups — is carried out by eight institutions. Within the sci- thirty years ago by B.K.P. Horn, the “father of SFS" (Horn, 
ence data processing program the group's main task is the de- 1970). On Mars one of the prerequisites of SFS, viz. texture- 
velopment of software for generating high quality cartograph- less surface, is largely fulfilled. Exactly on this type of sur- 
ic and GIS products such as ortho-image maps of the surface face, photogrammetric "Shape-from-Matching" (SFM) fails, 
of Mars. These products form the basis for further data deriv- therefore the two very different methods complement each 
ates for a variety of science disciplines. other. In fact, SFS, as kernel of a novel process denoted De- 
Re-Shading (DRS), is capable of a substantial refinement of 
Having been set-off by a Russian Soyuz/Fregat launcher from the Digital Elevation Model (DEM) obtained by stereo pho- 
Baikonur spaceport in Kasakhstan on 2 June 2003, the Mars togrammetry alone. Similar findings have already been dis- 
Express space craft reached Mars on 27 December 2003 and, cussed by several authors, e.g. (Dorrer, et.al., 1998), ( Hashe- 
after ejection of the — later failing — Beagle 2 lander, started mi, et.al., 2002), (Rajabi, et.al., 2003), yet never have been 
manoeuvring into a highly elliptical capture orbit from which applied under real conditions and on a bigger scale. This will 
it was transferred into its final operational near polar orbit. be the case for the first time with Mars Express cartography. 
Orbiter science operations with systematic data transmission By exploiting additional information beyond primary HRSC 
down to Earth began in mid January 2004. During the fol image data, SFS for the first time will enable a distinct refine- 
lowing few months a tremendous amount of image data at ment of the DEM generated by photogrammetric matching. 
different resolutions and on different spectral channels were Despite the still preliminary and simplified approach to the 
down-linked via the Deep Space Network. Low level data 
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