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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
  
  
  
  
Fig. 5: Left: Terrain Model derived from HRSC-images (nadir, forward, and backward) acquired during orbit 18. Heights in 
this model span a range of approx. 3 km and are represented by image brightness. Right: Topographic profiles pl, p2, p3, and 
p4 extracted from this model and from a corresponding MOLA gridded terrain model. 
6. PERFORMANCE OF SRC 
The SRC camera with its large focal length (Table 1) is 
intended to provide high resolution detail within the 
context of the large HRSC scenes. We selected SRC images 
from orbit 37 and orbit 68 for analysis (Figs. 6, 7). Both, 
SRC images and HRSC context images were reprojected to a 
reference HRSC terrain model. The SRC images were 
mosaicked using the nominal time tag, orbit, and spacecraft 
pointing data. The SRC images fit nicely into the predicted 
location within the HRSC context. Only minor offsets in the 
across-track direction of < 100 SRC pixels are observed 
(presumably due to offsets from the nominal co-alignment 
between the cameras), which require small shifting to make 
the SRC and HRSC images precisely fit. (However, some few 
SRC images suffer from large time-tag errors which place the 
SRC images into completely erroneous locations of the 
HRSC context.) 
Using a digital image matcher as a tool for position 
measurement of features in the images, we made a rough 
estimate that the magnification factor of SRC with respect to 
HRSC is 4.33, corresponding to an effective focal length of 
974.5 mm. This value is in good agreement with the 
nominal focal length (Table 1), but it is 1.5% lower than the 
value that has been directly measured on the ground. The 
SRC position (position of the upper left corner of the SRC 
image) within the HRSC scene is re-estimated to be at pixel # 
2694.0. The effective image resolution improvement over 
HRSC (see Fig. 5b), estimated to be approx. a factor of 2, 
remains below the expectations judging from the images 
that have been examined. The quality of the SRC images 
appears to vary from orbit to orbit or even within orbits, an 
effect, which is currently being studied.