The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
further refinements in subsequent processing iterations. 
In general, for DTM derivations all five panchromatic channels 
are used, because this has been shown to produce better results 
over only using the nadir and stereo channels (see Heipke et al. 
2007), therefore the matching scale for the least-squares 
area-based matching was set to the photometry channel 
resolution. 
Iterative low pass image filtering (Gauss and mean filtering) is 
applied in order to improve the image matching process by 
increasing the amount and quality of object points and in order 
to reduce possible misdetections caused by imagecompression 
artefacts and noise. Depending on the results (object point 
distribution and the intersection of the object points) after each 
iteration, selective sub-areas are newly filtered. 
For all our calculations we have only used objects points 
defined by at least triple intersections. In order to eliminate 
blunders a threshold value (depending on the intersection of the 
object points) for the intersection accuracy is set. 
The DTM grid size depends on the object point distribution, 
point accuracy, matching resolution and exterior orientation 
accuracy. For the investigated area two DTMs were generated: 
first, a DTM-raster by interpolation and filtering of multiple 
object points, and secondly, a DTM-raster without interpolation 
and filtering. If more than one object point is in the raster-grid, 
the mean value is calculated. In the next step, all gaps in the 
DTM without interpolation are filled with values from the 
interpolated DTM. After this, box filtering is employed to 
reduce possible artefacts and blunder. 
As an additional DTM quality control we calculated elevation 
differences to the MOLA DTM (see Fig. 3, Fig. 5 and Fig. 7) 
and generated shaded relief DTMs for a visual control (Fig. 8, 
Fig. 9 and Fig. 10) 
4.1 Nominal exterior orientation 
The mean displacement in planimetry for all six orbit strips is 
269 m. Two overlapping areas show high differences in 
planimetry (see Fig. 2): Compared with previous results of other 
orbits; the difference in planimetry of the other three 
overlapping areas is small. The mean height difference between 
HRSC object points and the MOLA DTM is 23 m, but they are 
irregularly distributed over the whole area (see Fig. 3). 
4. RESULTS 
In this chapter, the results of the bundle adjustment and the 
DTM derivation will be discussed for three cases. Fig. 2, Fig. 4 
and Fig. 6 shows the mean displacement in planimetry of object 
points between neighbouring strips using nominal exterior 
orientation, adjustment as a single strip and adjustment as a 
block. Annotation: The arrow scale in Fig. 2 is 200 m and in Fig. 
4 and Fig. 6 50 m. 
4.2 Adjustment as single strip 
The mean displacement in planimetry for all six orbit strips is 
39 m (see Fig. 4). The height differences in the two overlapping 
areas are smaller compared with the nominal exterior 
orientation. Furthermore, the mean height difference between 
the HRSC object points and the MOLA DTM is 5 m and thus 
smaller too (see Fig. 5). In principle, there are no systematic 
variations between the HRSC DTM and the MOLA DTM. The 
reason for the differences are on the one hand, that the 
resolution of the MOLA DTM lower is than the accuracy of the 
HRSC points and on the other hand that the higher-resolution 
HRSC-based DTM, as well as the lower-resolution MOLA 
DTM, includes areas without any object point information. In 
these areas elevation differences are relatively large. 
Figure 2. Results before adjustment (planimetry) 
Figure 3. Results before adjustment (height diff.) 
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