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Case 5: This is the most extreme case possible, using 
only one control point in the first scene. As expected, 
it is then not possible to estimate the orbit radius and 
the yaw angle offset. This is most clearly seen in the 
Y component where there is a trend in the across 
track direction (Figure 7) corresponding to a missing 
yaw estimate of 0.05 degrees. Still, the total rms 
errors are kept close to 1 pixel. 
5. ALTIMETRIC ACCURACY 
5.1 Test area 
A 25km x 25km area corresponding to a topographic 
map sheet 1:50,000 was selected for evaluation of the 
DEM computations. The area is situated in the 
southernmost scene of the strip (scene 6). The terrain 
is varied. Boreal forest with clearcuts dominates to the 
east, low treeless mountains to the west, and a river, 
bordered by agriculture, is running in the middle. The 
height ranges from 300 m to 900 m. The image pair is 
of good quality, except for a small cloud, and cloud 
shadow, near the centre of the map area. The nadir 
looking image over the map area is shown in Figure 8. 
  
Figure 8. Nadir looking image (band 3), showing the 
area covered by the reference DEM. 
5.2 Test strategy 
The JERS-1 stereo model was adjusted by the 
method described in paragraph 3.1. The strategy of 
the test was to set up different configurations of 
control which were successively more difficult and 
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demanding. The numbering of the scenes is from 
north to south, with number 6 being the one 
containing the test map area. The following 
configurations were tested: 
1. Control points only in scene 6. 
2. Control points only in scene 5. 
3. Control points only in scene 4. 
4. Control points only in scene 3. 
4a. 4 control points only in scene 3. 
4b. 3 control points only in scene 3. 
4c. 2 control points only in scene 3. 
4d. 1 control points only in scene 3. 
The last test is most extreme, with only one control 
point available 225 km away from the map area. 
5.3 Altimetric results 
The DEM's were computed using multi-point matching 
(Rosenholm, 1987). The procedure is completely 
automatic, and no post-editing was performed to 
eliminate effects of the cloud. The DEM was 
calculated with 200 m grid distance. The computed 
DEM from test case 1 is shown as a grey-tone image 
in Figure 9. The results were compared to the 
reference DEM from the Swedish Land Survey. 
Statistics in the form of mean and standard deviation 
were calculated for the differences between computed 
and reference DEM. The results are shown in Table 
2. 
  
Figure 9. DEM computed in test case 1. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996