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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXX V, Part B7. Istanbul 2004 
boulders are also protecting the ice from melting. These so 
called glacier tables can finally be well above -the glacier 
surface supported by an ice pile. Dirty cones and ridges are 
features consisting mostly of ice but are covered with a debris 
layer. Their development depends on the particle size and 
thickness as well as the slope angle. (Ostrem 1959: 228, 
Drewry 1972, Kajuutti 1989, Kirkbride 1995: 289-291, Benn 
and Evans 1998: 228-230, Betterton 2001). The change of 
different debris covered features is a suitable target to be 
followed with close-up photography. 
3. RESULTS AND DISCUSSION 
The orientations of terrestrial stereo image pairs are affected 
by the weaknesses in quality of images, in the accuracy of 
measurements, and in the quality of ground control. In the 
case of panoramic images also poor stability of projection 
centre during photography distorts DEMs. Therefore the 
camera must be set up very carefully as the glacial terrain is 
often rough and unstable. 
The importance of reliable ground control is emphasized in 
case an object is moving during the series of repeated 
photography. The DEMs of successive years have to be 
matched for the comparison and change detection. On 
Engabreen the possibility to measure the ground control to a 
solid rock has most likely improved the results of absolute 
orientation. On the other hand on Hintereisferner the net of 
control points has been regular as it was possible to measure 
it on the glacier itself. For a better matching the DEMs 
should be wider covering some solid land, which could work 
out as a reference. On Engabreen this would be fairly easy to 
carry out. On Hintereisferner it is almost impossible because 
of the loose sediments around the glacier tongue. 
3.1 Relative Orientation 
The accuracy of relative orientation depends highly on the 
geometry of panoramic images. In case the projection centre 
of an image sequence has not been stationary, the geometry 
of the central image is still correct but the adjacent images are 
distorted. This will show up in relative orientation as grown 
residuals of points of that area. In normal case the whole 
panoramic image cannot be used for DEM measurements as 
the pixels near both ends of a panoramic image tend to stretch 
when rectified to a plane. Standard errors of unit weights (Z/I 
Imaging, 2001) of stereo models vary between 0.3 to 0.8 
pixels. It corresponds to 9.6 to 25 pm. Table 1 shows the y- 
parallaxes of one panoramic stereo model. 
771 
Engabreen 2002 
Pt ID PY(px) Arc seconds (") 
101 0.19 28.07 
102 0.01 1.46 
103 0.07 11.70 
104 0.21 33.95 
105 0.11 17.54 
01 0.01 1.79 
10 0.06 8.93 
11 0.56 91.46 
12 0.44 71.97 
106 0.59 95.85 
107 0.83 135.48 
108 0.21 33.30 
109 0.06 9,75 
Table 1. An example of results of relative orientation. Y- 
parallaxes after orientation are expressed in pixel and arc 
second units. Standard error of unit weight is 0.33 px 
(53.03"). 
3.2 Absolute and Exterior Orientation 
The accuracy of absolute orientation depends mainly on the 
accuracy of ground control and the accuracy of the relative 
orientation. If the relative orientation is affected by a 
displacement(s) of the projection centre during the 
photography of an image sequence, the absolute orientation 
will also be corrupted. Tables 2 and 3 show the results of 
absolute and exterior orientation and the differences to 
measured coordinates of projection centres of two panoramic 
stereo pairs. The results show that exterior orientation gives 
better solution in this case.