International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004 
  
  
  
  
  
  
Inter 
2. MODEL CONSTRUCTION 
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2.1 Panoramic Images surfa 
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All terrestrial photography was recorded with an Olympus ae 
Camedia C-1400L digital camera. The size of a single record thick 
is 1280 x 1024 pixels. The wide end of the zoom optics was Drew 
used, corresponding to a focal length of 1400 pixels. The and] 
camera has been calibrated and lens distortions of images diffe 
have been corrected. ; ; : foll 
Figure 3. DEM of Engabreen test area in 2002 
Panoramic images have to remain concentric while rotating jon 
the ‘camera in order to preserve the central projection. The 2,4 Densification of Smaller Scale DEMs 
concentricity is controlled with a cross slide on the camera : —-— 
stand. In this study panoramic sequences consisted of three Close-range DEMS san aise be used io density airhoms There 
images with an overlap of approximately 30 %. This DEMs. The points of a sparse model can be projected to a by th 
corresponds to an approximate angle of view of 120° (Figure terrestrial stereo model in order to visualize differences or to measi 
1). In plane projection a panoramic image with a wider angle estimate ihe accuracy of the gir bome DEM. The teretrial Case 
of view than 180° grows infinitively large. The images were DEM of Hintereisferner test area in 2002 is presented in centre 
combined using two dimensional projective transformation. Figure 1 and Dart ‚of an airborne laser Scanner model comer 
The algorithm has been presented by Póntinen, 2000. projected on it in Figure 5. Stereo viewing shows that the often 
models don't match correctly, but it also shows that there are 
some false points in the laser data. The ii 
case ; 
photo: 
match 
Engab 
solid 1 
Figure 1. A panoramic image combined from a sequence of orient: 
three images. contro 
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2.2 Orientations Figure 4. The terrestrial DEM of Hintereisferner test field in should 
September 2002. out as 
The orientations of panoramic images were calculated using carry « 
Intergraphs Z/I digital workstation software. The geometry of of the | 
ground control points complicated the absolute orientations 
of the Engabreen stereo models. The control points were | 3.1 Re 
located in front of the view, causing errors to the more distant 
areas of the models. In the year 2002, one control point was The ac 
measured on the glacier surface. As expected, that improved geomet 
the results. Figure 5. The laser DEM of the Hintereisferner test field of an* 
: 3 : ; (processed by Olli Jokinen) from the same day as the | of the« 
On Hintereisferner the control points were located on ice. terretrial DEM. | distorte 
The geometry of the control is good but there is a possibility | residua 
that the control points had moved between the photography 2.5 Glaciological Change Detection | panorai 
and the tacheometer measurements, because it was not | the pix« 
possible to record the photography simultaneously with On the Engabreen study area the glacier surface is highly | when re 
tacheometer measurements. crevassed as the glacier tongue is flowing down on a steep | Imagin; 
slope. Quite a lot of melt water is available, but the melt pixels. 
paralla» 
2.3 Digital Elevation Models 
The digital elevation models were digitised from the 
absolutely oriented stereo models using Intergraphs Z/I 
software. In Engabreen DEMs (Figures 2 and 3) the point 
density is 20 cm while it is 50 cm in Hintereisferner DEMs. 
  
Figure 2. DEM of Engabreen test area in 2001 
water channels do not form a stable network because of the 
rapid ice movement. Despite that the effects of the melt water 
can be significant target in DEMs. There are almost no 
supraglacial debris at all. Occasionally some ablation hollows 
occur surrounded with a very thin dirt layer. As the hollows 
are more exposed to the sun on one side than another their 
location tend to change. The movement can be as much as a 
few centimetres in one day requiring an extensive study 
period. (Ferguson 1992: 36-38, Betterton 2001). 
On Hintereisferner there are lots of debris on the glacier 
surface close to the glacier sides and snout. The supraglacial 
debris absorbs more sunlight than clean ice, which affects 
strongly to the melting of the ice. A thin debris layer (less 
than a few cm) will transfer the heat to the ice beneath and 
increase melting. On the other hand a thicker layer will 
insulate the ice and reduce melting. Large stones and 
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