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2 - INTERFEROMETRY RAW PRODUCTS 
The two single look complex images of an interferometric pair are firstly co-registered. Then we elaborate three 
images : an amplitude image, a coherence image and a phase image (or fringe pattern). 
We call standard interferometry raw product the set of those three images. Those images share the same 
geometry. 
2.1. Amplitude image 
This image is a conventional image of radiometry. It is given to help for locating points of interest on the two 
other images. Image 10 shows the amplitude image of the 23 September 1991 scene which geometry has been 
used as reference for the two interferometric pairs. 
2.2. Coherence image 
The measure of the coherence brings qualitative information about the stability in time of the ground (images 5 
and 7). 
Thus, the coherence provides qualitative information on ice motion. A good coherence at the ice surface 
corresponds to the near constant state of the surface and low ice motion. A lack of coherence (dark region of the 
image) corresponds to a change of the state of the surface and/or to fast glacial flow. 
2.3. Raw fringe pattern 
The fringe patterns (images 4 and 6) contain information on orbital satellite position, ground topography and 
motion of the glaciers. Gear fringes correspond to stable surface state and are associated to high coherence. 
The effect due to orbital satellite position and ground topography can be removed using a DEM to 
highlight the motion of the glacier towards the satellite. This is done by differential interferometry. 
3 - DIFFERENTIAL INTERFEROMETRY 
3.1. Use of a Digital Elevation Model 
A conventional Digital Elevation Model was not available on the Spitsberg but only elevation contour lines 
extracted from a map (image 8). We therefore had to derive the elevation map from the elevation contour lines 
(image 9). 
This elevation model has been used with the orbital data of the tracks to simulate a SAR image (image 
11). By correlation with the actual SAR image of 23 September 1991 (image 10), the orbital positions could be 
locked to a geographic reference. 
The elevation model has then been used again, but with the locked orbital positions, to compute the 
fringe pattern caused by orbital trajectories as well as elevation (image 12) in the interferometric pair of 17 
September 1991 with 23 September 1991. 
3.2. Differential fringe pattern 
The fringe pattern caused by orbital trajectories and elevation (image 12) has been removed from the raw fringe 
pattern (image 7), to produce the differential fringe pattern (image 13). Image 14 is the same image, but the 
regions of low coherence have been masked. 
The differential fringe pattern is caused by glacier moves (and errors in the elevation model used) and 
measures only the component of the displacement of the icy surface toward the satellite. The precision of the 
results will depend highly on the direction of the flows. 
Image 1 • 
September 
@ESA/ER 
4 - CONCLUSION 
This work on the ice flows in glaciers of western Spitsberg is not finished. For instance, the elevation model 
used is too unprecise and its derivation from the elevation contour lines has to be improved. 
However, those preliminary results show that differential interferometry did to allow a monitoring of the 
ice flow in several glaciers during the time elapsed between data takes.