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ASSESSMENT OF ICE FLOWS IN GLACIERS OF WESTERN 
SPITSBERG USING DIFFERENTIAL INTERFEROMETRY 
M. ROSSI 
Division Qualité et Traitement de l'Imagerie Spatiale 
Centre National d'Etudes Spatiales 
18 avenue E. Belin 
31055 Toulouse cedex 
ABSTRACT 
Radar interferometry is a powerful tool which allows the computation of Digital Elevation Models and, as a 
second order effect, small surface moves of the centimetre range. This technique has been applied to ERS1 data 
acquired over western Spitsberg during the summer 1991 and the beginning of fall 1991. Most of the scenes 
acquired in summer cannot be combined into interferometric pairs because the surface of the glaciers is very dark. 
However, scenes acquired later during the summer/fall transition show a good reflectivity of the icy surfaces, 
allowing good signal to noise ratio over the glaciers. Among the 12 scenes acquired in this period and processed 
at CNES, 6 have been especially studied for their good coverage and 3 show the right combination of orbital 
parameters, leading to good interferometric fringe patterns. The measure of the coherence brings qualitative 
information about the nature of the moves and may be used as a detection of particularly rapid or particularly 
tormented flows. A digital elevation model has been used to lock the orbital positions to a geographic reference 
and to remove the fringes caused by orbital trajectories as well as the ones caused by elevation. The residual 
fringes allow a monitoring of the ice flow in several glaciers during the time elapsed between data takes. The 
technique does not require ground information пен - specific hardware. 
KEY WORDS : SAR, interferometry, ice flows in glacier 
1 ■ INTRODUCTION 
1.1. Background 
Radar interferometry is a powerful tool which takes advantage of the phases of the SAR image complex pixels. 
Those phases can be used to measure the variations of the satellite-ground distances in the images. An 
interferometric combination of two SAR images allows the computation of Digital Elevation Models. If the 
topography is already given by a Digital Elevation Model, surface moves of the centimetre range can be detected. 
CNES initiated in 1985 a research program on small move detection using SAR interferometry and 
came out in 1993 with the spectacular measure of the displacement field of an earthquake 1 . 
This technique has also been applied to ERSI data acquired over western Spitsberg during the summer 
1991 and the beginning of fall 1991 (12 scenes in total) to map the displacement field of the icy surfaces of the 
glaciers. 
1.2. ERS-1 scenes used 
Most of the scenes acquired in summer can not be combined into interferometric pairs : the glaciers are very dark 
on the images because of the presence a water on their surface, witch acts like a mirror. Those scenes have no 
consistent phase information over the glacier but provide nevertheless a useful, more conventional information 
about the physical state of ice surface. 
Some scenes acquired later, during the summer/fall transition, show a good retrodiffusion of the icy 
surfaces. The good signal to noise ratio over the glaciers allows the use of the phase information. 
Among the 12 scenes acquired during this period of time and process«! at CNES, 6 have been especially 
studied for their good coverage and only 3 of them show a right combination of orbital parameters (the satellite 
tracks are not to far), leading to good interferometric fringe patterns. 
Those useful scenes have been acquired the 17 September 1991 with orbit 899 (image 1), the 23 
September 1991 with orbit 985 (image 2) and the 2 October 1991 (image 3). 
The interferometric pairs used in this paper are 17 September 1991 with 23 September 1991 and 23 
September 1991 with 2 October 1991. 
1 Mas sonnet & all. "The displacement field of the Landers earthquake mapped by Radar Interferometry", Nature, 8 
July 1993