MEASUREMENT OF GLACIER VELOCITY FIELDS USING VERY PRECISE 
MULTITEMPORAL CORRELATION ON HIGH RESOLUTION SPOTS IMAGES 
Héléne Vadon !, Etienne Berthier 2 
! CNES, 18 Avenue Edouard Belin, 31401 Toulouse, France. helene.vadon(@cnes.fr 
? OMP-LEGOS, 18 avenue Edouard Belin, 31401 Toulouse, France. etienne.berthier(a) cnes.fr 
KEY WORDS: SPOT, Glaciology, SPOT, Mapping, Measurement, Correlation, Accuracy, Interferometry 
ABSTRACT: 
Monitoring of ice velocity field is one of the key issues to glacier dynamics understanding. Surface velocity fields can provide useful 
information on phenomena such as glacier surges or ice fall. They can also reflect the effect of global warming on the dynamic of ice 
masses. 
Although the surface displacements of glaciers can be monitored locally with ground GPS points, this solution is difficult in terms of 
both implementation and cost. 
We show how glaciers displacements can be accurately measured using correlation of sequential high resolution optical satellite 
images. The advantages of this technique are first its potential temporal resolution, depending on the re-visit period of the satellite 
system, second its large spatial coverage, and third its resolution, proportional to the image resolution. 
The availability of a very high resolution remote sensing satellite like SPOTS opens the way for such application. Due to its unique 
compromise between a 2.5m resolution and a 60 km swath, this satellite is potentially very useful for accurate measurement of terrain 
displacement, over large areas like glaciers. 
We present the methodology developed to measure glaciers surface displacement by image correlation. An example is shown over 
the French Alps. The paper addresses methodological issues: images co-registration, geo-referencing, glacier distortion measurement, 
velocity field computation. We also discuss coherence issues. This method is finally compared to SAR interferometry. We show 
how, as for SAR interferometry, it can be applied to a wide range of geophysical phenomena, such as earthquakes or landslide. 
RESUME: 
Le suivi des champs de vitesse des glaciers est l'une des clés pour la compréhension de leur dynamique. Les vitesses de surface 
peuvent donner des informations sur les phénomènes tels que les crues glaciaires et les chutes de sérac. Ils peuvent aussi être des 
indicateurs de l’impact du réchauffement global sur la dynamique des masses de glace. 
Bien que les déplacements de surface puissent être mesurés localement en utilisant des balises GPS, cette solution demeure lourde et 
coûteuse. 
Nous montrons ici comment les déplacements peuvent être mesurés finement par corrélation d'images spatiales haute résolution. Les 
avantages de cette technique sont sa résolution temporelle potentielle, qui dépend du temps de revisite du système satellitaire, sa 
grande couverture spatiale, et sa précision, qui est proportionnelle à la résolution des images elles-mêmes. 
La disponibilité d’un satellite de type SPOTS ouvre la voie à de telles applications. Son compromis résolution (2.5m) — fauchée 
(60km) le rend très intéressant pour les mesures de déplacement de terrain sur de larges zones. 
Nous présentons ici la méthodologie développée pour mesurer les déplacements de la surface des glaciers par corrélation d’image. 
Un exemple est présenté sur les Alpes. Le papier détaille la méthodologie employée : co-registration des images, geo-référencement, 
calcul des champs de déplacement. Nous traitons aussi du problème de la cohérence. Finalement, nous comparons cette méthode 
avec l’interférométrie radar. Nous montrons comment, comme pour l’interférométrie, elle peut être appliquée à une grande variété de 
phénomènes géophysiques, tels les déplacements de terrain provoqués par les tremblements de terre ou les glissements de terrain. 
LACE This kind of field campaign is costly and may be difficult. 
1 GLACIER DISPLACEMENTS Glaciers might be more or less accessible, and weather 
MEASUREMENT conditions might be bad in altitude. Snow might also cover 
some of the reference points. 
Glaciers surface displacements can be monitored by different Aerial or satellite imagery may be used for such displacement 
ways: the traditional technique, still used today, consists into measurement. Their main advantage is their spatial coverage, 
placing reference points on the glacier surface, and potentially the whole glacier. Satellite radar interferometry 
measuring their position at different times of the year. Today, has been used for precise ice velocity measurement since 
with the use of differential GPS (D-GPS), one can achieve 1993 (Goldstein, 1993), and this technique is very adequate 
very precise measurement (a few centimetres error), yet for measuring small displacements (up to a few tens of cm), 
limited to a few points in the accessible part of the glaciers. on cloud covered areas. Therefore, this method has proved to 
be adequate to follow glaciers displacements over a few days. 
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