Measurement of Glacier Velocity Fields Using Very Precise Multitemporal Correlation on High Resolution Spot5 Images

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 SPOT5 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.