Monitoring Alpine Glacier activity by a combined use of TerraSAR-X images and continuous GPS measurements - the Argentière glacier experiment

Abstract

The monitoring of Alpine glacier activity is one of the applications which require the combined use of ground measurements and SAR data, and should become feasible thanks to the TerraSAR-X mission characteristics. The high resolution images and the relatively short repeat cycle will allow new investigations over moving glacier surface made of ice, firm, snow and rocks. Surface motion analysis will benefit from either the higher resolution or the dual polarization for feature tracking approaches and from the increased interferometric potential to obtain displacement fields by differential SAR Interferometry (D-InSAR). However, several difficulties have to be solved in order to obtain reliable displacement measurements over the fast moving Alpine glaciers. The three main limitations which affect the D-InSAR approach are the coherence preservation, the atmospheric artifacts and the unknown phase unwrapping offsets when the moving surface cannot be connected to a non-moving area. In order to investigate these issues on Alpine glaciers, series of TerraSAR-X images are expected to be acquired over the Chamonix Mont-Blanc test-site which includes well-known glaciers such as the Mer-de-Glace glacier (the second European largest glacier complex) and the Argentière glacier which has been monitored and instrumented for several decades by different scientific teams. Moreover, a corner reflector (CR) provided by the DLR and a continuous GPS recording station have been fixed on the ice on the upper part of the glacier during an E-SAR campaign in February 2007. Two other non-moving continuous GPS stations have been installed, one near the glacier at 2700 meter height and one down in the Chamonix valley. Despite the difficulties to maintain this equipment on the moving and changing glacier surface, it should allow us to perform several experiment based on the detection of the CR with a high accuracy in the TerraSAR-X images and the knowledge of its position by the GPS data. The CR displacement will be used either as ground truth for performance assessment or as complementary data for solving D-InSAR phase unwrapping ambiguity. The 3 continuous GPS stations will be used to study the electromagnetic path delay variations and to correct the atmospheric perturbations in the SAR based glacier motion measurements. This paper will present the experiment and the first result analysis from the data acquired during winter 2007/2008.