GPS and TerraSAR­X time series measure temperate glacier flow in the Mont Blanc massif (France): the Argentière glacier test site

International audienceWe present our study dealing with the surface velocity on the Argentiere glacier in the Mont Blanc massif, France obtains by SAR and GPS observations. We produce a surface velocity field using the offset power tracking technique on couples of descending and ascending TerraSAR-X acquisitions repeated at 11 days intervals. Moreover we dispose of four years of GPS data acquired continuously on the Argentière glacier. Our local permanent GPS network is composed of two stations on the glacier at altitudes of 2441 m and 2770 m, and two stations in static places, one in the valley of Chamonix at an altitude of 1121 m and the other on a rock outcrop near the glacier at the altitude of 2835 m. The measurements yield average displacement rates of about 13 cm/day for the upper glacier station (2770 m) and 17 cm/day for the lower site (2441 m). These in situ GPS results are used to strain image registration during SAR data processing and to make multi-dates and multi-spaces comparisons between profiles in the surface velocity field and GPS observation. The GPS analyse allow us to observe an annual variability of the displacement rates of up to 28 %, with fastest flow in late summer, while longitudinal profil of the surface velocity field allow us to observe a spatial variability of the displacement rates of up to 50%, with fastest flow at the top of the glacier. The continuous monitoring of the Argentière glacier flow over several annual cycles can now be used to determine the correlation with climatological parameters such as temperature and cumulated precipitations and to make models of displacement mechanisms occuring in temperate glaciers