Glacier topography and elevation changes derived from Pleiades sub-meter stereo images

In response to climate change, most glaciers are losing mass and hence contribute to sea-level rise. Repeated and accurate mapping of their surface topography is required to estimate their mass balance and to extrapolate/calibrate sparse field glaciological measurements. In this study we evaluate the potential of sub-meter stereo imagery from the recently launched Pleiades satellites to derive digital elevation models (DEMs) of glaciers and their elevation changes. Our five evaluation sites, where nearly simultaneous field measurements were collected, are located in Iceland, the European Alps, the central Andes, Nepal and Antarctica. For Iceland, the Pleiades DEM is also compared to a lidar DEM. The vertical biases of the Pleiades DEMs are less than 1m if ground control points (GCPs) are used, but reach up to 7m without GCPs. Even without GCPs, vertical biases can be reduced to a few decimetres by horizontal and vertical co-registration of the DEMs to reference altimetric data on ice-free terrain. Around these biases, the vertical precision of the Pleiades DEMs is +/- 1m and even +/- 0.5m on the flat glacier tongues (1 sigma confidence level). Similar precision levels are obtained in the accumulation areas of glaciers and in Antarctica. We also demonstrate the high potential of Pleiades DEMs for measuring seasonal, annual and multi-annual elevation changes with an accuracy of 1m or better if cloud-free images are available. The negative region-wide mass balances of glaciers in the Mont-Blanc area (-1.04 +/- 0.23 ma(-1) water equivalent, w.e.) are revealed by differencing Satellite pour l'Observation de la Terre 5 (SPOT 5) and Pleiades DEMs acquired in August 2003 and 2012, confirming the accelerated glacial wastage in the European Alps.