The Pléiades Glacier Observatory: High-resolution digital elevation models and ortho-imagery to monitor glacier change

Spaceborne digital elevation models (DEMs) of glaciers are essential to describe their health and their contribution to river runoff and sea level rise. Publicly available DEMs derived from sub-meter satellite stereo imagery were, up to now, mainly available in the polar regions and High Mountain Asia. Here, we present the Pléiades Glacier Observatory (PGO), a scientific program acquiring Pléiades 0.7 m satellite stereo pairs for 140 sites from Earth's glacierized areas. The PGO product consists of freely available DEMs at 2 and 20 m ground sampling distance together with 0.5 m (panchromatic) and 2 m (multispectral) ortho-images. PGO stereo acquisitions began in July 2016 in the Northern Hemisphere and February 2017 in the Southern Hemisphere. Each site is revisited every 5 years (cloud permitting), close to the end of the melt season, to measure glacier elevation change with an average uncertainty of 0.49 m (95 % confidence level, for a glacierized area of 1 km2), i.e., 0.1 myr-1. PGO samples over 20 000 km2 of glacierized terrain, which represents about 3 % of the Earth's glacier area. This small sample, however, provides a first-order estimate (within 0.07 mw.e.yr-1) of the global glacier mass change and its decadal evolution.