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 to sea level rise. Publicly available DEMs derived from submeter 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 programme acquiring Pléiades stereo pairs for 140 sites from Earth's glacierized areas. The PGO product consists of DEMs at 2 m and 20 m ground sampling distance together with 0.5 m (panchromatic) and 2 m (multispectral) ortho-images. The DEMs are freely available to all registered users whereas ortho-images are available after signing a licence. PGO commenced in July 2016 in the North Hemisphere and February 2017 in the South Hemisphere. Each site is revisited every five 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 m a^-1. PGO samples over 20,000 km² of glacierized terrain which represents about 3 % of the Earth's glaciers area. This small sample, however, provides a first order estimate of the global glacier mass change and its decadal evolution. [ABSTRACT FROM AUTHOR]