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Mass balances of the Glacier Blanc between 1952, 1981 and 2002 calculated from digital elevation models

Bilans de masse du Glacier Blanc entre 1952, 1981 et 2002 obtenus par modèles numériques de terrain

Abstract : Three Digital Elevation Models (DEM) of the Glacier Blanc have been calculated using photogrammetric restitutions of aerial photographs realised in 1952, 1981 and 2002 by IGN (the French administration for geography) and SINTEGRA (private company, Meylan, France). The aerial triangulation and the orientation of the stereographic images based on GPS control points lead to an absolute orientation whose residual standard deviation is between 0.25 to 1.25 m in planimetry and between 0.4 and 1.55 m in altitude (Lambert III, IGN69). Spot heights and 5 meter contour lines have been drawn (120 points/ha) which enables to build a Triangular Irregular Network (TIN) according to Delauney algorithm. This vector network has been linearly interpolated to obtain a DEM which is a raster grid of 10 meter spatial resolution. The subtraction of those DEM yields altitudinal variations on the surface of the glacier from which cumulative mass balance has been deduced. Results show a mass balance increasing of 2.1 m between 1952 and 1981 and decreasing of 10.8 m between 1981 and 2002. Results are compared with those of neighbour glaciers.