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Marti R.,Geographie de lEnvironnement GEODE | Marti R.,CNRS Center for the Study of the Biosphere from Space | Gascoin S.,CNRS Center for the Study of the Biosphere from Space | Houet T.,Geographie de lEnvironnement GEODE | And 2 more authors.
Revue Francaise de Photogrammetrie et de Teledetection | Year: 2014

Glaciers mass balances are recognized as good regional climate proxies. A glacier mass balance can be obtained by calculating the difference between two consecutive digital elevation models assuming a surface glacier density. Hence accurate and high resolution DEMs are particularly valuable data in glaciology. A Pléiades stereo pair was acquired over Ossoue Glacier (French Pyrenees) in September 2013. We generated a 2m horizontal resolution DEM with a 1m vertical resolution. Shortly after, a DGPS survey on Ossoue glacier and its periphery allowed us to estimate the Pléiades DEM vertical error of ±1,8m. We conclude that Pléiades stereoscopic images can be used for accurate mountain glaciers mass balances determination. Source

Szczypta C.,CNRS Center for the Study of the Biosphere from Space | Gascoin S.,CNRS Center for the Study of the Biosphere from Space | Houet T.,Geographie de lEnvironnement GEODE | Hagolle O.,CNRS Center for the Study of the Biosphere from Space | And 3 more authors.
Journal of Hydrology | Year: 2015

The seasonal snow in the Pyrenees Mountains is an essential source of runoff for hydropower production and crop irrigation in Spain and France. The Pyrenees are expected to undergo strong environmental perturbations over the 21st century because of climate change (rising temperatures) and the abandonment of agro-pastoral areas (reforestation). Both changes are happening at similar timescales and are expected to have an impact on snow cover. The effect of climate change on snow in the Pyrenees is well understood, but the effect of land cover changes is much less documented. Here, we analyze the response of snow cover to a combination of climate and land cover change scenarios in a small Pyrenean catchment (Bassiès, 14.5km2, elevation range 940-2651m a.s.l.) using a distributed snowpack evolution model. Climate scenarios were constructed from the output of regional climate model projections, whereas land cover scenarios were generated based on past observed changes and an inductive pattern-based model. The model was validated over a snow season using in situ snow depth measurements and high-resolution snow cover maps derived from SPOT (Satellite Pour l'Observation de la Terre - Earth Observation Satellite) satellite images. Model projections indicate that both climate and land cover changes reduce the mean snow depth. However, the impact on the snow cover duration is moderated in reforested areas by the shading effect of trees on the snow surface radiation balance. Most of the significant changes are expected to occur in the transition zone between 1500m a.s.l. and 2000m a.s.l. where (i) the projected increase in air temperatures decreases the snow fraction of the precipitation and (ii) the land cover changes are concentrated. However, the consequences on the runoff are limited because most of the meltwater originates from high-elevation areas of the catchment, which are less affected by climate change and reforestation. © 2014 Elsevier B.V. Source

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