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Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at tidewater glaciers, with submarine melting proposed as a potential trigger of increased glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5 m d−1 near the glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3 m d−1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at tidewater glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.

Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at tidewater glaciers, with submarine melting proposed as a potential trigger of increased glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5m d-1 near the glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3m d-1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at tidewater glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords. Publisher PDF

International audience; – Les satellites radars altimètres permettent de quantifier la fonte de la glace terrestre, ainsi que son impact sur l'´ evolution du niveau des océans. L'objectif du traitement Swath développé pour les données interférométriques du satellite CryoSat-2, est d'augmenter la densité des mesures altimétriques, sans en augmenter le bruit. La selection des données non bruitées est basée ici uniquement sur la qualité de la phase mesurée, en faisant l'hypothèse que la phase est affine par morceaux. Cet algorithme permet ainsi d'améliorer la précision des MNE et des taux de changement d'´ elévation estimésestimés`estimésà partir des données d'´ elévation. Abstract – The radar altimeter satellites enable to quantify the melt of the Earth's land ice, and its impact on the evolution on the sea level rise. The goal of the Swath processing developed for the SARIn data of the CryoSat-2 satellite is to increase the density of the altimetric measurement without adding noise to the final products. The selection of the unnoisy data is made on the phase quality alone, making the hypothesis that the phase is a piecewise slope function. This algorithm increases the accuracy of the DEM and the rate of elevation change maps computed from elevation data.

– Les satellites radars altimètres permettent de quantifier la fonte de la glace terrestre, ainsi que son impact sur l'´ evolution du niveau des océans. L'objectif du traitement Swath développé pour les données interférométriques du satellite CryoSat-2, est d'augmenter la densité des mesures altimétriques, sans en augmenter le bruit. La selection des données non bruitées est basée ici uniquement sur la qualité de la phase mesurée, en faisant l'hypothèse que la phase est affine par morceaux. Cet algorithme permet ainsi d'améliorer la précision des MNE et des taux de changement d'´ elévation estimésestimés`estimésà partir des données d'´ elévation. Abstract – The radar altimeter satellites enable to quantify the melt of the Earth's land ice, and its impact on the evolution on the sea level rise. The goal of the Swath processing developed for the SARIn data of the CryoSat-2 satellite is to increase the density of the altimetric measurement without adding noise to the final products. The selection of the unnoisy data is made on the phase quality alone, making the hypothesis that the phase is a piecewise slope function. This algorithm increases the accuracy of the DEM and the rate of elevation change maps computed from elevation data.

Changes to the grounding line, where grounded ice starts to float, can be used as a remotely-sensed measure of ice-sheet susceptibility to ocean-forced dynamic thinning. Constraining this susceptibility is vital for predicting Antarctica's contribution to rising sea levels. We use Landsat imagery to monitor grounding line movement over four decades along the Bellingshausen margin of West Antarctica, an area little monitored despite potential for future ice losses. We show that ~65% of the grounding line retreated from 1990-2015, with pervasive and accelerating retreat in regions of fast ice flow and/or thinning ice shelves. Venable Ice Shelf confounds expectations in that despite extensive thinning, its grounding line has undergone negligible retreat. We present evidence that the ice shelf is currently pinned to a sub-ice topographic high which, if breached, could facilitate ice retreat into a significant inland basin, analogous to nearby Pine Island Glacier.

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International audience; MONITORING A GLACIER IN SOUTHEASTERN ICELAND WITH THE PORTABLE TERRESTRIAL RADAR INTERFEROMETER

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International audience; We use satellite observations to document rapid acceleration and ice loss from a formerly slow-flowing, marine-based sector of Austfonna, the largest ice cap in the Eurasian Arctic. During the past two decades, the sector ice discharge has increased 45-fold, the velocity regime has switched from predominantly slow (~ 101 m/yr) to fast (~ 103 m/yr) flow, and rates of ice thinning have exceeded 25 m/yr. At the time of widespread dynamic activation, parts of the terminus may have been near floatation. Subsequently, the imbalance has propagated 50 km inland to within 8 km of the ice cap summit. Our observations demonstrate the ability of slow-flowing ice to mobilize and quickly transmit the dynamic imbalance inland; a process that we show has initiated rapid ice loss to the ocean and redistribution of ice mass to locations more susceptible to melt, yet which remains poorly understood.

International audience; Himalayan glaciers are under pressure due to climate change but spatial and temporal characteristics of glaciers change are not very well constrained. The fate of Himalayan glaciers is particularly important for local populations and for understanding the various patterns of climate change in the region. Thus it is important to quantify their evolution over the last decades to be able to understand future dynamic. Recent studies focus only on restricted areas, over a short time­scale whereas the diversity of the himalayan glaciers requires to work on a global scale and a time scale that is larger than the climatic variability. Glaciers' velocity is an important variable to characterise glaciers' evolution and dynamics. The Landsat archive with its global coverage and 40 years of temporal coverage is a major EO dataset for improving the spatial and temporal resolution of Himalayan glaciers' change. Here we present the premice of a fully automated processing chain used to derive glacier velocity for the entire himalayan range for the period 1972-2013.

International audience; Here we present the first results of quality assessment of height retrieval by CryoSat­2 over the snow and ice covered Karakoram region. We simulate the successive areas tracked by CryoSat in SARIN mode, compare them to glacier regions and estimate the region of interest covered by CS2.

International audience; Climate warming over the 20th century has caused drastic changes in mountain glaciers globally, and of the Himalayan glaciers in particular. The stakes are high; mountain glaciers are the largest contributor to the increase in the mass of the world's oceans, and the Himalayas play a key role in the hydrology of the region, impacting on the economy, food safety and flood risk to a large population. Partial monitoring of the Himalayan glaciers has revealed a mixed picture; while many of the Himalayan glaciers are retreating, in some cases locally stable or advancing glaciers in this region have also been observed. Recent controversies around the future of the Himalayan glaciers, fuelled by projections reproduced in the 2007 Intergovernmental Panel on Climate Change report, have highlighted our limited knowledge of the evolution of Himalayan glaciers, and our limited understanding of the relationship between climate change and Himalayan glaciers' change. In its interferometric mode, CryoSat-2 is designed to enable the retrieval of elevation over steep sloping terrain. If successful over mountain glaciers, height retrieval by CryoSat-2 could provide an invaluable datasets for the assessment of ice mass balance of the Earth's mountain glaciers. Here we present the first results of quality assessment of height retrieval by CryoSat-2 over the snow and ice covered Himalaya.

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International audience

We use the Small BAseline Subset (SBAS) InSAR algorithm to obtain radar line-of-sight deformation velocities for two adjacent SAR swaths and invert the data for the 2-D velocity field in vertical and ground range direction. The analysis reveals areas of rapid deformation caused by mining and agricultural activities in the Crescent Valley, Nevada, USA. The LOS displacements of up to 25 centimeters during the 1992–2002 period are caused by vertical and horizontal deformation. About 8 mm/yr horizontal velocity is detected 10 km from the BARGEN GPS site LEWI suggesting that the GPS station may be moving in response to the water pumping. In the Basin and Range anthropogenic ground deformation can extend several tens of kilometers from the basins into the bedrock of the Ranges.