Showing papers by "Noel Gourmelen published in 2012"
TL;DR: In this article, the authors measured changes in the dynamics of the marine outlet glaciers of the Greenland and Antarctica ice sheets and their potential contributions to future sea level rise by collecting quantitative measurements within the dynamic environment.
Abstract: Recent melting in Greenland and Antarctica has led to concerns about the long-term stability of these ice sheets and their potential contributions to future sea level rise. Marine-terminating outlet glaciers play a key role in the dynamics of these ice sheets; recent mass losses are likely related to increased influx of warmer water to the base of outlet glaciers, as evidenced by the fact that changes in ocean currents, calving front retreats, glacial thinning, mass redistribution based on satellite gravity data, and accelerating coastal uplift are roughly concurrent [e.g., Holland et al., 2008; Wouters et al., 2008; Jiang et al., 2010; Straneo et al., 2012; Bevis et al., 2012]. However, collecting quantitative measurements within the dynamic environment of marine outlet glaciers is challenging. Oceanographic measurements are limited in iceberg-laden fjords. Measuring ice flow speeds near the calving front is similarly challenging; satellite methods lack temporal resolution (satellite revisit times are several days or longer), while GPS gives limited spatial resolution, a problem for assessing changes near the highly variable calving front.
20 citations
TL;DR: In this article, a method to determine two-dimensional ice-shelf flow vectors independently of model predictions of tide and atmospheric pressure, by stacking conventional and multiple aperture InSAR (MAI) observations of the Dotson Ice Shelf, was described.
Abstract: Interferometric synthetic aperture radar (InSAR) observations of ice-shelf flow contain ocean-tide and atmospheric-pressure signals. A model-based correction can be applied, but this method is limited by its dependency upon model accuracy, which in remote regions can be uncertain. Here we describe a method to determine two-dimensional ice-shelf flow vectors independently of model predictions of tide and atmospheric pressure, by stacking conventional and multiple aperture InSAR (MAI) observations of the Dotson Ice Shelf, West Antarctica. In this way we synthesize a longer observation period, which enhances long-period (flow) displacement signals, relative to rapidly varying (tide and atmospheric pressure) signals and noise.We estimate the error associated with each component of the velocity field to be ~22ma -1, which could be further reduced if more images were available to stack. With the upcoming launch of several satellite missions, offering the prospect of regular short-repeat SAR acquisitions, this study demonstrates that stacking can improve estimates of ice-shelf flow velocity.
20 citations
13 Nov 2012
TL;DR: In this article, the authors presented the first results of quality assessment of height retrieval by CryoSat-2 over the snow and ice covered Himalaya, which could provide an invaluable datasets for the assessment of ice mass balance of the Earth's mountain glaciers.
Abstract: 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.
18 citations
13 Nov 2012
TL;DR: In this paper, the first results of quality assessment of height retrieval by CryoSat-2 over the snow and ice covered Karakoram region were presented, where the successive areas tracked by the satellite in SARIN mode were compared to glacier regions and estimated the region of interest covered by CS2.
Abstract: 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.
15 citations
22 Jul 2012
TL;DR: This study uses the Gamma Portable Radar Interferometer (GPRI) to measure the velocity of Breidamerkurjokull, a marine-terminating outlet glacier on the southeastern coast of Iceland, and compares it to TerraSAR-X data taken shortly after, documenting significant temporal and spatial variability of ice velocity within 800 meters of the calving front.
Abstract: Terrestrial Radar Interferometry (TRI) has several advantages for measuring glacier velocity. These ground-based systems alleviate problems associated with the long revisit times of satellites, and provide higher spatial sampling compared to GPS-based approaches. TRI is the technique of choice for rapidly moving glaciers, especially their terminal zones, which tend to exhibit high spatial and temporal variability. In this study, we use the Gamma Portable Radar Interferometer (GPRI) to measure the velocity of Breidamerkurjokull, a marine-terminating outlet glacier on the southeastern coast of Iceland, and compare it to TerraSAR-X data taken shortly after. We document significant temporal and spatial variability of ice velocity within 800 meters of the calving front.
11 citations