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  • 1
    Online Resource
    Online Resource
    BMBF F & E Verbundvorhaben "Tibet und Zentralasien: Monsun-Dynamik und Geoökosysteme" - Verbundvorhaben "Variabilität und Trends der Wasserhaushaltskomponenten in Benchmark-Einzugsgebieten des Tibet-Plateaus (WET)" : Abschlussbericht : Teilprojekt 4: hydrologische Fernerkundung : Projektlaufzeit: Originalantrag: 01.05.2011-30.04.2014, Aufstockungsantrag: 01.05.2014-31.12.2014 = [Tibet and Central Asia: monsoon dynamics and geoecosystems, joint project "variability and trends of water balance components in benchmark-catchments of the Tibetan plateau (WET), final report, subproject 4: hydrological remote sensing] (2015)
    Tübingen : Lehrstuhl Geoinformatik, Geographisches Institut, Universität Tübingen
    Details Availability
    Keywords: Forschungsbericht ; Monsun
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (18 Seiten, 2,27 MB) , Illustrationen, Diagramme
    URL: https://edocs.tib.eu/files/e01fb16/85947934X.pdf
    URL: https://doi.org/10.2314/GBV:85947934X
    DOI: 10.2314/GBV:85947934X
    Language: German
    Note: Förderkennzeichen BMBF 03G0804D. - Verbund-Nummer 01091668 , [Paralleltitel dem englischen Berichtsblatt des Prints entnommen]
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  • 2
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    Elastic deformation plays a non-negligible role in Greenland’s outlet glacier flow (2021)
    Christmann, Julia ; Helm, Veit ; Khan, Shfaqat Abbas ; [et al.]
    Nature Publishing Group UK
    Details
    Publication Date: 2023-11-13
    Description: Future projections of global mean sea level change are uncertain, partly because of our limited understanding of the dynamics of Greenland’s outlet glaciers. Here we study Nioghalvfjerdsbræ, an outlet glacier of the Northeast Greenland Ice Stream that holds 1.1 m sea-level equivalent of ice. We use GPS observations and numerical modelling to investigate the role of tides as well as the elastic contribution to glacier flow. We find that ocean tides alter the basal lubrication of the glacier up to 10 km inland of the grounding line, and that their influence is best described by a viscoelastic rather than a viscous model. Further inland, sliding is the dominant mechanism of fast glacier motion, and the ice flow induces persistent elastic strain. We conclude that elastic deformation plays a role in glacier flow, particularly in areas of steep topographic changes and fast ice velocities.
    Description: Ice flow dynamics in Greenland’s outlet glaciers are influenced by elastic deformation, both in the area of tidal influence up to 14 km inland from the grounding line and further upstream, suggest analyses of GPS observations and numerical simulations.
    Description: Bundesministerium für Bildung und Forschung (Federal Ministry of Education and Research) https://doi.org/10.13039/501100002347
    Description: European Union’s Horizon 2020 Research and Innovation Programme
    Description: https://doi.org/10.1594/PANGAEA.928940
    Description: https://nsidc.org/data/IDBMG4
    Description: https://gitlab.awi.de/jchristm/viscoelastic-79ng-greenland
    Description: https://doi.org/10.5281/zenodo.5507115
    Description: https://doi.org/10.5281/zenodo.5506953
    Keywords: ddc:551.31 ; Climate change ; Cryospheric science ; Hydrology
    Language: English
    Type: doc-type:article
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  • 3
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    Surface energy and mass balance at Purogangri ice cap, central Tibetan Plateau, 2001–2011 (2015)
    Cambridge University Press
    Details
    Publication Date: 2015-12-21
    Print ISSN: 0022-1430
    Electronic ISSN: 1727-5652
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of The International Glaciological Society (IGS).
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  • 4
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    Recent slowdown and thinning of debris-covered glaciers in south-eastern Tibet (2017)
    Elsevier
    In:  EPIC3Earth and Planetary Science Letters, Elsevier, 464, pp. 95-102
    Details
    Publication Date: 2017-04-18
    Description: Recent large-scale remote sensing studies have shown that glacier mass loss in south-eastern Tibet, specifically in the eastern Nyainqêntanglha Range exceeds the average in High Asia. However, detailed studies at individual glaciers are scarce and the drivers behind the observed changes are poorly constrained to date. Employing feature tracking techniques on TerraSAR-X data for the periods 2008/2009, 2012/2013 and 2013/2014 we found measurable surface velocities through to the glacier terminus positions of five debris-covered glacier tongues. This is contrary to debris-covered glaciers in other parts of High Asia, where stagnant glacier tongues are common. Our feature tracking results for the 2013/2014 period suggest an average deceleration of 51% when compared with published Landsat velocities for the period 1999/2003. Further, we estimated surface elevation changes for the five glaciers from recently released one arc second resolution elevation data obtained during the Shuttle Radar Topography Mission in 2000 and an interferometrical derived TanDEM-X elevation model for the year 2014. With an average rate of −0.83 ± 0.57 m a^-1 we confirm strong surface lowering in the region, despite the widely discussed insulation effect of debris cover. Beside the influence of thermokarst processes and delayed response times of debris-covered glaciers, we highlight that abundant monsoonal summer rainfall might contribute significantly to the pronounced negative mass balances in the study region.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Detecting high spatial variability of ice-shelf basal mass balance (2018)
    In:  EPIC3EGU General Assembly, Vienna, 2018-04-08-2018-04-13
    Details
    Publication Date: 2019-08-21
    Description: Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e. the difference between refreezing and melting. Here, we present an improved technique – based on satellite observations – to capture the small-scale variability in the BMB of ice shelves. We use mass conservation in a Lagrangian framework based on high-resolution surface velocities, atmospheric-model surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which preserves abrupt changes inflow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. After testing our technique on the Roi Baudouin Ice Shelf, East Antarctica, we test our methodology on other ice shelves, with different flow regimes. Whereas the detected large-scale pattern in the BMB is very similar to previous and coarser studies, we are nevertheless able detect small-scale features in the BMB with unprecedented detail (10 m gridding). Examples include elevated melting at an ice-shelf channel’s flank and surface lowering of an elliptical surface depression. Although the absolute, satellite-based BMB values remain uncertain, we have high confidence in the spatial variability on sub-kilometre scales. This work highlights expected challenges for a full coupling between ice and ocean models.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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  • 6
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    Fully Automated Detection of Supraglacial Lake Area for Northeast Greenland Using Sentinel-2 Time-Series (2021)
    In:  EPIC3Remote Sensing, 13, pp. 205
    Details
    Publication Date: 2021-02-01
    Description: The usability of multispectral satellite data for detecting and monitoring supraglacial meltwater ponds has been demonstrated for western Greenland. For a multitemporal analysis of large regions or entire Greenland, largely automated processing routines are required. Here, we present a sequence of algorithms that allow for an automated Sentinel-2 data search, download, processing, and generation of a consistent and dense melt pond area time-series based on open-source software. We test our approach for a ~82,000 km2 area at the 79°N Glacier (Nioghalvfjerdsbrae) in northeast Greenland, covering the years 2016, 2017, 2018 and 2019. Our lake detection is based on the ratio of the blue and red visible bands using a minimum threshold. To remove false classification caused by the similar spectra of shadow and water on ice, we implement a shadow model to mask out topographically induced artifacts. We identified 880 individual lakes, traceable over 479 time-steps throughout 2016-2019, with an average size of 64,212 m2. Of the four years, 2019 had the most extensive lake area coverage with a maximum of 333 km2 and a maximum individual lake size of 30 km2. With 1.5 days average observation interval, our time-series allows for a comparison with climate data of daily resolution, enabling a better understanding of short-term climate-glacier feedbacks.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    Evidence for a grounding line fan at the onset of a basal channel under the ice shelf of Support Force Glacier, Antarctica, revealed by reflection seismics (2021)
    In:  EPIC3The Cryosphere, 15(3), pp. 1517-1535, ISSN: 1994-0424
    Details
    Publication Date: 2021-04-19
    Description: Curvilinear channels on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the grounding line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–ocean evolution of the basal channels is required to understand the present behaviour and future dynamics of ice sheets and ice shelves. Here, we present focused active seismic and radar surveys of a basal channel, ∼950 m wide and ∼200 m high, and its upstream continuation beneath Support Force Glacier, which feeds into the Filchner Ice Shelf, West Antarctica. Immediately seaward from the grounding line, below the basal channel, the seismic profiles show an ∼6.75 km long, 3.2 km wide and 200 m thick sedimentary sequence with chaotic to weakly stratified reflections we interpret as a grounding line fan deposited by a subglacial drainage channel directly upstream of the basal channel. Further downstream the seabed has a different character; it consists of harder, stratified consolidated sediments, deposited under different glaciological circumstances, or possibly bedrock. In contrast to the standard perception of a rapid change in ice shelf thickness just downstream of the grounding line, we find a flat topography of the ice shelf base with an almost constant ice thickness gradient along-flow, indicating only little basal melting, but an initial widening of the basal channel, which we ascribe to melting along its flanks. Our findings provide a detailed view of a more complex interaction between the ocean and subglacial hydrology to form basal channels in ice shelves.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Ice flow and the conditions of the ice-bed interface at the onset of the Northeast Greenland Ice Stream (2020)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2020 - Online Everywhere, Online, 2020-12-01-2020-12-17American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component contributing to the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The ice stream geometry and surface velocities in the onset region of the NEGIS are not yet sufficiently well reproduced by ice sheet models. We present an assessment of the basal conditions of the onset region in a systematic analysis of airborne ultra-wideband radar data. Our data yield a new detailed model of ice-thickness distribution and basal topography in the upstream part of the ice stream. We observe a change from a smooth to a rougher bed where the ice stream widens from 10 to 60 km, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. The observation of off-nadir reflections that are symmetrical to the bed reflection in the radargrams suggests that these structures are elongated subglacial landforms, which in turn indicate potential streamlining of the bed. Together with basal water routing pathways, our observations hint to two different zones in this part of the NEGIS: an accelerating and smooth upstream region, which is collecting water, with reduced basal traction, and in the further downstream part, where the ice stream is slowing down and is widening, with a distribution of basal water towards the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 9
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    3D-Structure ofNEGIS shearmarginsfromradarstratigraphy (2020)
    In:  EPIC3EGU General Assembly 2020 | Sharing Geoscience Online, 2020-05-04-2020-05-08
    Details
    Publication Date: 2020-05-11
    Description: The North East Greenland Ice Stream (NEGIS) is delineated by well-defined shear margins, which are evident in the gradient of surface velocity field as well as in the surface topography, where they form troughs up to ten meters deep. In the upper part of the ice stream the margins appear not to be linked to bedrock topography. To understand this efficient system of mass transport towards the ocean it is essential to investigate the nature of the shear margins, as here very localized deformation decouples the inner ice stream from the slower flowing surrounding ice sheet. This process is influenced by several factors and feedback mechanisms, including the crystal fabric orientation, strain heating and localization of meltwater. In summary, the shear margins are area-wise a small part of the ice stream itself, but the processes leading to the localization of deformation are of similar importance for ice discharge as the processes enabling fast flow of the main trunk over the bed. We present results from an airborne radar survey with the AWI Ultra-Wide Band Radar system, covering an area 150 km upstream and 100 km downstream of the deep drilling site on the ice stream (EGRIP). Over the survey area the ice stream accelerates from 12 m/a to 75 m/a. We focus on the signatures of the shear margins in the radar data. In the regions of localized shear, the internal reflections in the radargrams show disturbances in the form of steep undulations, or chevron folds, which are intensified with ongoing shear. As the ice stream has been covered with 36 flow-perpendicular radar sections we are able to show the evolution of these characteristic signatures over the survey area, and thus, as an analog, over time. 3D-representations of the folded stratigraphic layers reveal how new folds are formed when the ice stream widens and how older structures are preserved in the outer part of the main trunk, where they are no longer subject to shear. Furthermore, we link the change of the shape of the internal reflections in the shear zones to a strain rate field calculated from high resolution flow velocities derived by TerraSAR-X data.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 10
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    Seasonal Observations at 79°N Glacier (Greenland) From Remote Sensing and in situ Measurements (2020)
    In:  EPIC3Frontiers in Earth Science, 8, pp. 142
    Details
    Publication Date: 2020-06-17
    Description: This study investigates seasonal ice dynamics of Nioghalvfjerdsfjorden or 79°N Glacier, one of the major outlet glaciers of the North East Greenland Ice Stream. Based on remote sensing data and in-situ GPS measurements we show that surface melt water is quickly routed to the ice-bed interface with a direct response on ice velocities measured at the surface. From the temporally highly resolved GPS time series we found summer peak velocities of up to 22 faster than their winter baseline. These average out to 9 above winter velocities when relying on temporally lower resolved velocity estimates from TerraSAR-X intensity offset tracking. From our GPS time series we also found short term ice acceleration after the melt season. By utilizing optical satellite imagery and interferometrically derived digital elevation models we were able to link the post melt season speed-up to a rapid lake drainage event (〈24 h) with an estimated drainage volume of 28x10⁶ m³. We further highlight that GPS measurements are needed to resolve short term velocity fluctuations with low amplitudes, whereas remote sensing estimates are rather useful for the calculation of general trends in velocity behavior.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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