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Multi-temporal, multi-sensor investigations of supra-glacial lakes on the Greenland Ice Sheet
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. (Glaciologi)
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. (Glaciologi)
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. (Glaciologi)
2011 (English)In: Proceedings of ESA Living Planet Symposium: 28 June - 2 July 2010, Bergen, Norway(DVD) / [ed] H. Lacoste-Francis, Noordwijk: ESA (European Space Agency) , 2011Conference paper, Published paper (Other academic)
Abstract [en]

The stability of the ice sheets is affected by the ongoing climate change through changes in the meltwater budget and effects on ice sheet dynamics. Surface lakes on the Greenland Ice Sheet have attracted much attention, but assessing their number and size as well as the variability over time of these parameters is not straight-forward. We present a satellite image-based survey of the total lake area and number of supra-glacial lakes in a specific region on the western margin of the Greenland Ice Sheet. Optical images from two different sensors (Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat) and images from three different synthetic aperture radar (SAR) satellites (Radarsat, ERS and Envisat) from 2001, 2006 and 2007, were used in order to manually digitize the extent of supra-glacial lakes. The image spatial resolution ranges from high (Radarsat, ERS and Landsat) to moderate (Envisat and MODIS) where high resolution corresponds to 6.25 to 25 m, and a moderate resolution corresponds to 50 to 250 m. SAR imagery was tested as a supplement to the more commonly used optical data to fill gaps in the time series caused by frequent cloud cover. In total 709 individual lakes were studied. High resolution images were shown to be preferable in the beginning of the melt season, due to the smaller size of the lakes. In the middle of the melt season the resolution was of limited importance. Our work suggests that the use of a combination of active radar and optical images enables successful lake monitoring with high temporal and spatial resolution in both cloudy and clear weather conditions.

Place, publisher, year, edition, pages
Noordwijk: ESA (European Space Agency) , 2011.
Keyword [en]
Greenland, Remote Sensing, SAR, supra-glacial lakes
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-74504ISBN: 978-92-9221-250-6 (print)OAI: oai:DiVA.org:su-74504DiVA: diva2:510104
Conference
ESA Living Planet Symposium: 28 June - 2 July 2010, Bergen, Norway
Available from: 2012-03-15 Created: 2012-03-15 Last updated: 2012-03-16Bibliographically approved
In thesis
1. Remote sensing of supra-glacial lakes on the west Greenland Ice Sheet
Open this publication in new window or tab >>Remote sensing of supra-glacial lakes on the west Greenland Ice Sheet
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Greenland Ice Sheet is the largest ice sheet in the northern hemisphere. Ongoing melting of the ice sheet, resulting in increased mass loss relative to the longer term trend, has raised concerns about the stability of the ice sheet. Melt water generated at the surface is temporarily stored in supra-glacial lakes on the ice sheet. Connections between melt water generation, storage and ice sheet dynamics highlight the importance of the surface hydrological system.

In this thesis different methods are used that improve our ability to observe the supra-glacial lake system on the west Greenland Ice Sheet. This region of the Greenland Ice Sheet has the most extensive supra-glacial hydrological system with a dense network of streams connecting lakes that can exceed several square kilometres in area. Synthetic Aperture Radar (SAR) and visible-near infrared (VNIR) images are used to explore the potential of different sensor systems for regular observations of the supra-glacial lakes. SAR imagery is found to be a useful complement to VNIR data. VNIR data from moderate resolution sensors are preferred as these provide high temporal resolution data, ameliorating problems with cloud cover.

The dynamic nature of the lakes makes automated classification difficult and manual mapping has been widely used. Here a new method is proposed that improves on existing methods by automating the identification and classification of lakes, and by introducing a flexible system that can capture the full range of lake forms. Applying our new method we are better able to analyse the evolution of lakes over a number of melt seasons. We find that lakes initiate after approximately 40 positive degree days. Most lakes exist for less than 20 days before draining, or later in the season, and less often, freezing over. Using the automated method developed in this thesis lakes have been mapped in imagery from 2001–2010 at approximately five day intervals.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology (INK), Stockholm University, 2012. 28 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 31
Keyword
Supra-glacial lakes, Greenland Ice Sheet, Ice melting, Remote sensing, SAR, MODIS, Time-series analysis
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-74509 (URN)978-91-7447-465-7 (ISBN)
Public defence
2012-04-20, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2012-03-29 Created: 2012-03-15 Last updated: 2013-04-02Bibliographically approved

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