QUATERNARY GEOLOGY
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IMERSUAQ |
A joint scientific project involving:
- IImersuaq - Climate and melting
- Airborne laser-altitude measurements
- Topografic and iceradar mapping
- Waterchemistry
- Ph.D. study
- People
Objects and methods:
- The project aims at a more precise estimate of the contribution from the icesheet to hydropower potentials, based on the largest basin in Western Greenland 'Tasersiaq', situated between the cities of Maniitsoq and Kangerlussuaq
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New methods applied:
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Detailed mapping of the icemargin using radar measurements from satellite.
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Airborne radio-echo soundings, precisely estimating the ice thickness and bedrock topography.
- Accurate determination of the aircraft's position by means of GPS and laser altimetry of the aircraft altitude above the ice.
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Detailed mapping of the icemargin using radar measurements from satellite.
- Furthermore, fully automatic climate stations on the surface provides in situ climate data for calculation of the snowmelt.
- The insight gained from combining the extensive data set with the broad range of expertise available within the project, is to be condensed into a strong scientific tool, which can be applied when the prospects for new hydropower plants in Greenland has to be assessed.
- It is costly to produce energy in Greenland, because it is rather isolated, and the population is very spread out
- Hydropower is already exploited in Nuuk and is by and large the only local source of energy in Greenland
- A greater utilization of the hydropower potential in Greenland would be a significant environmental gain, compared to the conventional diesel power plants
- he search for raw materials (such as oil, gold and diamonds) in and around Greenland in recent years, have made the establishment of energy-intensive industries more likely
- Establishing new hydropower plants calls for large investments, which requires assessments of the supply reliability; i.e. the availability of sufficient quantities of water at all times
- 20 years ago a number of investigations regarding the hydropower potential of Greenland, was carried out, these were limited by the available methods and knowledge
Imersuaq - Climate and melting - Field measurements 1999-2000 (ASIAQ & GEUS)
Setting up a climate station
Climate stations, as the one shown above, has been erected in 4 locations on the ice margin at Tasersiaq.
They are placed in a quadratic configuration because results from the initial phase have indicated a changes in climate- and melting conditions from north to south over the area. And we would like to estimate these changes more accurate.
In the field seasons of 1999 & 2000 a total of 10 ablation stakes has been drilled down in order to measure the melting in the area. In the same locations differential GPS-measurements have also been made along with collection of snow samples for chemical analysis. Furthermore a spectrometer was used to measure the reflection of the solar radiation (the albedo) over different snow and ice surfaces.
During the most recent visit (late August 2000), where stakes and climatestations were checked, data downloaded and instruments adjusted for the winter, it was found that the climate stations had been working as intended with the new mast concept (as seen in the picture above). At this time spectrometer measurements of the reflection was made again, close to the climate stations.
At the same time the run-off from the Tasersiaq basin in front of the ice is measured. This has been done for a number of years because of the great hydropower potential of the basin.
Furthermore Greenland Survey has carried out climatological measurements in the area over the past 25 years - a valuable dataset, which is an integrated part of the project, and the efforts to qualitatively, as well as quantitatively, describe the processes which are in play in this area, and their interactions.
These two series of measurements will naturally be continued and extended with additional stations and new equipment. In addition extensive analyses of the collected climatic and hydrological data will be made, among other things through studies of satellite images.
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FAirborne laser-altitude measurements - Late August 2000 (KMS)
The aircraft where the laser and the ice radar was mounted
The airborne laser measurements allow an ultra-precise determination of the elevation conditions on the Inland ice with a potential accuracy of 10-20 cm!
A laser altimeter gives a profile along the flight direction, with the altitude being measured 50 times each second, while the laser scanner gives a continuos transverse sweep. It was the first time the laser scanner was tested in Greenland, and it was successful: structures on the ice surface could be easily identified and good return signals were also seen over land.
Therefore laser scanning will be a suitable way of surveying the ice in Greenland.
The exact position and orientation of the aircraft is essential in order to be able to interpret data. Positioning, relative to 2 reference receivers in Kangerlussuaq, was done using two geodetic GPS receivers. Orientation, i.e. roll and pitch, was measured with two independent precision instruments (gyro/accelerometers) on board the aircraft.
The collected data has a number of applications:
- Composition of a general elevation map of the ice
- Comparison with elevations obtained from satellite based radar
- As a reference area for re-measurement to register elevation changes of the ice
Topographic and iceradar mapping - Late August 2000 (DCRS)
Map of the icesheet margin in the investigated area
- Flight tracks are shown in blue (bedrock echo detected) and red (no echo)
- Thin black lines are surface contours measured with ERS 1/2 interferometry (satellitebased radar)
- * The heavy black line indicates the ice margin
As a basis to determine a reasonable distance between the flight tracks we have carried out an analysis of an ice free area in front of the ice margin and of an ice covered area of the margin itself. Both analyses show characteristic wavelengths of the ground of 4-7 km. In order to be able to outline this largescale topography and at the same time cover the hydrological catchment area on the ice margin, a distance of 2,5 km between the flight tracks was chosen as a reasonable compromise between resolution and coverage.
Based on the pictures from the ERS 1/2 satellites' Synthetic Aperture Radar (SAR), a digital elevation model has been made, which is used to map the surface drainage pattern on the ice margin.
Furthermore the ice velocity on the margin has been determined from the SAR data, assuming that the ice is moving in the direction of maximum surface slope.
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Water chemistry - June-August 2000 (Geological Inst., Uni. of Aarhus)
IThe ice front
- The locality for meltwater studies is seen by the glacier margin in the center of the picture
- The section of the glacier margin shown is about 2.5 km wide
Altogether 10 snow samples were collected in connection with a visit of the climate stations in the beginning of June. The samples were collected close to the glacier front and 2 kilometers above the front, near the central axis of the glacier.
In the investigated area, generally less than 60 centimeters of snow was observed.
During the middle of summer a camp was established just below the ice front, in preparation for the collection of watersamples. These watersamples were collected in a meltwater stream which clearly had an origin below the ice, since the water had a significant content of sediments and came out under the glacierfront. At the same time, water level, conductivity and water temperature were measured every 10 minutes over a period of 12 days.
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Ph.D. study (1999-2002)
Working title: Estimation of ice sheet ablation from remote sensing analysis and energy balance modelling.
Distributed energy-balance modelling showing:
- Ice sheet ablation
- bservation transects in blue
- Two possible basin delineations
The Ph.D. project is part of the IMERSUAQ project to determine the Inland Ice meltwater contribution to the Tasersiaq basin in West Greenland, funded by the Danish Natural Science Research Council. The goal of the Ph.D. project is to relate energy balance modelling, field observations and remotely sensed data for the dual purpose of mass balance modelling in the context of climate change and run-off estimation for hydro-power feasibility studies.
An ambitious field programme involving several institutions will provide the necessary data, including a detailed digital elevation model (DEM) and surface velocity field acquired from airborne laser altimetry and spaceborne InSAR, a series of ice sheet mass balance and climatological measurements from automatic weather stations and field work, an investigation of meltwater chemistry to determine origin, melt event timing and conduit structure and finally a continous record of basin water discharge. Albedo distribution is to be retrieved from NOAA-AVHRR (temporal) and Landsat 7 ETM+/Terra ASTER (spatial). Additional information about melt extent is attainable from passive microwave sensing and analysis of the extensive amount of SAR data collected could provide new applications to mass balance modelling, such as penetration characteristics, surface properties and velocity field calculations.
The climate data and the DEM are to be utilised in a distributed energy balance model to determine the ablation rate of the ice sheet in that particular region. The idea is to integrate the ablation information with the hydrological measurements, the meltwater chemistry investigations and the surface velocity field to obtain an overview of the processes governing the mass balance of the Greenland Ice Sheet and to assess the feasibility of determining ice sheet mass balance solely by remote sensing methods. The accomplishment of this goal would lend confidence to the reliability of investigations on the influence of climate change on the great ice sheets, which in turn governs sea level changes, and would shed light on the direction of the observed holocene climate variability. Simultaneously, it is the ambition to ease the estimation of the meltwater contribution from the Greenland Ice Sheet to hydrological basins under investigation for hydro-power potential. The desired outcome is a sort of white book which would be useful for the Greenland authorities, represented by the Greenland Survey (ASIAQ).
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People:
Greenland Survey (ASIAQ)
Maria Plougmann Hag
Asiaq
Postbox 1003
3900 Nuuk
Greenland
Jørgen Bille Hansen
Asiaq
Postbox 1003
3900 Nuuk
Greenland
Håkon Gjessing Karlsen
Asiaq
Postbox 1003
3900 Nuuk
Greenland
Danish Center for Remote Sensing (DCRS)
Niels Reeh , Associate Research Professor
Electromagnetic Systems
Technical University of Denmark
Ørsteds Plads, Building 348
DK-2800 Lyngby
Johan Jacob Mohr , Associate Professor
lectromagnetic Systems
Technical University of Denmark
Ørsteds Plads, Building 348
DK-2800 Lyngby
Geological Survey of Denmark and Greenland (GEUS)
Andreas Peter Ahlstrøm , Ph.D. Student
GEUS
Øster Voldgade 10
DK-1350 København
Carl Egede Bøggild , Research Scientist
GEUS
Øster Voldgade 10
DK-1350 København
Ole Brundthagen Olesen , Senior Consultant
GEUS
Øster Voldgade 10
DK-1350 København
Danish National Survey and Cadastre (KMS)
Rene Forsberg , State Geodesist
Danish National Survey and Cadastre
Rentemestervej 8
DK-2400 København NV
Kristian Keller , Student
Danish National Survey and Cadastre
Rentemestervej 8
DK-2400 København NV
Geological Institute, University of Aarhus
Niels Tvis Knudsen , Associate Professor
Geological Institute
University of Aarhus
Ny Munkegade, Building 520
DK-8000 Aarhus C
