Bauer-Gottwein, Peter

Ingeman-Nielsen, Thomas

Paamand, Eskild

Tomaskovicova, Sonia

The sedimentary settings of West Greenlandic towns with their fine-grained, often ice-rich marine deposits are of great concern in building and construction projects in Greenland, as they lose volume, strength and bearingcapacity upon thaw. Since extensive permafrost thawing over large areas of inhabited Greenlandic coast has been predicted as a result of climate change, it is of great both technical and economical interest to assess the extentand thermal properties of such formations. Availability of methods able to determine the thermal parameters of permafrost and forecast its reaction to climate evolution is therefore crucial for sustainable infrastructure planningand development in the Arctic.We are developing a model of heat transport for permafrost able to assess the thermal properties of the ground based on calibration by surface geoelectrical measurements and ground surface temperature measurements. The advantages of modeling approach and use of exclusively surface measurements (in comparison with direct measurements on core samples) are smaller environmental impact, cheaper logistics, assessment of permafrost conditions over larger areas and possibility of forecasting of the fate of permafrost by application of climate forcing.In our approach, the heat model simulates temperature distribution in the ground based on ground surface temperature, specified proportions of the ground constituents and their estimated thermal parameters. The calculatedtemperatures in the specified model layers are governing the phase distribution between unfrozen water and ice. The changing proportion of unfrozen water content as function of temperature is the main parameter drivingthe evolution of electrical properties of the ground. We use a forward modeling scheme to calculate the apparent resistivity distribution of such a ground as if collected from a surface geoelectrical array. The calculated resistivityprofile is compared to actual field measurements and a difference between the synthetic and the measured apparent resistivities is minimized in a least-squares inversion procedure by adjusting the thermal parameters of the heatmodel. A site-specific calibration is required since the relation between unfrozen water content and temperature is strongly dependent on the grain size of the soil.We present details of an automated permanent field measurement setup that has been established to collect the calibration data in Ilulissat, West Greenland. Considering the station location in high latitude environment, this setup is unique of its kind since the installation of automated geophysical stations in the Arctic conditions is a challenging task. The main issues are related to availability of adapted equipment, high demand on robustness of the equipment and method due to the harsh environment, remoteness of the field sites and related powering issues of such systems.By showing the results from the new-established geoelectrical station over the freezing period in autumn 2012, we prove the 2D time lapse resistivity tomography to be an effective method for permafrost monitoring in high latitudes. We demonstrate the effectivity of time lapse geoelectrical signal for petrophysical relationship calibration, which is enhanced comparing to sparse measurements

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Coupled thermo-geophysical inversion for high-latitude permafrost monitoringassessment of the method and practical considerationsTomaskovicova, Sonia; Paamand, Eskild ; Ingeman-Nielsen, Thomas; Bauer-Gottwein, PeterPublished in:Geophysical Research AbstractsPublication date:2013Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Tomaskovicova, S., Paamand, E., Ingeman-Nielsen, T., & Bauer-Gottwein, P. (2013). Coupled thermo-geophysical inversion for high-latitude permafrost monitoring: assessment of the method and practicalconsiderations. Geophysical Research Abstracts, 15, [EGU2013-764].Geophysical Research AbstractsVol. 15, EGU2013-764, 2013EGU General Assembly 2013© Author(s) 2012. CC Attribution 3.0 License.Coupled thermo-geophysical inversion for high-latitude permafrostmonitoring – assessment of the method and practical considerationsSonia Tomaskovicova (1), Eskild Paamand (2), Thomas Ingeman-Nielsen (1), and Peter Bauer-Gottwein (2)(1) Technical University of Denmark, The Arctic Technology Centre, Department of Civil Engineering, Kgs. Lyngby,Denmark (soto@byg.dtu.dk), (2) Technical University of Denmark, Department of Environmental Engineering, Kgs. Lyngby,DenmarkThe sedimentary settings of West Greenlandic towns with their fine-grained, often ice-rich marine deposits areof great concern in building and construction projects in Greenland, as they lose volume, strength and bearingcapacity upon thaw. Since extensive permafrost thawing over large areas of inhabited Greenlandic coast has beenpredicted as a result of climate change, it is of great both technical and economical interest to assess the extentand thermal properties of such formations. Availability of methods able to determine the thermal parameters ofpermafrost and forecast its reaction to climate evolution is therefore crucial for sustainable infrastructure planningand development in the Arctic.We are developing a model of heat transport for permafrost able to assess the thermal properties of theground based on calibration by surface geoelectrical measurements and ground surface temperature measure-ments. The advantages of modeling approach and use of exclusively surface measurements (in comparisonwith direct measurements on core samples) are smaller environmental impact, cheaper logistics, assessment ofpermafrost conditions over larger areas and possibility of forecasting of the fate of permafrost by application ofclimate forcing.In our approach, the heat model simulates temperature distribution in the ground based on ground surfacetemperature, specified proportions of the ground constituents and their estimated thermal parameters. The calcu-lated temperatures in the specified model layers are governing the phase distribution between unfrozen water andice. The changing proportion of unfrozen water content as function of temperature is the main parameter drivingthe evolution of electrical properties of the ground. We use a forward modeling scheme to calculate the apparentresistivity distribution of such a ground as if collected from a surface geoelectrical array. The calculated resistivityprofile is compared to actual field measurements and a difference between the synthetic and the measured apparentresistivities is minimized in a least-squares inversion procedure by adjusting the thermal parameters of the heatmodel. A site-specific calibration is required since the relation between unfrozen water content and temperature isstrongly dependent on the grain size of the soil.We present details of an automated permanent field measurement setup that has been established to collectthe calibration data in Ilulissat, West Greenland. Considering the station location in high latitude environment,this setup is unique of its kind since the installation of automated geophysical stations in the Arctic conditions is achallenging task. The main issues are related to availability of adapted equipment, high demand on robustness ofthe equipment and method due to the harsh environment, remoteness of the field sites and related powering issuesof such systems.By showing the results from the new-established geoelectrical station over the freezing period in autumn2012, we prove the 2D time lapse resistivity tomography to be an effective method for permafrost monitoringin high latitudes. We demonstrate the effectivity of time lapse geoelectrical signal for petrophysical relationshipcalibration, which is enhanced comparing to sparse measurements.

Coupled thermo-geophysical inversion for high-latitude permafrost monitoring:assessment of the method and practical considerations

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Coupled thermo-geophysical inversion for high-latitude permafrost monitoring:assessment of the method and practical considerations

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