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A comparison of seismic and radar methods to establish the thickness and density of glacier snow cover
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
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2013 (English)In: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 54, no 64, p. 73-82Article in journal (Refereed) Published
Abstract [en]

We show that geophysical methods offer an effective means of quantifying snow thickness and density. Opportunistic (efficient but non-optimized) seismic refraction and ground-penetrating radar (GPR) surveys were performed on Storglaciaren, Sweden, co-located with a snow pit that shows the snowpack to be 1.73 m thick, with density increasing from similar to 120 to similar to 500 kg m(-3) (with a +50 kg m(-3) anomaly between 0.73 and 0.83 m depth). Depths estimated for two detectable GPR reflectors, 0.76 +/- 0.02 and 1.71 +/- 0.03 m, correlate extremely well with ground-truth observations. Refraction seismic predicts an interface at 1.90 +/- 0.31 m depth, with a refraction velocity (3730 +/- 190 m s(-1)) indicative of underlying glacier ice. For density estimates, several standard velocity-density relationships are trialled. In the best case, GPR delivers an excellent density estimate for the upper snow layer (observed = 321 +/- 74 kg m(-3), estimated = 319 +/- 10 kg m(-3)) but overestimates the density of the lower layer by 20%. Refraction seismic delivers a bulk density of 404 +/- 22 kg m(-3) compared with a ground-truth average of 356 +/- 22 kg m(-3). We suggest that geophysical surveys are an effective complement to mass-balance measurements (particularly for controlling estimates of snow thickness between pits) but should always be validated against ground-truth observations.

Place, publisher, year, edition, pages
2013. Vol. 54, no 64, p. 73-82
National Category
Physical Geography Geosciences, Multidisciplinary
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-95097DOI: 10.3189/2013AoG64A044ISI: 000324720300010OAI: oai:DiVA.org:su-95097DiVA, id: diva2:658550
Note

AuthorCount:6;

Available from: 2013-10-22 Created: 2013-10-21 Last updated: 2018-04-17Bibliographically approved
In thesis
1. Studies in Glacier Mass Balance: Measurement and its errors
Open this publication in new window or tab >>Studies in Glacier Mass Balance: Measurement and its errors
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The study of the surface mass balance of valley glaciers has a long history but one that is dogged by uncertainty and errors, and uncertainty about those errors. These problems are acknowledged by the glaciological community and have been examined and formalised in several publications. The latest of these stems from a workshop organised by the World Glacier Monitoring Service, the results of which are presented in the first paper of this thesis. The paper examines two common methods and some of their associated errors, with the aim of unifying them and providing more robust data sets. New methodologies, such as ground penetrating radar (GPR), are used in the second paper herein to provide richer and alternative data sources for approaching measurement problems related to snow depth and, to some degree, snow density. The third paper is concerned with both technical survey issues and glaciological definitions when surveys of glacier surfaces are performed for use in mass balance calculation. Many of these issues are common to remote sensing methods and ground based surveys but the paper attempts to make this commonality more explicit. Whilst the first three papers concern themselves with the act of measurement and calculation the fourth paper considers errors brought about by logistical constraints restricting the timing of surveys. Such errors are technically avoidable to a large degree but inevitable in practice. In the case presented here the error is one of unobserved accumulation, falling late in the season, after the last survey. By modelling expected ablation from minimal data, such as temperature, and comparing this with measured mass balance an estimate of unobserved accumulation is made.

Also contained in this work is an assessment of glacier front surveys, specifically those performed by the Tarfala Research Station. Such surveys are assumed to act as a monitor of glacier response to climate change and are assumed to be a large scale proxy of mass balance but the resolution of the response as well as the resolution of survey methods indicates that the frequency of such surveys should be reduced and that remote sensing methods may be more effective.

Common to all glaciological field surveys is the relative sparsity of data rendering error analysis and many statistical methods ineffective but new technologies such as Lidar, Global Navigation Satellite System, GPR and remote sensing indicate a way forward and the potential for future work to deliver detailed and reliable data.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography, Stockholm University, 2018
Series
Dissertations from the Department of Physical Geography, ISSN 1653-7211 ; 72
Keyword
Glaciology, Mass Balance, Measurement Errors
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-155233 (URN)978-91-7797-205-1 (ISBN)978-91-7797-206-8 (ISBN)
Public defence
2018-06-11, Ahlmannsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
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Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2018-05-17 Created: 2018-04-16 Last updated: 2018-04-27Bibliographically approved

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