Preprints
https://doi.org/10.5194/tc-2019-60
https://doi.org/10.5194/tc-2019-60

  16 May 2019

16 May 2019

Review status: this preprint has been withdrawn by the authors.

The response of supraglacial debris to elevated, high frequencyGPR: Volumetric scatter and interfacial dielectric contrastsinterpreted from field and experimental studies

Alexandra Giese1, Steven Arcone2, Robert Hawley1, Gabriel Lewis1, and Patrick Wagnon3 Alexandra Giese et al.
  • 1Department of Earth Sciences, Dartmouth College, Hanover, NH USA
  • 2Thayer School of Engineering, Dartmouth College, Hanover, NH USA
  • 3Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, F-38000 Grenoble, France

Abstract. The thickness of supraglacial debris affects the surface energy balance and retreat patterns of mountain glaciers. Therefore, knowing a debris layer’s thickness is crucial for understanding the magnitude and timeframe of glacier melt. Field- based ground-penetrating radar (GPR) has recently gained attention as a possible method for measuring debris thickness. Airborne assessments achieve extensive coverage and characterization, but the use of GPR for such platforms remains relatively unexplored. We investigated the performance of 960 MHz and 2.6 GHz GPR signals through dry laboratory rock debris, and of 960 MHz over ∼ 2 km of transects on the debris cover of Changri Nup Glacier, Nepal Himalaya. On the glacier, 960 MHz profiles were characterized by no clear reflection from the ice interface and volumetric backscatter from within ∼ 10–40 cm, a depth that corresponds to approximate ground-truth debris thicknesses on all transects. The laboratory results show that the lack of an ice-debris interface return in field data was likely caused by a weak dielectric contrast between solid ice and porous dry debris and that surface scatter is coherent but weak. This suggests that the debris-ice interface reflection was also likely coherent, supporting our conclusion of a weak dielectric contrast. The laboratory 2.6 GHz results show significant penetration for only smaller clast sizes up to 4 cm. We used a statistical approach to estimate ice depth from volumetric scatter, which gave reasonable agreement with ground-truth depth measurements. We conclude that a remote system operating near 1 GHz could successfully estimate dry debris cover thicknesses based on depth of volumetric backscatter.

This preprint has been withdrawn.

Alexandra Giese et al.

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Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Alexandra Giese et al.

Alexandra Giese et al.

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This preprint has been withdrawn.

Short summary
This manuscript defines a novel method of determining the depth of debris on a debris-covered glacier using 960 MHz Ground-Penetrating Radar, under circumstances which prevent the detection of a coherent reflection at the debris-ice interface. Our method was verified using full-scale debris-analog experiments and uses internal scattering within the debris layer. We use this method to measure debris thickness on Changri Nup Glacier, in the Nepal Himalaya.