Detecting supraglacial debris thickness with GPR under suboptimal conditions

• Published in: Journal of Glaciology
• Main Authors: Alexandra Giese, Steven Arcone, Robert Hawley, Gabriel Lewis, Patrick Wagnon
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press 2021
• Subjects: Debris-covered glaciers; glacier geophysics; glaciological instruments and methods; ground-penetrating radar; supraglacial debris; Environmental sciences; GE1-350; Meteorology. Climatology; QC851-999; Journal of Glaciology
• Online Access: https://doi.org/10.1017/jog.2021.59; https://doaj.org/article/6a6cf822fcf54a749a305349a9ce30e8

The thickness of a supraglacial layer is critical to the magnitude and time frame of glacier melt. Field-based, short pulse, ground-penetrating radar (GPR) has successfully measured debris thickness during a glacier's melt season, when there is a strong return from the ice–debris interface, but profiling with GPR in the absence of a highly reflective ice interface has not been explored. We investigated the performance of 960 MHz signals over 2 km of transects on Changri Nup Glacier, Nepal, during the post-monsoon. We also performed laboratory experiments to interpret the field data and investigate electromagnetic wave propagation into dry rocky debris. Laboratory tests confirmed wave penetration into the glacier ice and suggest that the ice–debris interface return was missing in field data because of a weak dielectric contrast between solid ice and porous dry debris. We developed a new method to estimate debris thicknesses by applying a statistical approach to volumetric backscatter, and our backscatter-based calculated thickness retrievals gave reasonable agreement with debris depths measured manually in the field (10–40 cm). We conclude that, when melt season profiling is not an option, a remote system near 1 GHz could allow dry debris thickness to be estimated based on volumetric backscatter.