We have used 400-MHz ground penetrating radar (GPR) to detect crevasses within a shear zone on the Ross Ice Shcelf, Antarctica, to support traverse operations. The transducer was attached to a 6.5-m boom and pushed ahead of an enclosed tracked vehicle. Profile speeds of 4.8-11.3 km / hr allowed real- time crevasse image display and a quick, safe stop when required. Thirty-two crevasses were located with radar along the 4.8 km crossing. Generally, crevasse radar images were characterized by dipping reflections above the voids, high-amplitude reflections originating from ice layers at the base of the snow-bridges, and slanting, diffracting reflections from near-vertical crevasse walls. New cracks and narrow crevasses (40 cm width) show no distinct snow bridge structure, few diffractions, and a distinct band where pulse reflections are absent. Wide (0.5-5.0 m), vertical wall crevasses show distinct dipping snow bridge layering and intense diffractions from ice layers near the base of the snow bridge. Pulse reflections are absent from voids beneath the snow bridges. Old, wide (3.W.O m) and complexly shaped crevasses show well-developed, broad, dipping snow-bridge layers and a high-amplitude, complex, diffraction pattern. The crevasse mitigation process, which included hot-water drilling, destroying the bridges with dynamite, and back-filling with bulldozed snow, afforded an opportunity to ground-truth GPR interpretations by comparing void size and snow-bridge geametry with the radar images. Second season radar profiles colllected along the identical flagged route confirmed stability of the filled crevasses and identified eight new cracks opened by ice extension. Our experiment demonstrates the utility and reliability of real-time crevasse detection with GPR. Keywords-crevasse, snow stratigraphy, ground penetrating radar, traverse, McMurdo shear zone

Crevasse detection with GPR across the Ross Ice Shelf, Antarctica

Robotics in Snow and Ice

. 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.

/pdf/the-response-of-supraglacial-debris-to-elevated-high-zicn63oyz5.pdf

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

Definition: The terms"robotics in snow and ice"refers to robotic systems being studied, developed, and used in areas where water can be found in its solid state. This specialized branch of field robotics investigates the impact of extreme conditions related to cold environments on autonomous vehicles.

To quantify the ablation processes on a debris covered glacier, a simple distributed ablation model has been developed and applied to a selected glacier. For this purpose, a set of field measurements was carried out to collect empirical data. A morphometric analysis of the glacier surface enables us to capture statistically the areal distribution of topographic features that influence debris thickness and consequently ablation. Remote-sensing techniques, using high-resolution satellite imagery, were used to extrapolate the in situ point measurements to the whole ablation area and to map and classify melt-relevant surface types. As a result, a practically applicable method is presented that allows the estimation of ablation on a debris covered glacier by combining field data and remote-sensing information. The sub-debris ice ablation accounts for about 24% of the entire ice ablation, while the percentage of the moraine covered area accounts for approximately 32% of the entire glacierized area. Although the ice cliffs occupy only 1.7% of the debris covered area, the melt amount accounts for approximately 12% of the total sub-debris ablation and 2.5% of the total ablation respectively. Our study highlights the influence of debris cover on the response of the glacier terminus in a particular climate setting. Due to the fact that melt rates beyond 0.1m of moraine cover are highly restricted, the shielding effect of the debris cover dominates over the temperature and elevation dependence of the ablation in the bare ice case.

Impact of varying debris cover thickness on ablation: a case study for Koxkar Glacier in the Tien Shan (SCI)

Velocity field in the McMurdo shear zone from annual ground penetrating radar imaging and crevasse matching

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Velocity field in the McMurdo shear zone from annual ground penetrating radar imaging and crevasse matching

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