HR: 0800h
AN: C21B-1098    [Abstracts]
TI: Crevasse detection with GPR across the Ross Ice Shelf, Antarctica
AU: * Delaney, A
EM: Allan.J.Delaney@erdc.usace.army.mil
AF: US Army ERDC, Building 4070 , Fort Wainwright, AK 99703 United States
AU: Arcone, S
EM: Steve.A.Arcone@erdc.usace.army.mil
AF: US Army ERDC, 72 Lyme Road , Hanover, NH 03755 United States
AB: We have used 400-MHz ground penetrating radar (GPR) to detect crevasses within a shear zone on the Ross Ice Shelf, 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 (<50 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 (3.0-8.0 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 geometry with the radar images. While second and third season radar profiles collected along the identical flagged route confirmed stability of the filled crevasses, those profiles also identified several new cracks opened by ice extension. Our experiments demonstrate capability of high-frequency GPR in a cold-snow environment for both defining snow layers and locating voids.
DE: 0726 Ice sheets
DE: 0728 Ice shelves
DE: 0933 Remote sensing
DE: 0994 Instruments and techniques
SC: Cryosphere [C]
MN: Fall Meeting 2005