Back to list of UTIG presentations at Fall Agu

D.D. Blankenship, D.L. Morse and J.W. Holt

Understanding the migration and disintegration of large tabular icebergs requires knowledge of their thickness and basal character as well as the distribution of vertical fractures originating at both the surface and the base. An efficient method for making these observations is with an airborne ice-penetrating radar. The primary problem with these radar measurements is the large system sensitivity required to observe simultaneously large-amplitude reflections from the ice-ocean interface and the more subtle high-resolution signals from near-surface scatterers and englacial layering.

During the 2001/2002 austral summer, the University of Texas was field testing an experimental radar sounder (developed in collaboration with the Jet Propulsion Laboratory) mounted on a twin-engine aircraft operating from the Ice Runway at McMurdo Station. With this system, which was designed specifically to optimize both resolution and sensitivity, we performed phase-coherent radar imaging along four profiles over iceberg B15a which, at that point in time, was lying nearly perpendicular to the front of the Ross Ice Shelf abutting Ross Island. One 140 km profile parallels and lies within about 10 km of the fresh shelf break while an adjacent 160 km profile bisects the iceberg. These two profiles are connected by two shorter profiles (approximately 35 and 45 km) running perpendicular from the fresh shelf break all the way to the former shelf edge. Along its centerline (parallel to the former shelf edge) B15a ranges from about 200 to 270 m in thickness. In the shorter perpendicular lines the ice thickness thins rapidly to less than 100 m as the former shelf edge is approached. Our objective of simultaneously imaging high-resolution surface and bottom scatterers as well as the extremely subtle englacial layering was also achieved.