Iceberg B15a  |
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| The primary problem with sounding thin-floating ice, such as ice shelves
and icebergs 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, we collected 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 (pictured on left and right). 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. The figure is a de-chirped “south” profile that shows multiple echoes from the bergs top and bottom surfaces. |
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| These images were included in a presentation given by Blankenship and others at the Sept., 2002 WAIS meeting in Algonkin, Va. Look for a new and improved interpretation in a presentation at Fall AGU, 2002 |