HR: 09:00h
AN: C41D-05    [Abstracts]
TI: Ice Thickness and Basal Topography Near the Ross/Amundsen Ice Divide Revealed by Ground-based Radar and New Signal Processing
AU: * MacGregor, J A
EM: joemac@u.washington.edu
AF: Unversity of Washington Earth & Space Sciences, Box 351310, Seattle, WA 98195 United States
AU: Winebrenner, D P
EM: dpw@apl.washington.edu
AF: University of Washington Applied Physics Lab, Box 355640, Seattle, WA 98195 United States
AU: Conway, H
EM: conway@ess.washington.edu
AF: Unversity of Washington Earth & Space Sciences, Box 351310, Seattle, WA 98195 United States
AU: Sylvester, J
EM: sylvest@math.washington.edu
AF: University of Washington Dept. of Mathematics, Box 354350, Seattle, WA 98195 United States
AB: The U.S. Science Plan for Deep Ice Coring in West Antarctica calls for a new ice core from a site near the Ross Sea/Amundsen Sea ice divide. The region is attractive because very thick ice in the region promises recovery of a long climate record with relatively high time resolution during the last glacial period. Ice thickness (together with accumulation rate history) is needed to estimate depth-age relationships for candidate core sites. However bed echoes from both airborne (Morse et al., Ann. Glac., v 35, 2002) and our ground-based radar profiles are often faint or not detected, especially in regions of very thick ice (up to 3500 m) that are preferred for potential core sites. Here we apply a combination of matched filtering and lateral averaging, which improves the signal-to-noise ratio of both englacial and bed echoes, to our 1.0 and 1.5MHz ground-based radar data collected in the vicinity of the western divide. Matched filtering requires a reflector model, which we derive from a strong, deep radar layer that is observed in nearly all transects. The signal model is consistent with bed echoes at sparse locations where the latter are reliable. Lateral averaging consists of coherent averaging at each point in the echogram, along lines of several slopes, followed by selection of the average of largest magnitude (constrained by an estimate of the maximum reflector slope). Lateral averaging is analogous to performing more stacking during acquisition to reveal fainter reflectors. Compared with data that have been processed by previous standard methods (eg. Gades et al., J. Glac. v 46, 2000), the new processing improves detection of the bed. Of particular interest is a profile along a flow line that crosses the ice divide at 42 km. The new processing clearly illuminates the bed at candidate site E at 15 km on the Ross Sea side of the divide; ice thickness there is 3460m. The bedrock divide is displaced 8 km west from the ice divide. No additional englacial layers were revealed by the processing in this case, and the deep radar stratigraphy is consistent with that found in a 1.5MHz transect that intersects the Byrd core. The basal topography near Site E is rough on the scale of 2-3km but the bed reflector itself is fairly coherent.
DE: 9310 Antarctica
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting