HR: 14:55h
AN: U23C-06    [Abstracts]
TI: Airborne Radar Sounding: A Survey of the Thwaites Glacier Catchment of the Amundsen Sea Embayment, West Antarctica
AU: * Peters, M E
EM: mattp@ig.utexas.edu
AF: The University of Texas Institute for Geophysics Jackson School for Geosciences, 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759 United States
AU: Blankenship, D D
EM: blank@ig.utexas.edu
AF: The University of Texas Institute for Geophysics Jackson School for Geosciences, 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759 United States
AU: Holt, J W
EM: jack@ig.utexas.edu
AF: The University of Texas Institute for Geophysics Jackson School for Geosciences, 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759 United States
AU: Morse, D L
EM: morse@ig.utexas.edu
AF: The University of Texas Institute for Geophysics Jackson School for Geosciences, 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759 United States
AU: Young, D A
EM: duncan@ig.utexas.edu
AF: The University of Texas Institute for Geophysics Jackson School for Geosciences, 4412 Spicewood Springs Rd. Bldg. 600, Austin, TX 78759 United States
AB: Radar sounding is an established technique for investigating subsurface structure and is capable of regional scale surveys. It is particularly well-suited for penetrating ice masses with radars operating up through the very high frequency (VHF) range. Ice-sounding radar primarily reveals the thickness and underlying morphology of Earth's ice sheets and glaciers. These observations are necessary for understanding the ice mass balance and its effect on sea-level change. Also, radar sounding can be used to observe layers within the ice and to characterize the subglacial interface. The West Antarctic Ice Sheet is a marine ice sheet of which 75% is resting on bedrock below sea level. This situation is highly unstable and as the climate warms, the potential for rapid discharge of the ice sheet grows. Examining the areas of the ice sheet that are most likely to react to changing climate is essential. The Amundsen Sea Embayment contains two of the most important outlet glaciers in West Antarctica: Thwaites and Pine Island Glaciers. These two glaciers have among the highest discharge velocities in West Antarctica and they lack large protective ice shelves, making them susceptible to warming ocean waters. The area is currently a target of interest for both the GRACE and GLAS satellite missions, as well as future land- and air-based surveys. The UT Institute for Geophysics maintains and operates the High-Capability Radar Sounder (HICARS) system. The HICARS system was configured to operate in chirped pulse mode with a 60 MHz center frequency, 15 MHz bandwidth, and 1 microsecond pulse width. Peak transmit power was about 8000 watts. The two-channel variable-gain receiver down-converts the signals to a center frequency of 10 MHz. These signals were coherently sampled at 50 MHz for a record length of 64 microseconds. High and low-gain channels were configured to record a wide dynamic range of echoes simultaneously and without range-dependent gain control (e.g., strong surface echoes and weak bed echoes without clipping). Data acquisition included coherent integrations of 32 returned radar signals yielding observations about every 35 cm along-track. Pulse compression and synthetic aperture radar (SAR) processing were components of data analysis. During the 2004/05 Antarctic field season, the University of Texas (UT) and the British Antarctic Survey (BAS) completed the first extensive aerogeophysical survey of the ASE glacial drainage basins. The UT portion of the survey acquired roughly 43,500 line-km of data on a 15 km grid covering the Thwaites Glacier catchment. The survey was flown from a de Havilland DHC-6 Twin Otter aircraft and included ice-sounding radar, laser altimetry, gravity and magnetics measurements, and GPS positioning. The radar data over the Thwaites Glacier catchment have been processed to determine the surface and subglacial elevations, and the results significantly extend previous knowledge in this critical region. Much of the subglacial interface lies below sea level, and a broad coastal sill bounds an extensive interior basin beneath the Thwaites Glacier, which is fed by broad deep drainage channels. The relatively high ground of the Marie Byrd Land volcanic province to the west of Thwaites Glacier is deeply incised, and the radar data reveal edifices beneath the ice surface. Radar echo analysis also reveals fine-scale roughness and character of the subglacial interface.
DE: 0762 Mass balance (1218, 1223)
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 9310 Antarctica (4207)
DE: 9805 Instruments useful in three or more fields
SC: Union [U]
MN: Fall Meeting 2005