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Support Office for Aerogeophysical Research (SOAR): West antarctic field activities (1994-1996)

Thomas G. Richter, Jeffrey L. Williams, and Donald D. Blankenship, Institute for Geophysics, University of Texas, Austin, Texas 78759

Robin E. Bell, Lamont-Doherty Earth Observatory, Palisades, New York 10964

Airborne research platforms are well suited to the study of Earth processes in remote regions. The mission of the Support Office for Aerogeophysical Research (SOAR), a facility of the National Science Foundation's Office of Polar Programs (NSF/OPP), is to make airborne geophysical observations available to the broad research community of geology, glaciology, and other sciences. The Institute for Geophysics at the University of Texas at Austin, Lamont-Doherty Earth Observatory of Columbia University, and the Geophysics Branch of the U.S. Geological Survey have the major responsibilities for SOAR. SOAR's central offices are located in Austin, Texas.

SOAR was chartered by a cooperative agreement between the National Science Foundation and the University of Texas at Austin. The facility goal is to develop, maintain, and operate a suite of geophysical systems aboard a Twin Otter aircraft for research in Antarctica. Much of the equipment, staff, and experience for SOAR were drawn from the Corridor Aerogeophysics of the Eastern Ross Transect Zone (CASERTZ) science project which developed this capability for the Twin Otter (Behrendt et al. 1994; Bell et al. 1993, pp. 571-577; Blankenship et al. 1993; Brozena et al. 1993).

The SOAR research aircraft provides a unique platform for the simultaneous collection of geophysical and navigation data. The geophysical instrumentation includes a gravimeter, magnetometer, laser altimeter, and ice-penetrating radar. The positioning instrumentation consists of single-frequency global positioning system (GPS) receivers for navigation, dual-frequency GPS receivers for postprocessed positioning (allowing differential carrier phase positioning), an inertial navigation system for aircraft attitude, and a precision pressure altimeter (table). The survey aircraft is a De Havilland DHC-6 Twin Otter modified to accommodate the geophysical and navigational equipment. The most visible modifications are large wing-mounted radar antennas below the wings and the towed magnetometer sensor "bird" stowed below the aft fuselage ( figure 1).

Along with the hardware suite, robust data-acquisition and quality-control systems have been developed by SOAR. Measurements from each geophysical system are tagged with GPS time and recorded to disk. Continuous GPS positioning data are collected independently of the main acquisition system throughout each flight. Ground-based instrumentation collects magnetics observations and information on the GPS constellation. Data from each flight are downloaded and quality checked within a few hours of landing, allowing detection and correction of equipment malfunctions with minimal disruption to the survey schedule.

As an NSF facility, SOAR's fundamental goal is to meet the experimental objectives of its client science projects. Presently, SOAR has two clients working under separate proposals: a collaborative West Antarctic Ice Sheet Project and the University of Wisconsin-Madison. The science objectives of these researchers require SOAR to complete an aerogeophysical survey of a 200,000-square-kilometer region with an orthogonal survey grid and a 5.3-kilometer line spacing. This work started during the 1994-1995 antarctic summer field season and will be completed in the 1996-1997 season. Ultimately, three adjacent regions are to be covered ( figure 2):

For the 1994-1995 and 1995-1996 seasons, SOAR was based at Byrd Surface Camp. During these two seasons, the surveys of the BSB and WAZ were completed with a total of 120 survey flights gathering 67,000 line-kilometers of data. During its first field season, SOAR completed 32 survey flights in BSB. The second season (1995-1996) was much more ambitious, and 88 survey flights were completed. For 1995-1996, the sustainable rate for typical 4-hour survey flights was 2.5 to 3.0 flights per day with approximately 1 day of bad weather every 3 days. During this season, SOAR maintained around-the-clock flight operations with one scheduled break per day to avoid collecting magnetics data during the worst of the diurnal geomagnetic field instabilities. GPS satellite visibility was good all of the time and did not pose a constraint on flight scheduling. For 1996-1997, the SOAR base-of-operations will be Siple Dome Camp. Seventy-two survey flights are planned to complete the West Antarctic Ice Sheet and University of Wisconsin Projects.

Following each field season, the data for the year are organized and distributed to the client investigators. Currently, the data provided are raw, unprocessed instrument readings with time stamps. Starting with the 1997-1998 field season, SOAR will begin to provide various levels of processed products.

The SOAR facility has large and diverse logistical requirements and was assisted by individuals and organizations in its field preparations and deployments. Operation and maintenance of the Twin Otter survey aircraft were provided by Kenn Borek Air, Ltd., through a contractual agreement managed by Antarctic Support Associates (ASA). ASA and the Naval Support Force Antarctica (NSFA) provided on-site management and support at Byrd Surface Camp. The Bell BGM-3 airborne gravimeter was on loan from the Naval Oceanographic Office. GPS receivers were supplied by the University Navigation Consortium (UNAVCO) and the National Aeronautics and Space Administration. Cargo support was provided by a number of groups and was coordinated by Lee Degalen for the NSF at Port Hueneme, California. SOAR would like to recognize the invaluable contributions to its success by these persons and organizations.

The Support Office for Aerogeophysical Research is funded by the National Science Foundation under Cooperative Agreement OPP 91-19379.

References

Behrendt, J.C., D.D. Blankenship, C.A. Finn, R.E. Bell, R. Sweeney, S.M. Hodge, and J.M. Brozena. 1994. CASERTZ aergeomagnetic data reveal late Cenozoic flood basalts(?) in the west antarctic rift system. Geology, 22(6), 527-530.

Bell, R.E., B.J. Coakley, D.D. Blankenship, S.M. Hodge, J.M. Brozena, and J. Jarvis. 1993. Airborne gravity from a light aircraft: CASERTZ 1990-91. In Y. Yoshida, K. Kaminuma, S. Shiraishi (Eds.), Recent progress in antarctic earth science. Tokyo: Terra Scientific.

Blankenship, D.D., R.E. Bell, S.M. Hodge, J.M. Brozena, J.C. Behrendt, and C.A. Finn. 1993. Active volcanism beneath the west antarctic ice sheet and implications for ice-sheet stability. Nature, 361, 526-529.

Brozena, J.M., J.L. Jarvis, R.E. Bell, D.D. Blankenship, S.M. Hodge, and J.C. Behrendt. 1993. CASERTZ 1991-1992: Airborne gravity and surface topography measurement. Antarctic Journal of the U.S., 28(5), 1-3.