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Antarctic geodesy and mapping

JERRY L. MULLINS, LARRY D. HOTHEM, and CHERYL A. HALLAM, National Mapping Division, U.S. Geological Survey, Reston, Virginia 20192

The National Science Foundation (NSF), through the U.S. Geological Survey (USGS), supports geodesy and mapping in Antarctica. During the 1996-1997 season, the USGS's National Mapping Division directed its antarctic geodesy and mapping activities toward global positioning system (GPS) geodetic mapping control, topographic and satellite image mapping, and management of the Scientific Committee on Antarctic Research (SCAR) map library.

Antarctic geodetic field programs support national and international research in defining the Earth's geoid and to provide the basis for spatial reliability in mapping. Recently, the SCAR Geodesy and Geographic Information working group recommended increasing the effort to use GPS technology to tie previously obtained conventional surveys to a common Earth-centered datum. The results of this effort will provide more accurate cartographic materials better suited to the current and future satellite data-collection systems, geographic information systems, and thematic mapping programs.

In 1996, the USGS began a geodetic program to determine the relative motions of bedrock in southern Victoria Land of the Transantarctic Mountains to validate models for predicting tectonism and for improving the accuracy of models for establishing relationships to changes in global sea level and ice-sheet mass balance. Although the primary objective is monitoring vertical changes, horizontal motion will also be an important parameter. Geodetic scientists and surveyors from USGS, in cooperation with geophysicists and geologists from Byrd Polar Research Institute, Ohio State University, have established specialized monuments at up to 20 bedrock sites. Most of the sites are located between Allan Hills and an area about 150 kilometers south of the McMurdo Dry Valleys along the Transantarctic Mountains. The project is the first in a series to be performed by various investigators in future years. Accuracies at the millimeter level are the goal for the relative positions between the bedrock points. These measurements are being determined by use of late-model dual-frequency high-quality GPS receiver systems. Combined with the "precise" ephemerides provided by the International GPS for Geodynamics System (IGS), the data are being processed with the latest version(s) of appropriate software. To establish a high-level of confidence in the "base reference" measurements, a second series of measurements in the long-term project are being performed during the 1997-1998 field program. After "base reference" measurements are established within acceptable tolerances and depending on predicted magnitude of motion or initial results for possible detection of motion, repeat measurements may be at longer intervals (2 to 4 years) between GPS observing campaigns.

USGS Geodetic survey personnel, in cooperation with the University Navstar Consortium (UNAVCO), served as a focal point at McMurdo Station and vicinity and the South Pole to provide information on GPS technologies. In addition, they coordinated the establishment of a backup Continuous Operating Reference station at McMurdo, and in cooperation with Land Information New Zealand at Cape Roberts.

In April 1997, a permanent GPS continuously operating reference station (CORS) was established at Palmer Station. The system was set up to operate and collect highly accurate geodetic data similar to the operational system for the IGS station located near the RADARSAT site at McMurdo and South Pole Stations.

The United States and New Zealand undertook a joint program to combine U.S. and New Zealand geodetic networks in the McMurdo Dry Valleys area. The geodetic surveys were conducted to support U.S. and New Zealand geodetic and mapping programs. The surveys were conducted by Larry Hothem, Bill Smith, Michael Starbuck, and Vincent Belgrave using dual-frequency GPS receivers. Bedrock benchmarks were established to tie the GPS observations into the continuous-tracking GPS base station at McMurdo Station.

In January 1997, the USGS team of Bill Smith and Michael Starbuck conducted a geodetic survey using GPS receivers to establish the position of the true South Pole geodetic marker at Amundsen-Scott South Pole Station. Based on this season's observations and data from previous surveys, the team determined that the ice sheet at the South Pole continues to move to the northwest approximately 10 meters per year. The team installed a permanent brass geodetic marker identifying the 1996-1997 austral summer position.

The USGS's mapping program includes 1:50,000-scale topographic maps for areas in the McMurdo Dry Valleys. The mapping is being conducted in cooperation with the Land Information New Zealand. Under this cooperative program, the USGS obtains the aerial photographs, establishes the geodetic control, and performs the aerotriangulation. New Zealand performs the stereocompilation, collects digital cartographic data, prepares shaded relief, and provides color separates. The USGS will print the maps. The maps cover the Taylor and Wright Valleys, the Convoy Range, and Royal Society Range in the McMurdo Dry Valleys area. These 1:50,000-scale, 15-minute topographic maps have 50-meter contour intervals and 25-meter supplemental contours. The maps will be published using the World Geodetic System-84 geodetic datum. The maps will include existing and new place names approved by the U.S. Board on Geographic Names. Five maps covering part of the Royal Society Range were published in August 1993, and seven additional maps are planned for publication in 1998.

The USGS continues the USAP mapping program in Antarctica. Maps at scales ranging from 1:5,000,000 to 1:10,000, have been published as a result of this program, and many of the maps are also in digital form. Through the support of NSF, the USGS is providing access to these digital databases and assistance in their application to antarctic research projects.

The USGS has recently produced a Landsat thematic mapper (TM) satellite image map for the McMurdo Dry Valleys at 1:100,000-scale and has three combined Landsat TM and Systeme Probatoire d'Observation de la Terra (SPOT) image maps at 1:25,000-scale in the final stages of production. The maps are scheduled for publication in 1998. Four additional maps in this series are in compilation and are scheduled for publication in late 1998 or early 1999. The maps will contain U.S. Board on Geographic Names place names.

The USGS manages the SCAR library for the NSF and the U.S. Antarctic Program. The library is the official depository and distribution point for antarctic aerial photographic and cartographic products produced by the United States. The library has approximately 450,000 black-and-white and color aerial photographs of the Antarctic dating from Operation Highjump (1946-1947) through the 1989 field season. The library also houses geodetic control records, satellite images, maps, charts, and publications. Maps, charts, and publications are exchanged with nations under the provisions of the Antarctic Treaty.

The USGS continues to manage antarctic geographic names using the computer-based geographic names information system and has recently made the names available through the USGS geographic names World Wide Web site.

These programs were funded by National Science Foundation grant OPP 91-14787.