The Geoid in Antarctica

An accurate definition of the geoid is severely constrained in Antarctica by the lack of gravity information, especially across the inland of the continent.

Antarctic geoid map, edition 1

Antarctic geoid map, edition 1 was produced by Bureau of Mineral Resources (now Geoscience Australia) for SCAR, in about 1980, from the GEM10C geopotentia model. Select thumbnail for larger gif_45k image of the Antarctic geoid map, edition 1 circa 1980.

Antarctic geoid map, edition 2 was produced in 1990 by AUSLIG (now Geoscience Australia) and shows the separations, in terms of the Geodetic Reference System 1980 (GRS80) ellipsoid, with 5 metre contour intervals. This edition used the OSU89A geopotential coefficients produced by Professor Rapp of Ohio State University. The program used to compute the geoid separations was provided by Dr Kearsley of the University of New South Wales. Select thumbnail for larger gif_68k image of the Antarctic geoid map, edition 2 circa 1990.

Antarctic geoid map, edition 2

The current situation with the geoid in Antarctica remains hampered by the continuing lack of ground gravity data. Although limited by the amount of data used in the Antarctic region, a grid of separation values (initially from the OSU91A geopotential model and subsequently from EGM96), was produced to allow interpolation of a separation value for any location south of 60 degrees latitude. However, the United States National Imagery & Mapping Agency (NIMA) now provides an on-line EGM96 N value service, which supersedes the previously available Geoscience Australia interpolation.

Note: The NIMA algorithm applies additional corrections to the EGM96 N values: an offset of -0.53 m to align it to the World Geodetic System 1984 (WGS84) ellipsoid and a terrain correction. This means that these files will differ from the "pure" EGM96 N values previously provided in the files for interpolation. The difference is about half a metre in an absolute sense, but will generally have little effect in a relative sense (differences in N value). Care must be used if you are working with information derived from the two different sources.

The SCAR Geoscience Standing Scientific Group is looking at future possibilities to improve the geoid in Antarctica. These include:

• The new global geoid currently being evaluated by the International Geoid Service (IGeS).
• A specifically developed geoid for the Antarctic, using enhanced gravity data and sea level connections to GPS campaign points.

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