The Allen Osborne Associates Dorne Margolin type T chokering antenna has been used extensively in the International Global Navigation Satellite System Service (IGS) tracking network for over 20 years. This antenna type, using the IGS naming convention, ''AOAD/M\_T'', was predominately installed at the original IGS sites in the late 80's, early 90's, to track signals from the Global Positioning System satellite constellation, and is still in use at operational sites today. The antenna is also used as the standard reference for relative to absolute antenna calibration conversions, which hold an important role in the history of IGS antenna calibration values. It is suspected that there may be a previously unknown subgroup of antennas that maintain a different set of phase center values which, if true, will change antenna calibration values in the IGS ANTEX file and possibly bias the International Terrestrial Reference Frame as is it currently defined.

AUSGeoid98 data files contain a 2 minute grid of AUSGeoid98 data covering the Australian region, which you can use to interpolate geoid-ellipsoid separations for the positions required.You can use your own interpolation software, or you can use Geoscience Australia's Windows Interpolation software (Winter). The data files are text files in a standard format that cover the same area as standard topographic map areas. Files covering both 1:250,000 (approximately 100 x 150 km) and 1:1,000,000 (approximately 400 x 600 km) map areas are available. There is a 4 minute overlap on all sides of each area. Data format: AUSGeoid98 data files have a header record at the start of each file, to distinguish them from the superseded AUSGeoid93 data files. AUSGeoid98 data files show the geoid-ellipsoid separation to 3 decimal places, while the superseded AUSGeoid93 data files showed only 2 decimal places. AUSGeoid98 deflections of the vertical were computed from the geoid-ellipsoid separation surface, while the AUSGeoid93 deflections of the vertical were computed from OSU91A.

GA factsheet on Interferometric Synthetic Aperture Radar (InSAR)

AUSGeoid98 is the latest in a series of national geoid models for Australia. It uses the latest available data and techniques. AUSGeoid98 consists of a 2' by 2' grid (approximately 3.6km) of geoid-ellipsoid separations (N values) relative to the GRS80 ellipsoid, which is also used for the new Geocentric Datum of Australia (GDA94). These values are suitable for use with GPS and will improve the achievable accuracy of AHD height transfer using GPS. The format of the AUSGeoid98 data files is nearly identical to the superseded AUSGeoid93 data files. Full details can be found at <a href="http://www.ga.gov.au/geodesy/ausgeoid/">AUSGeoid</a>

AUSGeoid98 data files contain a 2 minute grid of AUSGeoid98 data covering the Australian region, which you can use to interpolate geoid-ellipsoid separations for the positions required.You can use your own interpolation software, or you can use Geoscience Australia's Windows Interpolation software (Winter). The data files are text files in a standard format that cover the same area as standard topographic map areas. Files covering both 1:250,000 (approximately 100 x 150 km) and 1:1,000,000 (approximately 400 x 600 km) map areas are available. There is a 4 minute overlap on all sides of each area. Data format: AUSGeoid98 data files have a header record at the start of each file, to distinguish them from the superseded AUSGeoid93 data files. AUSGeoid98 data files show the geoid-ellipsoid separation to 3 decimal places, while the superseded AUSGeoid93 data files showed only 2 decimal places. AUSGeoid98 deflections of the vertical were computed from the geoid-ellipsoid separation surface, while the AUSGeoid93 deflections of the vertical were computed from OSU91A.

AUSGeoid98 data files contain a 2 minute grid of AUSGeoid98 data covering the Australian region, which you can use to interpolate geoid-ellipsoid separations for the positions required.You can use your own interpolation software, or you can use Geoscience Australia's Windows Interpolation software (Winter). The data files are text files in a standard format that cover the same area as standard topographic map areas. Files covering both 1:250,000 (approximately 100 x 150 km) and 1:1,000,000 (approximately 400 x 600 km) map areas are available. There is a 4 minute overlap on all sides of each area. Data format: AUSGeoid98 data files have a header record at the start of each file, to distinguish them from the superseded AUSGeoid93 data files. AUSGeoid98 data files show the geoid-ellipsoid separation to 3 decimal places, while the superseded AUSGeoid93 data files showed only 2 decimal places. AUSGeoid98 deflections of the vertical were computed from the geoid-ellipsoid separation surface, while the AUSGeoid93 deflections of the vertical were computed from OSU91A.

AUSGeoid98 data files contain a 2 minute grid of AUSGeoid98 data covering the Australian region, which you can use to interpolate geoid-ellipsoid separations for the positions required.You can use your own interpolation software, or you can use Geoscience Australia's Windows Interpolation software (Winter). The data files are text files in a standard format that cover the same area as standard topographic map areas. Files covering both 1:250,000 (approximately 100 x 150 km) and 1:1,000,000 (approximately 400 x 600 km) map areas are available. There is a 4 minute overlap on all sides of each area. Data format: AUSGeoid98 data files have a header record at the start of each file, to distinguish them from the superseded AUSGeoid93 data files. AUSGeoid98 data files show the geoid-ellipsoid separation to 3 decimal places, while the superseded AUSGeoid93 data files showed only 2 decimal places. AUSGeoid98 deflections of the vertical were computed from the geoid-ellipsoid separation surface, while the AUSGeoid93 deflections of the vertical were computed from OSU91A.

AUSGeoid98 data files contain a 2 minute grid of AUSGeoid98 data covering the Australian region, which you can use to interpolate geoid-ellipsoid separations for the positions required.You can use your own interpolation software, or you can use Geoscience Australia's Windows Interpolation software (Winter). The data files are text files in a standard format that cover the same area as standard topographic map areas. Files covering both 1:250,000 (approximately 100 x 150 km) and 1:1,000,000 (approximately 400 x 600 km) map areas are available. There is a 4 minute overlap on all sides of each area. Data format: AUSGeoid98 data files have a header record at the start of each file, to distinguish them from the superseded AUSGeoid93 data files. AUSGeoid98 data files show the geoid-ellipsoid separation to 3 decimal places, while the superseded AUSGeoid93 data files showed only 2 decimal places. AUSGeoid98 deflections of the vertical were computed from the geoid-ellipsoid separation surface, while the AUSGeoid93 deflections of the vertical were computed from OSU91A.

AUSGeoid98 data files contain a 2 minute grid of AUSGeoid98 data covering the Australian region, which you can use to interpolate geoid-ellipsoid separations for the positions required.You can use your own interpolation software, or you can use Geoscience Australia's Windows Interpolation software (Winter). The data files are text files in a standard format that cover the same area as standard topographic map areas. Files covering both 1:250,000 (approximately 100 x 150 km) and 1:1,000,000 (approximately 400 x 600 km) map areas are available. There is a 4 minute overlap on all sides of each area. Data format: AUSGeoid98 data files have a header record at the start of each file, to distinguish them from the superseded AUSGeoid93 data files. AUSGeoid98 data files show the geoid-ellipsoid separation to 3 decimal places, while the superseded AUSGeoid93 data files showed only 2 decimal places. AUSGeoid98 deflections of the vertical were computed from the geoid-ellipsoid separation surface, while the AUSGeoid93 deflections of the vertical were computed from OSU91A.

AUSGeoid98 data files contain a 2 minute grid of AUSGeoid98 data covering the Australian region, which you can use to interpolate geoid-ellipsoid separations for the positions required.You can use your own interpolation software, or you can use Geoscience Australia's Windows Interpolation software (Winter). The data files are text files in a standard format that cover the same area as standard topographic map areas. Files covering both 1:250,000 (approximately 100 x 150 km) and 1:1,000,000 (approximately 400 x 600 km) map areas are available. There is a 4 minute overlap on all sides of each area. Data format: AUSGeoid98 data files have a header record at the start of each file, to distinguish them from the superseded AUSGeoid93 data files. AUSGeoid98 data files show the geoid-ellipsoid separation to 3 decimal places, while the superseded AUSGeoid93 data files showed only 2 decimal places. AUSGeoid98 deflections of the vertical were computed from the geoid-ellipsoid separation surface, while the AUSGeoid93 deflections of the vertical were computed from OSU91A.