AUSGeoid Richard Bean Robyn Stevens 26 May 2010
Geoid 3D surface of equal gravity (Equipotential) Not smooth like an ellipsoid Transformation needed to convert between ellipsoid and Geoid Geoid approximates Mean Sea Level
Geoid/ellipsoid separation (N)
Australian Height Datum Mainland Australia: 5 May 1971 (AHD71) –MSL for 30 Tide stations Tasmania: 17 October 1983 –MSL at Hobart and Burnie 1972
Why MSL?
Global Geopotential Models OSU89A OSU91A – Resolution 55km EGM96 - Resolution 55km EGM2008 – Resolution 9km
AUSGeoid – History AUSGeoid91 –OSU89A global model –10’ x 10’ grid (20km) ± 1-2m –1980 AGSO gravity database –GRS80 Reference Ellipsoid AUSGeoid93 –-OSU91A AUSGeoid98 (Current Model) –EGM96 global geopotential model –2’ x 2’ grid (3.6km) +-50cm –GRS80 Reference Ellipsoid AUSGeoid09 –EGM2008 – 2km grid 5cm accuracy
Geoid In Antarctica Antarctic geoid map, edition 2
The FUTURE for the Australian Geoid? Due for release mid 2010 Errors due to North/South water density difference are removed –AHD approx 50cm above the Geoid in North –50cm below in the South Accuracy of ± 5cm AUSGeoid09
Gravimetric component of AusGeoid09 (satellite gravity observations plus 1.3 million points from GA’s land gravity database) OFFSET: O = h – Nag – Hahd
References AUSGEO News, Issue 97, March 2010 Kearsley, A.H.W., Govind, R. (1991) Geoid evaluation in Australia: a status report. The Australian Surveyor, 36(1): Johnstone,GM., Featherstone, W.E. (1998) Ausgeoid 98: A New Gravimetric Geoid For Australia.