1. AUSGeoid Richard Bean Robyn Stevens 26 May 2010

2. 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

3. Geoid/ellipsoid separation (N)

4. Australian Height Datum Mainland Australia: 5 May 1971 (AHD71) –MSL for 30 Tide stations 1966-1968 Tasmania: 17 October 1983 –MSL at Hobart and Burnie 1972

5. Why MSL?

7. Global Geopotential Models OSU89A OSU91A – Resolution 55km EGM96 - Resolution 55km EGM2008 – Resolution 9km

8. 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

9. Geoid In Antarctica Antarctic geoid map, edition 2

11. 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

12. Gravimetric component of AusGeoid09 (satellite gravity observations plus 1.3 million points from GA’s land gravity database) OFFSET: O = h – Nag – Hahd

14. References www.ga.gov.au 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): 30- 40 Johnstone,GM., Featherstone, W.E. (1998) Ausgeoid 98: A New Gravimetric Geoid For Australia.