A Re-Evaluation of the Offset in the Australian Height Datum Between Mainland Australia and Tasmania

Abstract

The adoption of local mean sea level (MSL) at multiple tide-gauges as a zero reference level for the Australian Height Datum (AHD) has resulted in a spatially variable offset between the geoid and the AHD. This is caused primarily by sea surface topography (SSTop), which has also resulted in the AHD on the mainland being offset vertically from the AHD on the island of Tasmania. Errors in MSL observations at the 32 tide-gauges used in the AHD and the temporal bias caused by MSL observations over different time epochs also contribute to the offset, which previous studies estimate to be between ∼+100 mm and ∼+400 mm (AHD on the mainland above the AHD on Tasmania). This study uses five SSTop models (SSTMs), as well as GNSS and two gravimetric quasigeoid models, at tide-gauges/tide-gauge benchmarks to re-estimate the AHD offset, with the re-evaluated offset between −61 mm and +48 mm. Adopting the more reliable CARS2006 oceanographic-only SSTM, the offset is −12 ± 11 mm, an order of magnitude less than three previous studies that used geodetic data alone. This suggests that oceanographically derived SSTMs should be considered as a viable alternative to geodetic-only techniques when attempting to unify local vertical datums.

Keywords:

• AHD
• mean sea level
• sea surface topography modeling
• vertical datum unification

Acknowledgements

Mick Filmer received financial support from an Australian Postgraduate Award, Curtin University's The Institute for Geoscience Research (TIGeR) and the CRC for Spatial Information. Will Featherstone was the recipient of an Australian Research Council Professorial Fellowship (project number DP0663020). The views expressed herein are those of the authors and are not necessarily those of the ARC or the CRC for Spatial Information. We would like to thank Geoscience Australia for supplying the GNSS dataset and Dr. Xiaoli Deng (University of Newcastle) for supplying us with CARS2006 (data originally from CSIRO Marine Laboratories), and Rio05 (AVISO). We also acknowledge DNSC (DNSC08 MDT), NASA/JPL (JPL08, GGM02 DOT), and NGA (EGM2008) for their freely available datasets. We would also like to thank the three anonymous reviewers and editor for their comments on this manuscript. This is TIGeR publication number 385.