Connecting Land and Sea Vertical Datums: A Data Evaluation for Developing Australia’s AUSHYDROID Model

Abstract

Land and sea vertical datums have traditionally been separate reference levels, due to the different methodologies and observations used in their derivations. However, the need for a seamless connection of these datums has become important due to a wide range of applications in the coastal zone. This study evaluates existing methods, oceanographic and geodetic models and observations for the development of an operational model of coastal heights called AUSHYDROID. We use a complex study area in north west Australia to gain a new insight into how accurately the separation between the lowest astronomical tide (LAT) and a reference ellipsoid can be estimated from existing models, which could form the basis of a national AUSHYDROID model for Australia. Our results are the first attempt to use this combination of existing data in this location, suggesting that ellipsoidal heights of LAT can be estimated to an accuracy of ∼0.2 m at the coast, with the combination of DTU18MSS and FES2014b having the lowest RMS of 0.125 m. However, in some complex coastline areas such as bays and estuaries, the differences increase to >0.5 m so that additional tide gauge observations with GNSS levelling connections and improved models are needed in these regions.

Keywords:

• Tidal datum
• AUSHYDROID
• mean sea surface model
• lowest astronomical tide
• geoid
• ocean tide models
• marine chart
• coastal bathymetry

Acknowledgements

This research was performed under FrontierSI research project (FSI-4002) ‘A SCOPING STUDY AND ‘GAP’ ANALYSIS FOR THE DEVELOPMENT OF A NATIONAL HYDROID MODEL ("AUSHYDROID")’ funded by the Australian Hydrographic Office, Department of Defence.

The authors would like to both thank and acknowledge the contributions made by all FSI-4002 partners and participants involved in developing, reviewing and supporting the FrontierSI research project, including the Australian Hydrographic Office (AHO), Bureau of Meteorology (BOM), Geoscience Australia (GA), WA Department of Transport (WADOT), all of which made the research contained in this report possible. Figures 2–6 were plotted using the Generic Mapping Tools (Wessel et al. 2013).

We thank the AHO (Zarina Jayaswal, Chris Landon), WADOT (Tony Lamberto), PPA (Frans Schlack), and BOM (Andy Taylor, James Chittleborough) for providing tide gauge and GNSS data, Svetlana Erofeeva for providing the TPXO9v5 ocean tide model, and Ole Andersen for providing DTU MSS and MDT models.

FES2014 was produced by Noveltis, Legos and CLS and distributed by Aviso+, with support from CNES, and CNES-CLS. CNES-CLS MSS15 and MDT18 was obtained from Aviso+ as per Table 2.

The authors thank four anonymous reviewers and editor Dr Ron Li for their constructive comments which have helped us to improve the manuscript. We also thank Per Knudsen (DTU), Thomas Gruber (TUM) and Solène Jousset (CLS) for providing additional information on the development of the DTU and CNES-CLS MDT models.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Tide gauge data are available from the AHO, WADOT, PPA and BOM on request. AGQG2017 is available from Sten Claessens (Curtin University) on request. All other models are available as per the URL in Table 2, or by contacting the developers.

Additional information

Funding

This work was supported by The Australian Hydrographic Office, Department of Defence under Grant FSI-4002.