The Stability of Tide Gauges in the South Pacific Determined from Multiepoch Geodetic Levelling, 1992 to 2010

Abstract

Tide gauge data is important for determining global or local sea level rise with respect to a global geocentric reference frame. Data from repeated precise levelling connections between the tide gauges and a series of coastal and inland benchmarks, including Continuous GPS (CGPS) benchmarks, are used to determine the stability of tide gauges at 12 locations in the South Pacific. The method for determining this stability is based on a constant velocity model which minimises the net movement amongst a set of datum benchmarks surveyed since the installation of the tide gauges. When assessed at a 95% confidence interval, and with the exception of the Solomon Islands, none of the tide gauges were found to be in motion relative to their CGPS benchmarks. The Solomon Islands estimate is considered to be unreliable since the CGPS benchmark was recently established and has been surveyed fewer than three times. In Tonga and Cook Islands, the tide gauges were found to be disturbed or affected by survey errors whereas the Vanuatu results were affected by earthquakes.

Keywords:

• Precise levelling
• vertical velocity
• inner constraint adjustment
• deformation monitoring
• sea level monitoring

Acknowledgements

The second author publishes with the permission of the Chief Executive Officer, Geoscience Australia (GA). The comments and suggestions by Dr John Dawson are most valued. This study made use of levelling data collected collaboratively by staff of GA, National Tidal Facility, Australia (NTF) and Secretariat of the Pacific Community (SOPAC) with funding from AusAID. The authors thank the survey team including Steven Turner, Brian Ratcliff, Bob Twilley, Steve Yates, Andrick Lal, Nick Brown, and Guorong Hu.