South Pacific Sea Level & Climate Monitoring (SPSLCMP)

An introduction to this project can be found on the South Pacific Sea Level and Climate Monitoring Project (SPSLCMP) web site.

A significant new component of the project in Phase III, which began in 2001, is the GPS geodetic component, undertaken by Geoscience Australia.

Need for the Geodetic Component for Absolute Sea Level Monitoring

Tide gauge records collected over long periods indicate a rise in global sea level of 10-30 cm over the past century. However, there are large discrepancies in the rates of change of sea level indicated by different tide gauges, or groups of tide gauges spanning particular regions. These differences are considered to be largely caused by vertical land motion resulting from phenomena such as glacial rebound, tectono-physics, subsurface fluid withdrawal and sediment consolidation.

In order to decipher the signals observed by a network of tide gauges from vertical crustal movement so that absolute sea level changes could be monitored, it is necessary to establish the absolute positions (heights) of the tide gauges in an accurate, global, geocentric terrestrial reference frame. Currently, the International Terrestrial Reference Frame 2005 (ITRF2005) is used.

Measurements of vertical crustal movement together with the establishment of benchmark tide gauges in this global geocentric reference frame will satisfy some fundamental aims. It will lead to the establishment of a world vertical datum, by providing the means to accurately connect national, continental and international vertical datums. This will provide the means to estimate past and current rates of change in global mean sea level.

In view of the current debate that sea level changes may be related to global warming as pollution intensifies the greenhouse effect, these measurements will lead to a better understanding of the causes that may accelerate this change in mean sea level. Since changes in sea level average about one to three millimetres per annum, any vertical motion of the crust must be monitored at this level of accuracy, and within short time spans of five to 10 years.

In addition, the geodetic component for monitoring absolute sea level changes requires a local network of benchmarks and reference marks that are re-surveyed regularly by Terrestrial Methods or Global Positioning Systems (GPS). Reference Mark Monitoring Report

The geodetic component comprises a Continuous Global Positioning System (CGPS) network which will provide long term height time series.

The CGPS geodetic outputs for the SPSLCMP are:

• Long term height time series;
• (in a) Consistent accurate global geocentric terrestrial reference frame - ITRF2005;
• Accuracy requirements - the uncertainty of the determination of the long term secular trend (in height component) should be at least consistent with the expected sea level rise determined from tide gauge measurements over the last century - 1mm/annum;
• Computational standards that are consistent with the International Earth Rotation Service (IERS) 2003 conventions.

Project Links

• The Bureau of Meteorology National Tidal Centre (NTC)
• Project Enquiries should be directed to spslcmp@bom.gov.au