Search

n this study we present results from a recent reprocessing effort that included data from more than 120 continuous Global Positioning System (CGPS) stations in the British Isles for the period from 1997 to 2008. Not only was the CGPS network dramatically densified from previous investigations by the authors, it now also includes, for the first time, stations in Northern Ireland, providing new constraints on glacio-isostatic processes active in the region. In our processing strategy we apply a combination of re-analysed satellite orbit and Earth rotation products together with updated models for absolute satellite and receiver antenna phase centers, and for the computation of atmospheric delays. Our reference frame implementation uses a semi-global network of 37 stations, to align our daily position estimates, using a minimal constraints approach, to ITRF2005. This network uses a combination of current IGS reference frame stations plus additional IGS stations in order to provide similar network geometries throughout the complete time span. The derived horizontal and vertical station velocities are used to investigate present-day crustal/land motions in the British Isles. This first solution provides the basis for our contri- bution to the Working Group on Regional Dense Velocity Fields, 2007 - 2011 of the International Asso- ciation of Geodesy Subcommission 1.3 on Regional Reference Frames.

Researchers studying climate change have used historical tide gauge measurements from all over the world to investigate the changes in sea level that have occurred over the last century or so. However, such estimates are a combination of any true sea level variations and any changes in ground level at the specific tide gauge. For a tide gauge record to be used to determine the climate related changes in sea level it is necessary to correct for any changes in ground level. The development in geodetic techniques for monitoring changes in ground level at British tide gauges has been on-going at the IESSG and POL since 1990, based on research funded by both Defra and the Environment Agency. Since 1996, this research has focused on the establishment of continuous GPS (CGPS) stations and the use of absolute gravity (AG), as independent geodetic techniques for measuring changes in ground level. This paper details the results of Defra/EA R&D project FD2319, which is part of the Risk Evaluation and Understanding of Uncertainty Theme. The paper shows how CGPS and AG have been used on a national scale to monitor changes in ground level at tide gauges and obtain estimates of changes in sea level, decoupled from changes in ground level.