The European Sea Level Service (ESEAS): The Continuous GPS Coordinate Time Series Analysis Strategy

The European Sea Level Service (ESEAS) was established in June 2001 and has the objective to provide sea-level and sea-level related information for the European waters to scientific and non-scientific users both from inside and outside Europe. The ESEAS-RI (Research Infrastructure) commenced its work in November 2002 for a three year period, included 25 institutions from 17 countries and aims to provide substantial resources to ESEAS for improving the observational network as well as the tools for exploitation of the data. Within ESEAS-RI, data from continuous GPS (CGPS) stations co-located with tide gauges in Europe are analyzed and vertical station velocity estimates at the 1 mm/yr accuracy level with uncertainties of < 0.5 mm/yr are envisaged. Therefore, an ESEAS CGPS coordinate time series analysis strategy was developed in order to separate real geophysical signals from the underlying noise. Coordinate time series pre-processing identifies outliers and discontinuities in the time series. The following parameterization includes a mean value, a constant rate, periodic terms with annual and semi-annual frequencies, and offset magnitudes for the identified discontinuities. Maximum Likelihood Estimation then determines all parameters plus the magnitudes of different stochastic noise. Empirical Orthogonal Function (EOF) analysis allows the discrimination between local, station-specific, deterministic processes and inter-station, correlated transient signals, i.e. common mode errors. Using the common mode errors from the EOF analysis, the coordinate time series of the continuous and eventually also campaign data from the ESEAS GPS network are filtered and improved. After outlining the ESEAS CGPS coordinate time series analysis strategy this presentation shows initial results for coordinate time series from a selection of CGPS stations in Europe for a four year (2000-2003) test period.