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CGPS coordinate time series analysis strategy was evaluated to determine highly accurate vertical station velocity estimates with realistic uncertainties. This strategy uses a combination of techniques to (1) obtain the most accurate parameter estimates of the station motion model, (2) infer the stochastic properties of the time series in order to compute more realistic error bounds for all parameter estimates, and (3) improve the understanding of apparent common systematic variations in the CGPS coordinate time series, which are believed to be of geophysical and/or technical origin. The strategy provided a pre-processing of the coordinate time series in which outliers and discontinuities were identified. Subsequent parameterization included a mean value, a constant rate, periodic terms with annual and semi-annual frequencies, and offset magnitudes for identified discontinuities. All parameters plus the magnitudes of different stochastic noise were determined using maximum likelihood estimation (MLE). Empirical orthogonal function (EOF) analysis was used to study both the temporal and spatial variability of the common modes determined by this technique. After outlining the CGPS coordinate time series analysis strategy this paper shows initial results for coordinate time series for a four year (2000–2003) period from a selection of CGPS stations in Europe that are part of the European Sea Level Service (ESEAS) CGPS network

Recently the concept of using dual-continuous GPS (dual-CGPS) stations for monitoring vertical land movements at tide gauge sites was proposed by a working group of the European Sea Level Observing System (EOSS). In this concept, one CGPS station is established at the tide gauge, in order to monitor the local vertical land movements, and a second CGPS station is established on stable rock, within a few kilometers of the tide gauge further inland. Since 1997, a network of CGPS stations has been established to monitor vertical land movements in the UK. For the dual-CGPS station concept, pairs formed by the CGPS stations at Newlyn tide gauge and Camborne and at Lowestoft tide gauge and Hemsby, have been analyzed over a time span of approximately 2.7 and 2.0 years respectively. It has been shown by numerous authors that temporal and spatial correlations in CGPS coordinate time series can introduce biases in the estimated station velocities and their uncertainties. By analyzing the coordinate time series of two CGPS stations close to each other, spatial correlations can be removed successfully by differencing and a cleaner, difference time series for each coordinate component can be obtained. In this paper, the observed coordinate time series of four CGPS stations have been used to produce synthetic coordinate time series of 6 years in length. Station velocities and their uncertainties have been derived for both observed and synthetic coordinate time series and compared in order to assess the capabilities of the dual-CGPS concept to better describe local and geophysical vertical land movements.