Noise and Periodic Terms in the EPN Time Series
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The EUREF Permanent Network (EPN) has been installed in 1996 with some 30 stations and now includes more than 190 permanent GNSS sites (see Fig. 1). The network is operated according to the standards of the International GNSS Service (IGS) and it is considered as a regional densification of the ITRF (International Terrestrial Reference Frame). The EPN is primarily a geodetic reference network, but its results are also widely used for geophysical studies. In order to better serve the user needs, the EUREF Time Series Analysis special project monitors the weekly combined SINEX solutions, cleans the individual station coordinate series, and maintains and publishes the database of the detected coordinate offsets and outliers. Using this info, cleaned cumulative solutions are then computed with the CATREF software (Altamimi et al 2004). The estimated coordinates and velocities, together with the outlier and offset database are regularly updated and published on the EPN CB website (www.epncb.oma.be ).
In this study we focus on the noise and harmonic analysis of the EPN coordinate series. The analysis is done with the CATS software (Williams SD, Proudman Oceanographic Laboratory), which uses a MLE (Maximum Likelihood Estimator) to determine the noise characteristic and seasonal variation of the coordinate time series. The EPN weekly SINEX files from GPS week 860 to 1385 are involved in the computations.
We proved the presence of the colored noise in the EPN time series. The harmonic analysis showed moderate seasonal amplitudes. The phase lag distribution for the horizontal components are not random, well determined phase lag values were found. The Up component shows a more diffuse phase lag distribution. The physical reality of the phase lag values are not discussed here.
Keywordsreference network EUREF, time series analysis annual periodicity noise analysis
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