Exploring the common mode error: case study of Europe

The Global Navigation Satellite Systems (GNSSs) have the invaluable ability to monitor the crustal deformation either for geodesy (determination of the shape of the Earth) or for geophysics (interpretation of geodynamical processes). However, these systems have some limitations. Among the others, the systematic errors and unmodelled effects defined and observed as a common mode error (CME) have to be mentioned. Isolation of CME from displacements seems to be crucial for obtaining reliable velocities and their uncertainties. In this research we use a set of European GPS-derived vertical displacements recorded at 4443 permanent stations provided by the Nevada Geodetic Laboratory (NGL) and, in the first step, we compare them with displacements predicted by non-tidal atmospheric (NTAL), hydrospheric (HYDL), oceanic (NTOL), and barystatic sea level (SLEL) loading models provided by the GFZ Helmholtz Centre for Geosciences to obtain a consistent picture of GPS sensitivity to loadings over Europe. This part of the study allowed us to confirm a very high correlation but varied depending on the region of Europe. Then, we divided GPS stations regionally upon the results of noise analysis and the common mode error was determined using the probabilistic Principal Component Analysis (pPCA) method. We note a significant correlation between the NTAL model and the CME values, which indicates that in Europe, most of the CME is driven by the unmodeled atmospheric effect with some regional anomalies. Finally, we provide a discussion on the differences in the values of velocities of GPS permanent stations together with their uncertainties after removing the CME values.