Impact of the GPS orbital dynamics on spurious interannual Earth deformation

Global Positioning System (GPS) daily position time-series have a standard precision of a few millimetres. However, GPS position series contain large temporal correlations that impede the observation of subtle interannual Earth deformation. We show that the specific configuration of the GPS constellation, compared to other Global Navigation Satellite Systems (GNSS), contributes to the temporal correlation. Based on the analysis of observed and simulated GPS, Galileo, GLONASS and BeiDou orbits, we determine that the GPS orbital dynamics are more prone to interannual drifts caused by their higher sensitivity to the lunisolar gravitational resonance. This leads to substantial changes in the observation geometry over time, which, combined with mismodelled station-dependent systematic errors, results in a larger temporal correlation for GPS position time-series. Improving the weighting of the GPS observations may mitigate the effect of geometry, which is absent in other GNSS constellations.