Global Positioning System (GPS) station displacements in this work are derived using the so-called precise point positioning (PPP) technique with low-cost singlefrequency (SF) receivers. In the SF PPP, the ionosphere delay is the largest error source if the satellite orbits and clocks are well modeled. We use two strategies to minimize the ionosphere delay for an internal comparison: (1) correction using the global ionosphere map (GIM), and (2) estimates of the ionospheric total electron content (TEC) from SF observables (SFO). The trends of the station displacements derived from these two strategies consistently present a systematic movement toward the southwest. Here the trend is referred to the slope of a linear function used to fit the displacement data. Such a systematic movement is mainly caused by the semi-annual variation of the ionospheric TEC rather than the seasonal geophysical effect and the high-order ionosphere effect, both of which only cause the station displacements ranging from a few mm to a few cm. We present a statistical analysis in terms of correlation coefficients between the semi-annual TEC variation and the station displacement. The maximum correlation coefficient is higher than 0.8 in the U component, followed by the E and N components. In addition, the impact of the semi-annual TEC variation on the station displacement is approximately 0.71, 0.45, and 0.92 m in the north (N), east (E), and height (U) for a region close to the latitude 23°N and longitude 121°E. This suggests that the semi-annual TEC variation should be considered in a time series of station displacements derived by the SF-PPP.
The data used in this study are provided by the Central Geological Survey (CGS) of Taiwan. Anyone interested in the data, please contact the webpage (https://www.moeacgs.gov.tw/eng/MailBox/) directly.