The Effects of Seasonal Variation on GPS Height Component

In this study, the effects of seasonal variation on the vertical position accuracy of GPS calculated by time series analysis of continuous GPS stations were investigated. Weather changes, water vapor in the atmosphere affect the position accuracy of GPS and cause fluctuations in GPS height values. It is also known that the height component has more air passage changes. Since it is easier to interpret the effects of the height component due to its topographic features and seasonal changes are more effective than the rest of the country, four continuous GPS stations, covering the 2014-2019 date range, from the Turkish National Permanent GNSS Network (TUSAGA-Aktif) were used in the East of Turkey were chosen. The daily coordinates of the stations were obtained as a result of GAMIT/GLOBK software solution. By applying time series analysis to the daily coordinate values of the stations, statistically significant trend, periodic and stochastic components of the stations were determined. As a result of the analysis, the vertical annual velocities of the stations and the standard deviations of the velocities were determined.

For the stations determined according to the ellipsoid heights, the velocity and standard deviation values of the height component were calculated for each month, season and year. As the ellipsoid height increases, the velocity and its standard deviation values decrease. While the minimum velocity values are observed for the station with the lowest ellipsoidal height in winter, for the station with the highest ellipsoidal height in autumn, the minimum their standard deviation values are determined in winter for the station with the lowest ellipsoidal height, and in summer for the station with the highest ellipsoidal height. According to the results obtained, the coordinate displacements caused by seasonal variation may be important and their effects should be considered especially in high precision geodetic surveys.

In addition, the velocity values of the stations were calculated for different years, and a decrease was observed in the height component depending on the observation duration. As the observation duration for the height component increases, both the velocity values and their standard deviation values decrease. In order to avoid velocity estimation error completely, the data length should be more than 4.5 years.

Keywords: GPS height compenent, GPS time series, Seasonal effect, Velocity estimation