Piece-wise linear clock modeling for highly stable IGS H-maser stations in Precise Point Positioning

Global Navigation Satellite Systems (GNSS) are based on measuring signal propagation time, so that clock information is required for both the transmitting satellite and the receiving ground station. For Precise Point Positioning (PPP), synchronization errors of the receiver clock are usually estimated as epoch-wise biases with white noise as stochastic behavior. A major issue for the receiver clock estimates is the high correlation with the station height and the tropospheric zenith delay that results from the observation geometry. Introducing models to reduce the number of unknown clock parameters is one way to mitigate these correlations. However, adequate modeling requires a high degree of stability for the corresponding clock.

In this contribution, we show the results of modeling highly stable GNSS receiver clocks in PPP using piece-wise linear representations. We discuss different options to control the deterministic and stochastic part of the piece-wise linear model (interval length, parameter weighting, etc.). For 56 highly stable hydrogen maser (H-maser) stations of the International GNSS service (IGS), the impact of piece-wise linear clock modeling on correlated parameters, especially the sub-daily height estimates, is presented. The differences in the modeling impact of the individual receiver clocks are explained by categorizing the stations based on statistical and observational quality measures. In addition, the effects of individual processing options (used GNSS constellations, elevation cutoff angle) are shown.