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Abstract:
Multi-GNSS solutions require handling differences in the system-specific biases. One option of the multi-GNSS Precise Point Positioning (PPP) solutions is to calculate a master clock parameter per epoch for GPS with inter-system biases for Galileo, GLONASS, and BeiDou. The other option is to calculate system-specific epoch-wise clock parameters for each GNSS system, however, this option increases the number of estimated parameters almost by a factor of four. In this study, we compare two different approaches to the clock parameter handling for GNSS stations connected to the different clocks: hydrogen masers, cesium, rubidium, and crystal oscillator clocks. We assess how different handling affects the estimated station coordinates in the long-term multi-GNSS PPP solutions for different clocks. Satellite clock products contain discontinuities at the day boundaries. Therefore, the calculated receiver clocks also contain jumps. We assess the impact of estimating inter-system biases as monthly and daily parameters with resetting at day boundaries, as well as resetting the clock parameters and the removal of all off-diagonal elements in the covariance matrix at the day boundaries. We evaluate the impact of neglecting the clock jumps and bias jumps on the estimated station coordinates. We compare the solution with resetting only the master clock parameter with the solution in which the clock parameters and biases are reinitialized at each day. Finally, we compare the results of multi-GNSS time transfer between the solutions using system-specific clock estimates and common clock parameters based on one master clock and inter-system biases.
