Long-Term Analysis of Carrier Phase Residual Variations Using Geometry-Ionosphere-Free Combination of Triple-Frequency GPS Observations
Carrier phase measurements are critical for precision GNSS applications in navigation and geophysical remote-sensing. Multi-frequency GNSS measurements can be used to estimate frequency-dispersive effects on GNSS signals and to improve the precision of user range estimates. Previous work introduces optimal linear combinations of triple-frequency GNSS observables for producing ionosphere-free range estimates and geometry-free TEC estimates. In this work, we derive another linear combination of triple-frequency GNSS observables – the geometry-ionosphere-free combination (GIFC) – that highlights the presence of frequency-dependent systematic and stochastic errors that impact range and TEC estimates. We analyze the GIFC over a multi-year period for several GPS satellites transmitting triple-frequency signals, highlighting some of the prominent systematic errors impacting GNSS carrier phase measurements. We suggest that the main components of these errors are due to thermal oscillations in the satellite hardware, satellite antenna phase effects, and multipath oscillations. This work serves as a foundation for further improving the precision of range and TEC estimates using multi-frequency GNSS through addressing these systematic effects.