Filter-based Real-time GNSS Precise Orbit Determination Applied to Satellites in Maneuver

The accuracy and availability of real-time precise orbits are critical for real-time Global Navigation Satellite Systems (GNSS) users. Real-time orbits are estimated by either batch processing using least-squares adjustment at most International GNSS Service (IGS) Analysis Centers (ACs), or filter-processing, for example, at JPL and Wuhan University. The filter-processing has the advantage of high-update rates from 5 min to 5 sec (in the case of real-time clock), which is more suitable to handle satellite maneuvers. Currently, maneuver satellites are labelled as unhealthy in broadcast ephemeris, and not processed by the IGS ACs. However, for the robustness and availability of real-time GNSS users, it is important to provide reliable orbits and clocks for as many satellites as possible, especially for some special scenarios such as poor visibility of low-elevation satellites in canyon or urban areas. Moreover, if the satellite maneuver is not handled in time, it could severely deteriorate the orbit quality of all satellites. In this study, we implement the square root information filter (SRIF) for real-time GNSS orbit determination to achieve an update rate of 30 sec. We propose an automatic method to detect the satellite maneuver and adjust the stochastic constraints of orbital elements. The constraints applied to the epoch-wise orbital elements, which are essential for the SRIF-based POD, are checked based on its post-fit residuals and adjusted accordingly. Using the simulated real-time processing of GPS satellites during six months in 2022, we demonstrate that the satellite maneuver can be successfully detected instantaneously without degrading the accuracy of any satellites. Comparison with the 5 min sampling final orbit products from Center for Orbit Determination in Europe (CODE), there is no loss of accuracy in the along and cross components and the agreements is within 5 cm. In the radial component, the orbit difference is around 5 dm during the first one to two hours after the maneuvering, and the orbit accuracy converges to 5 to 10 cm after 4 hours. Due to the correlation between radial orbit and satellite clock, it is validated by the phase residuals of static precise point positioning (PPP) that such an accuracy causes no degradation to the positioning users. In addition, we evaluate the important contribution of rescued maneuver satellites using kinematic PPP under various simulated observing scenarios.