Refinement methods to improve integrated precise orbit determination of GNSS/LEO satellites based on regional ground stations

Abstract Precise orbit determination (POD) of Global Navigation Satellite System (GNSS) satellites is not always reliable due to factors such as limited ground tracking stations (GTS), which result in weak observation geometry and inaccurate estimates of GNSS orbits. Using LEO satellites as dynamic tracking stations to simultaneously determine the orbits of GNSS and LEO satellites in integrated POD (IPOD) has been shown to be very promising, but its performance with a regional GTS network is less impressive. In this study, we propose three refinement methods to improve the orbit accuracy of GNSS/LEO IPOD based on a regional GTS network. Each of the methods is intended to reduce the adverse effect of a particular factor. First, a two-step weighting method is proposed to address differences in the geometric strengths of geosynchronous, inclined geosynchronous and medium Earth orbit provided by their GNSS observations. Subsequently, the method of constraining the estimated orbits using a known position sequence is applied to stabilize the POD solution and improve the relatively low accuracy of GNSS satellites with poor tracking geometry, uneven trackability, and limited measurements from the regional GTS network. Additionally, considering differences in GNSS observation quality from LEO satellites, the Helmert variance estimation method is used to assign proper weights to the observation data. Finally, the sequential implementation of these three methods constitutes a comprehensive IPOD refinement scheme. Various regional IPOD experiments are performed using spaceborne GPS/BDS-2 data from 14 LEO satellites to validate the effectiveness of these methods. The results show that the progressive, cumulative use of these three methods can gradually improve the orbital accuracy of regional IPOD, and the overall comprehensive refinement scheme can improve the orbit accuracy by varying degrees of 4–50% for different types of satellites. Particularly, a remarkable accuracy improvement of 28% is achieved for GPS satellites, and an average orbit accuracy of 3–9 cm is realized for all GPS/LEO satellites using only five regional GTSs in GPS/LEO IPOD experiments. These results demonstrate that the refinement methods proposed in this paper are essential for achieving high-precision IPOD based on a regional GTS network.