SRIF-based integrated precise orbit determination for GPS and LEO constellations: impact analysis of ground-station and LEO configurations

High-precision real-time satellite orbit products are prerequisite for achieving high-performance navigation and positioning services. This study develops an integrated precise orbit determination approach that combines GPS and low Earth orbit (LEO) satellites using the square root information filtering algorithm to improve the convergence time and accuracy of GPS real-time satellite orbits. By collecting data from varying numbers of global ground stations and LEO satellites (Sentinel-3A/B, GRACE-C/D, Swarm-A/B/C), GPS and LEO satellite orbits were determined synchronously. Orbit convergence time and accuracy were evaluated against the official reference products. Results show that, with 9 ground stations, adding 7 LEO satellites decreases the GPS orbit convergence time in the along-track, cross-track, and radial directions from 28.0, 28.3, and 21.8 h to 1.9, 3.9, and 14.3 h, respectively, achieving remarkable improvements of 93%, 86%, and 34%. Increasing the number of ground stations to 79 further reduces the convergence time to 0.7, 1.4, and 10.9 h in the three directions. For LEO satellites, increasing ground stations from 9 to 79 decreases the average convergence time across all three directions by 44%–70%. In terms of GPS orbit accuracy after convergence, the configuration of 7 LEO satellites with 9 ground stations reaches accuracies of 6.5, 3.8, and 3.0 cm in the along-track, cross-track, and radial directions, which is improved by 64%, 66%, and 48%, respectively, compared to the results without LEO satellites. When 79 ground stations are used, the GPS orbit accuracy is further improved to 5.0, 2.5, and 2.6 cm in the three directions. Notably, the three-dimensional GPS orbit accuracy reaches 6.8 cm with 19 ground stations and 7 LEO satellites, which outperforms the accuracy level of 7.4 cm obtained utilizing only 79 ground stations. These results indicate that the optimal deployment of LEO satellites can effectively compensate for ground network limitations while maintaining high-precision real-time orbit determination.