Real-time Galileo/GPS PPP timing for LEO satellite via Galileo HAS

Abstract Ensuring high-precision time synchronization among low Earth orbit (LEO) satellites, as well as between LEO and global navigation satellite system (GNSS) satellites, is essential for enabling high-precision applications. As an integrated precise point positioning (PPP) augmentation service within the Galileo satellite navigation system, Galileo High Accuracy Service (HAS) offers free satellite ephemeris corrections for GPS and Galileo satellites to global users, effectively supporting real-time space-based autonomous GNSS PPP timing and time transfer for LEO satellites. To explore the performance of HAS in LEO satellite timing and time transfer, this study conducts an in-depth analysis of GRACE-FO and Sentinel-6A for experiments. The results indicated that during the study period, the short-term stability (1280 s) of GPS PPP timing for the GRACE-FO using HAS products was 3.64–5.55 × 10 −13 , whereas the long-term stability (10240 s) was 3.19–5.93 × 10 −14 . The short-term stability values of GPS, Galileo, and GPS-Galileo PPP timing for Sentinel-6 A using HAS products were 1.75–2.72 × 10 −12 , 6.97 × 10 −13 –1.04 × 10 −12 , and 6.79–8.46 × 10 −13 , respectively. The long-term stability values were 3.50–5.05 × 10 −13 , 3.75–5.04 × 10 −13 , and 3.44–4.65 × 10 −13 , respectively. Compared to reliable analysis centers, HAS showed comparable performance in Galileo and Galileo/GPS PPP timing; however, the short-term stability of GPS PPP timing was lower due to the inferior quality of its GPS products. Regarding the time transfer, HAS exhibited a short-term stability of 4.04–5.09 × 10 −13 (between GRACE-FO) and 1.94–2.30 × 10 −12 (between GRACE-FO C and Sentinel-6A), a long-term stability of 3.69–5.14 × 10 −14 (between GRACE-FO) and 3.81–5.29 × 10 −13 (between GRACE-FO C and Sentinel-6A) in GPS, which is inferior to currently reliable analysis centers. Compared to the International GNSS Service final product, HAS exhibited an average standard deviation of 0.49 ns and 2.59 ns for GPS PPP time transfer between GRACE-FO satellites and between GRACE-FO C and Sentinel-6A, respectively.