The investigation of real-time LEO timing via GPS PPP with different RT products

Abstract

Low Earth Orbit (LEO) satellites mostly utilize crystal oscillators instead of high-performance atomic clocks mounted on medium to high-orbit satellites. Therefore, keeping high-precision time synchronization between LEO and GNSS satellites is the premise of realizing the high-precision application of LEO satellites. In this contribution, GPS precise point positioning (PPP) technology was employed to release precise timing for LEO satellites with different Real-time (RT) products. GRACE-FO C and GRACE-FO D satellites and five precise RT products from different analysis centers, which are CNES, GFZ, GMV, WHU, and CAS were chosen to achieve precise timing. The results indicated that the overall trend of clock difference fluctuations presented with all real-time products is generally consistent, fluctuating within the range of ± 4 ns. Furthermore, real-time precise products from GMV and GFZ exhibit significant fluctuations during the daily initial time period. Additionally, real-time products from WHU outperform other products and demonstrate greater stability. In terms of frequency stability, the clock stability of various analysis centers is generally consistent, with short-term stability (1280 s) reaching approximately 10−13 and long-term stability (10240 s) reaching around 10−14. WHU's timing stability is notably superior to other real-time products. In the time synchronization experiment, real-time products fluctuate within the range of ± 2 ns, while IGS final products fluctuate within ± 1 ns. In terms of time synchronization stability comparison, short-term stability (1280 s) still fluctuates around 10−13, and long-term stability (10240 s) fluctuates around 10−14. WHU exhibits relatively good overall stability, while GFZ shows comparatively lower overall stability.