Multi-GNSS clock combination with satellite attitude correction

International GNSS Service (IGS) has been continuously providing high-precision combined GPS orbit and clock products, which is widely used in various scientific research and operational applications. However, with the prosperity of Global Navigation Satellite System (GNSS), combination strategies of multi-GNSS (GPS, GLONASS, Galileo and BDS) products is now urgently needed. Besides, due to the coupling relationship between satellite attitudes and clocks, the clock consistency during combination can be further improved by considering attitude differences. Therefore, we proposed a multi-GNSS clock combination strategy considering attitude correction. It is found that GPS clock combination residuals can be reduced by 80% at most after applying attitude correction. Additionally, we conducted static and kinematic positioning for 142 globally distributed stations using the combined products. Compared to the products provided by a single analysis center, the GPS/GLONASS/Galileo combined products are more stable and can improve the positioning quality up to 22.7%, 16.7% and 18.3% for the three components during kinematic positioning. Adding attitude corrections during clock combination can improve the kinematic positioning accuracy up to 65.3% at a single station.