# Accuracy Analysis of GNSS Hourly Ultra-Rapid Orbit and Clock Products from SHAO AC of iGMAS
## 4 Summary and Conclusions  
Due to the demand of hourly ultra-rapid GNSS products with less latency, high accuracy, and updated rates for real-time or near-real-time studies and applications, we mainly discussed a new strategy and method for generating 6-hourly and 1-hourly GNSS orbit and clock products. The new method, which combined serial and parallel threads (CSPT), is studied in this contribution, and is different from previous researches. A new method of orbit prediction is also introduced and shows better accuracy compared to the old method. The computational efficiency, accuracy, and precision of the new strategy and method are discussed and analyzed in detail.  
The 6H and 1H GNSS orbit products were compared with reference products, with high accuracy from IGS/MGEX. Generally, the RMS of the observation session for the 6H orbit is comparative to 1H. However, the accuracy of 6H decreases when the prediction session increases. GPS shows the best accuracy, followed by GLONASS, Galileo, and BDS-MEO/IGSO/GEO. Moreover, the accuracy of 1H orbit is improved about 1%, 31%, 13%, 11%, 23%, 9% for the observation sessionand18%, 43%, 45%, 34%, 53%, 15% for the  
Figure 9: Average RMS of 6-hourly (**a**) and 1-hourly (**b**) GNSS clock versus reference products from IGS/MGEX.  
prediction session of GPS, GLONASS, Galileo, BDS MEO, IGSO, and GEO, relative to 6H orbit.  
The accuracy of 6H and 1H clock, with respect to reference clock products, are also analyzed. The mean SD of the observation session for the 6H clock is no more than 0.16 ns, and the GPS shows the best accuracy, followed by BDS, GLONASS, and Galileo. The mean SD of the GNSS prediction clock is less than 0.18 ns, which is a little worse than the SD of the observation session. The mean SD for the 1H clock is less than 0.16 ns for the observation session or even the 1 st-2 nd hour prediction session, which benefits from the higher updated rate and shorter prediction session.  
The 1H orbit and clock productions show better accuracy and precision relative to 6H. Some problems appearing in stations or satellites can be found and solved earlier and by the 1H procedure, which is useful for user applications.  
The results show the feasibility of the optimized CSPT method for GNSS hourly ultra-rapid orbit and clock products. The accuracy of the 6H and 1H orbit and clock verify the availability and reliability of the hourly ultra-rapid products, which can be used for real-time or near-real-time applications. Moreover, the CSPT method caneasily avoid the problems caused by a bad satellite or station, and it improves the computational efficiency, continuity, and stability of ultra-rapid productions. Thus, the CSPT method shows encouraging prospects for better performance and deserves wide application.  
Conceptualization, Q.C. and S.S.; methodology, Q.C.; software, Q.C.; validation, W.Z. and Q.C.; formal analysis, S.S.; investigation, Q.C. and W.Z.; resources, S.S. and Q.C.; data curation, Q.C.; writing--original draft preparation, Q.C.; writing--review and editing, S.S. and W.Z.; visualization, Q.C.; supervision, S.S.; project administration, S.S.; funding acquisition, Q.C. and S.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by ZFS (Y9E0151M26) and National Natural Science Foundation of China (No. 12073063, 11403083).  
Not applicable.  
Thanks to IGS/MGEX, iGMAS, and CMONOC for providing the data and products to support this study. The reviewers and editors of this paper are also appreciated by the authors.  
The authors declare no conflict of interest.