Precise orbit determination for LEO satellites: single-receiver ambiguity resolution using GREAT products

ABSTRACT

In recent years, the large Low Earth Orbit (LEO) constellations have become a hot topic due to their great potential to improve the Global Navigation Satellite Systems (GNSS) positioning performance. One of the important focus is how to obtain the accurate and reliable orbits for these constellations with dozens of LEO satellites. The GNSS-based Precise Orbit Determination (POD) will be exclusively performed to achieve this goal, where the Integer Ambiguity Resolution (IAR) plays a key role in acquiring high-quality orbits. In this study, we present a comprehensive analysis of the benefit of the single-receiver IAR in LEO POD and discuss its implication for the future LEO constellations. We perform ambiguity-fixed LEO POD for four typical missions, including Gravity Recovery and Climate Experiment (GRACE) Follow-On (GRACE-FO), Swarm, Jason-3 and Sentinel-3, using the Uncalibrated Phase Delay (UPD) products generated by our GREAT (GNSS+ REsearch, Application and Teaching) software. The results show that the ambiguity fixing processing can significantly improve the accuracy of LEO orbits. There are negligible differences between our UPD-based ambiguity-fixed orbits and those based on the Observable Signal Bias (OSB) and Integer Recovery Clock (IRC) products, indicating the good-quality of UPD products we generated. Compared to the float solution, the fixed solution presents a better consistency with the external precise science orbits and the largest accuracy improvement of 5 mm is achieved for GRACE-FO satellites. Meanwhile, the benefit can be observed in laser ranging residuals as well, with a Standard Deviation (STD) reduction of 3–4 mm on average for the fixed solutions. Apart from the absolute orbits, the relative accuracy of the space baseline is also improved by 20–30% in the fixed solutions. The result demonstrates the superior performance of the ambiguity-fixed LEO POD, which appears as a particularly promising technique for POD of future LEO constellations.

KEYWORDS:

• Precise orbit determination
• single-receiver ambiguity resolution
• onboard GPS observation
• LEO

Acknowledgments

The numerical calculations in this study have been done on the supercomputing system in the Supercomputing Center of Wuhan University.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

We are grateful to International GNSS Service (IGS) for providing the precise orbit and clock products of GPS as well as OSB and IRC correction products at ftp://cddis.gsfc.nasa.gov for free. The UPD products generated by GREAT software can be accessed at http://igmas.users.sgg.whu.edu.cn/. The data onboard GRACE-FO, Swarm, Jason-3 and Sentinel-3 are publicly available from ftp://isdcftp.gfz-potsdam.de, ftp://swarm-diss.eo.esa.int, ftp://ftp-access.aviso.altimetry.fr and https://scihub.copernicus.eu respectively.

Additional information

Funding

This work was supported by National Natural Science Foundation of China [41974027] and Sino-German mobility programme [M-0054].

Notes on contributors

Xingxing Li

Xingxing Li is currently a professor at Wuhan University. He has completed his BSc degree at the School of Geodesy and Geomatics at Wuhan University. He obtained his PhD degree at the Department of Geodesy and Remote Sensing of the German Research Centre for Geosciences (GFZ). His current research mainly involves GNSS precise position and orbit determination, and multi-sensor integrated navigation.

Yujie Qin

Yujie Qin is currently a postgraduate student at Wuhan University. She received her BSc at the School of Geodesy and Geomatics at Wuhan University in 2019. Her research currently focuses on the precise orbit determination for the LEO satellites and the determination for the Earth orientation parameters.

Keke Zhang

Keke Zhang is currently a PhD candidate at Wuhan University. He has completed his BSc at the School of Geodesy and Geomatics in Wuhan University in 2016. His area of research currently focuses on the precise orbit determination for LEO satellites and the integrated processing of LEO and GNSS.

Jiaqi Wu

Jiaqi Wu is currently a PhD candidate at Wuhan University. He has completed his BSc at the School of Geodesy and Geomatics in Wuhan University in 2017. His area of research currently focuses on precise orbit determination for LEO and GNSS satellites and undifference ambiguity resolution.

Wei Zhang

Wei Zhang is currently a PhD candidate at Wuhan University. He has completed his BSc at the School of Geodesy and Geomatics in Wuhan University in 2018. His area of research currently focuses on integrated orbit determination of LEO and GNSS satellites.

Qian Zhang

Qian Zhang received her BSc at the School of Geodesy and Geomatics at Wuhan University in 2018 and obtained her Master’s degree at the School of Geodesy and Geomatics at Wuhan University in 2021. Her research focused on the determination for the Earth orientation parameters.

Hongmin Zhang

Hongmin Zhang is currently a postgraduate student at Wuhan University. She received her BSc at the School of Geodesy and Geomatics at Wuhan University in 2019. Her research currently focuses on the realization of reference frame based on GNSS and SLR.