Multi-GNSS Ultra-Rapid Orbit and Clock Products from the USNO

Sharyl Byram and Christine Hackman

Abstract:	As an Analysis Center (AC) of the International GNSS Service (IGS), the United States Naval Observatory (USNO) produces GPS-based estimates of satellite orbits, satellite- and receiver-clock time corrections, and Earth-orientation parameters five times per day: once in a daily “rapid” process, and four times in an every-six-hours “ultra-rapid” process. As an additional service to the IGS, the USNO AC produces the IGS Final Troposphere estimates for an average of 325 stations daily. The USNO also estimates a GPS-carrier-phase based extrapolator of Very Long Baseline Interferometry (VLBI) based UT1-UTC estimates, known as “UTGPS,” 5 times/day. The USNO is expanding its GNSS product family by incorporating GLONASS observational data ultra-rapid processing. These ultra-rapid orbit and clock estimates are under consideration for inclusion in IGS GPS ultra-rapid combination (IGU) as well as the experimental GLONASS ultra-rapid combination (IGV) and will be the focus of this paper. As more and more IGS stations upgrade to multi-GNSS receivers, the result is improved global coverage from the GNSS constellations with increased observations per epoch. In particular, the stations at higher latitudes benefit from the global coverage of the higher inclination GLONASS satellite orbits. The incorporation of the GLONASS data affects stations used in the ultra-rapid network solution though selection of different baselines as a result of the increased observations at multi-GNSS receivers. The models and standards used in this multi-GNSS ultra-rapid processing are aligned to the IGS's Repro2 campaign [1] and is completed with the Bernese GNSS Software v5.2 [2]. To understand the impact of processing the GLONASS signals in addition to the GPS signals, the solutions from the multi-GNSS ultra-rapid processing are compared to the USNO's existing GPS-based ultra-rapid orbits and clocks estimates as well as to the GPS-based combination produced by the IGS. Comparison to the USNO operational product provides direct insight into the benefits and drawbacks of multi-GNSS based products with similar processing methods,. This also gives insight into what to expect as more GNSS systems are available for inclusion, such as GALILEO and BeiDou-2. The IGS's combination products gives an external source for comparison which allows for determining the quality of the multi-GNSS USNO solutions and the operational USNO GPS-based products in respect to slightly differing processing methods of other ACs. The purpose of this paper is to elaborate on the processing details and results of the incorporation of GLONASS observations using updated software and aligning to the IGS Repro2 models and standards. Additionally, it will provide analysis of the impact to estimated parameters from including non-GPS GNSS signals into the ultra-rapid processing. Future directions for the USNO's multi-GNSS products will also be discussed.
Published in:	Proceedings of the ION 2015 Pacific PNT Meeting April 20 - 23, 2015 Marriott Waikiki Beach Resort & Spa Honolulu, Hawaii
Pages:	151 - 156
Cite this article:	Byram, Sharyl, Hackman, Christine, "Multi-GNSS Ultra-Rapid Orbit and Clock Products from the USNO," Proceedings of the ION 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 2015, pp. 151-156.
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