Improved prediction of GPS satellite clock sub-daily variations based on daily repeat
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High-precision estimates of GPS satellite clock errors reveal systematic sub-daily clock bias variations on the order of 1 ns. The low noise levels in the Rubidium Atomic Frequency Standards onboard GPS IIR, IIR-M, and IIF satellites provide visibility of these small, but systematic behaviors. Prior studies have reported on this phenomenon and sought to characterize the specific frequency components present and to identify potential causes of the observed periodic variations. Our research focuses on the repeatability of the clock variations and the potential for using observed variations directly to predict future clock behavior. Results are presented and compared to IGS Ultra-rapid and broadcast message predictions for all operating GPS satellite clocks for a 1-month period in July 2017. During this time, the accuracy of the proposed sub-daily variation prediction is better than 0.15 ns (RMS) for 8 out of 9 GPS Block IIF Rb clocks and under 0.3 ns (RMS) for most GPS IIR and IIR-M Rb clocks. This approach is complementary to existing techniques for estimating longer-term clock rates and drift and can be combined with them to improve the fidelity of predictive satellite clock models for real-time GPS position, navigation, and timing applications.
KeywordsGPS satellite clocks Rubidium clock Allan variance Repeatability
The authors would like to thank the anonymous reviewers for their valuable comments and recommendations and Dr. Ben Bradley and Dr. John Pratt for their MATLAB codes used in support of this work.
Funding for a portion of this work was provided by Braxton Technologies LLC (Subcontract No. 1059‐2015‐1).
- Axelrad P, Larson KM, Jones B (2005) Use of the correct satellite repeat period to characterize and reduce site specific multipath errors. In: Proceedings of ION GNSS-2005, Long Beach, CA, pp 2638–2648Google Scholar
- Beard R, White J, Brad J, Myers T, Reid W, Danzy F, Buisson J (2000) Long term ground test results for two GPS Block IIR rubidium clocks. In: Proceedings of ION NTM 2000, Anaheim, CA, pp 381–387Google Scholar
- Dupuis RT, Lynch TJ, Vaccaro JR, Watts ET (2010) Rubidium frequency standard for the GPS IIF program and modifications for the RAFSMOD program. In: Proceedings of ION GNSS + 2010, Portland, OR, pp 781–788Google Scholar
- Epstein M, Dass T (2001) Management of phase and frequency for GPS IIR satellites. In: Proceedings of the 33th annual precise time and time interval systems and applications meeting, Long Beach, California, pp 481–492Google Scholar
- GPS (2008) Global positioning system standard positioning service performance standard, 4th edn, September 2008Google Scholar
- IGS (2014) Real-time service fact sheet. http://rts.igs.org/monitor/
- Riley WR (2008) Handbook of frequency stability analysis. NIST special publication 1065 National Institute of Standards and Technology, Boulder, COGoogle Scholar
- van Diggelen F (2009) A-GPS, assisted GPS, GNSS, and SBAS. Artech House, Boston, MAGoogle Scholar
- Vannicola F, Beard R, White J, Senior K, Kubik K, Wilson D (2010) GPS block IIF rubidium frequency standard life test. In: Proceedings of the 23rd international technical meeting of the satellite division of the ION GNSS + 2010, Portland, OR, pp 812–819Google Scholar