A TWSTFT Calibration Guideline and the use of a GPS Calibrator for UTC TWSTFT link Calibrations

Z. Jiang, D. Matsakis, V. Zhang, H. Esteban, D. Piestre, S.Y. Lin, E. Dierikx

Abstract:	Two-Way Satellite Time and Frequency Transfer (TWSTFT) links were first introduced to Coordinated Universal Time (UTC) generation in 1999. These TWSTFT links were calibrated by alignment with the corresponding GPS time links, of which the nominal uncertainty was 5 ns. In the past decade, the primary calibration technique for TWSTFT link calibrations was based on a TWSTFT mobile ground station (MS) with uncertainty at the level of 1 ns. The use of an MS for TWSTFT link calibration is limited by the availability of an MS, a common satellite transponder, transportation, and high cost. For example, due to the lack of a common transponder, a MS cannot be used for a stand-alone calibration of the NIST-PTB link (the link between the National Institue of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB)). Therefore, alternative techniques have been proposed and validated in recent years. Investigations for improving GPS time link calibrations have been performed since 2008. In 2011 this triggered the International Bureau of Weights and Measures (BIPM) to carry out a pilot study on using GPS link calibrations for the UTC TWSTFT time links. The study concluded that a link calibration uncertainty of 1.5 ns is attainable. Based thereon, the ‘TWSTFT Calibration Guidelines for the UTC Time Links’ recognize the GPS link calibration as an alternative technique for the calibration of TWSTFT links. In this paper, we first outline the new TWSTFT Calibration Guidelines for UTC Time Links (v3.0), which was approved at the 23rd meeting of the Consultative Committee for Time and Frequency (CCTF) Working Group on TWSTFT. It authorizes several techniques, including the GPS link calibration and the Triangle Closure Calibration (TCC). Then we discuss the attainable uncertainty of the GPS calibration. Finally we provide in the Annex an example report of using a GPS calibrator for a typical UTC time link calibration based on the US Naval Observatory (USNO) and PTB, UTC(USNO)-UTC(PTB) TWSTFT link calibration. Here we describe the characteristics of BIPM’s Measurement of Total Delay (METODE) Global Navigation Satellite System (GNSS) calibrator, its setup at a UTC laboratory, Lab(k), measurements, and its results. In this calibration, the GPS result differs from that of the TWSTFT MS by 0.9 ns with an uncertainty of 1.5 ns.
Published in:	Proceedings of the 47th Annual Precise Time and Time Interval Systems and Applications Meeting January 25 - 28, 2016 Hyatt Regency Monterey Monterey, California
Pages:	231 - 242
Cite this article:	Jiang, Z., Matsakis, D., Zhang, V., Esteban, H., Piestre, D., Lin, S.Y., Dierikx, E., "A TWSTFT Calibration Guideline and the use of a GPS Calibrator for UTC TWSTFT link Calibrations," Proceedings of the 47th Annual Precise Time and Time Interval Systems and Applications Meeting, Monterey, California, January 2016, pp. 231-242. https://doi.org/10.33012/2016.13169
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In