Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

The 2015 TWSTFT calibration for UTC and related time links



Zhiheng Jiang, Dirk Piester, Christian Schlunegger, Erik Dierks, Javier Galindo, Demetrios Matsakis, Victor S. Zhang


Two-Way Satellite Time and Frequency Transfer (TWSTFT or TW) is one of the primary time transfer techniques for UTC generation. Although it has expensive financial requirements it provides highly accurate calibration, and provides both robustness and complementarity to GNSS observations. For the generation of UTC, only the links involving the pivot laboratory (the PTB at present) need to be calibrated. They are a small part of the total number of links observed by the TW network. Some laboratories make use of TW time comparisons for applications other than UTC computation, and in such cases Triangle Closure Calibration (TCC) gives the opportunity to calibrate these links without direct, dedicated calibration measurements. The principle of TCC is based upon requiring the closure sum of the three co-joined links to be zero. If two of them are calibrated, we apply the necessary calibration correction to the third link to zero the closure sum. The systematic uncertainty (uB) of the third link is the RSS (square root of the summed squares) of the systematic uncertainties of the calibrated links' values and the closure sum standard deviations. In this paper, a review of the TCC method is presented, followed by the results of the BIPM 2015 calibration computation. Finally, we discuss the comparison between the TW and the GPS time link, which have been calibrated independently in recent years.
Proceedings Title
The European Frequency and Time Forum (EFTF)
Conference Dates
April 4-7, 2016
Conference Location
York, UK
Conference Title
30th European Frequency and Time Forum


Calibration, CALR, ESDVAR, TCC, TWSTFT or TW, TW Network, Uncertainty


Jiang, Z. , Piester, D. , Schlunegger, C. , Dierks, E. , Galindo, J. , Matsakis, D. and Zhang, V. (2016), The 2015 TWSTFT calibration for UTC and related time links, The European Frequency and Time Forum (EFTF), York, UK (Accessed June 20, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created April 3, 2016, Updated October 12, 2021