Time transfer with nanosecond accuracy for the realization of International Atomic Time

Two-way satellite time and frequency transfer (TWSTFT) has become an important technical component in the process of the realization of International Atomic Time. To employ the full potential of the technique, especially for true time transfer, a dedicated calibration is necessary. This consists of the calibration either of the operational link at large, including every component involved, or of the involved ground stations' internal delays only. Both modes were successfully employed by circulating and operating a portable reference station between the sites involved. In this paper, we summarize the theoretical background for the different calibration modes applied and report examples of results from the 13 calibration campaigns performed up to now in Europe and between Europe and the United States. In all of these exercises, estimated uncertainties around 1?ns were achieved. Consecutive campaigns showed a very good reproducibility at the nanosecond level. Additionally, we address and briefly discuss sources that possibly limit the uncertainty for true time transfer employing TWSTFT.

[1]  D. Matsakis,et al.  On optimizing the configuration of time-transfer links used to generate TAI , 2006, Proceedings of the 20th European Frequency and Time Forum.

[2]  D. Piester,et al.  Description of the TWSTFT Station at METAS and Presentation of the Calibration Campaign 2006 , 2007, 2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum.

[3]  A. Bauch,et al.  Time comparisons between USNO and PTB: a model for the determination of the time offset between GPS time and the future Galileo system time , 2004, Proceedings of the 2004 IEEE International Frequency Control Symposium and Exposition, 2004..

[4]  Joseph Achkar,et al.  Design of a ku band delay difference calibration device for TWSTFT station , 2004, IEEE Transactions on Instrumentation and Measurement.

[5]  Z. Jiang,et al.  Comparison and combination of TAI time links with continuous GPS carrier phase results , 2006, Proceedings of the 20th European Frequency and Time Forum.

[6]  Judah Levine,et al.  Annual Precise Time and Time Interval ( PTTI ) Meeting 485 A LONG-TERM COMPARISON OF GPS CARRIER-PHASE FREQUENCY TRANSFER AND TWO-WAY SATELLITE TIME / FREQUENCY TRANSFER , 2007 .

[7]  Ph. Hartl,et al.  High accuracy global time transfer via geosynchronous telecommunication satellites with Mitrex , 1983 .

[8]  D. Kirchner,et al.  Two Way Satellite Time and Frequency Transfer (TWSTFT) : Principle, Implementation, and Current Performance , 1999 .

[9]  Jun Amagai,et al.  Delay Difference Calibration of TWSTFT Earth Station Using Multichannel Modem , 2007, IEEE Transactions on Instrumentation and Measurement.

[10]  Demetrios Matsakis,et al.  The Accuracy of Two-Way Satellite Time Transfer Calibrations , 2005 .

[11]  Gerard Petit,et al.  GPS All in View time transfer for TAI computation , 2008 .

[12]  D. Matsakis.  Time and frequency activities at the U.S. naval observatory , 2005, Proceedings of the 2005 IEEE International Frequency Control Symposium and Exposition, 2005..

[13]  T. E. Parker,et al.  Earth station errors in two-way time and frequency transfer , 1997 .

[14]  W. Lewandowski,et al.  Calibration of Three European TWSTFT Stations Using a Portable Station and Comparison of TWSTFT and GPS Common-View Measurement Results , 1998 .

[15]  Tadahiro Gotoh,et al.  Long-Baseline TWSTFT Between Asia and Europe , 2006 .

[16]  Demetrios Matsakis.  TIME AND FREQUENCY ACTIVITIES AT THE U , 2005 .

[17]  T.E. Parker,et al.  Sources of instabilities in two-way satellite time transfer , 2005, Proceedings of the 2005 IEEE International Frequency Control Symposium and Exposition, 2005..

[18]  A. Smith,et al.  Two-way satellite time transfer between USNO and PTB , 2005, Proceedings of the 2005 IEEE International Frequency Control Symposium and Exposition, 2005..

[19]  Edoardo V. Detoma,et al.  Sirio 1 timing experiment , 1978 .

[20]  I. Sesia,et al.  Calibration of six European TWSTFT earth stations using a portable station , 2006, Proceedings of the 20th European Frequency and Time Forum.

[21]  Michael Rost,et al.  PTB'S TIME AND FREQUENCY ACTIVITIES IN 2006: NEW DCF77 ELECTRONICS, NEW NTP SERVERS, AND CALIBRATION ACTIVITIES , 2006 .

[22]  F. Cordara,et al.  Calibration of the IEN-PTB TWSTFT link with a portable reference station , 2004 .

[23]  R. Dach,et al.  Comparison between frequency standards in Europe and the USA at the 10−15 uncertainty level , 2006 .

[24]  A. Bauch,et al.  Studies on Measurement Noise in the European TWSTFT Network , 2007, 2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum.

[25]  Gerrit de Jong,et al.  Automated delay measurement system for an Earth station for Two-Way Satellite Time and Frequency Transfer , 1994 .

[26]  T. Polewka,et al.  Time Transfer Between USNO and PTB: Operation and Calibration Results , 2004 .

[27]  J.H. Hahn,et al.  A Report on GPS and Galileo Time Offset Coordination Efforts , 2007, 2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum.

[28]  O. Koudelka,et al.  CALIBRATION OF FOUR EUROPEAN TWSTFT EARTH STATIONS WITH A PORTABLE STATION THROUGH INTELSAT 903 , 2005 .

[29]  D. Matsakis,et al.  GPS Carrier Phase Analysis Noise on the USNO-PTB Baselines , 2006, 2006 IEEE International Frequency Control Symposium and Exposition.

[30]  D. Kirchner,et al.  Two-way time transfer via communication satellites , 1991, Proc. IEEE.

[31]  E. F. Arias,et al.  Atomic time-keeping from 1955 to the present , 2005 .