Local realization of UTC

1. Local realization of UTC Is it that simple?

2. Use of local UTC • Coordination at a local level with UTC • Certification for legal or scientific purposes • Does not absolutely need accuracy at the physical realization level. Stability is more important. • Needs good link with BIPM, direct or through another laboratory, and good traceability.

3. What is needed? • An atomic clock • If high accuracy (uy<10-12) better than 31ms/year • A link with other labs and BIPM • GPS is the shorter and easier route; BIPM routine or SIM GPS • Then intrinsic accuracy is not even needed, can be taken account for since we have a live KCRV, running continuously. • Some dedication • Needs continuous checking. • Time scale algorithm if more than one clock

4. Local UTC • Have to take account of altitude • When calibrating a client’s clock • Running faster at higher altitude • 10-16/m or 10-13/km • Warn the client, correct for them if necessary

5. Warnings • Local time scale needs to be independent, even if you align frequency on BIPM from time to time. • If you contribute to BIPM, tell them when you apply a change to your clock(s). • It allows you to track UTC and still contribute useful data. • If you do not warn BIPM, BIPM time algorithm will be fooled. • This is your KCRV: don’t mess it up!

6. BIPM Circular T Published monthly on BIPM web page, it is the KCRV that validates all your measurements! CIRCULAR T 213 ISSN 1143-1393 2005 OCTOBER 12, 16h UTC BUREAU INTERNATIONAL DES POIDS ET MESURES ORGANISATION INTERGOUVERNEMENTALE DE LA CONVENTION DU METRE PAVILLON DE BRETEUIL F-92312 SEVRES CEDEX TEL. +33 1 45 07 70 70 FAX. +33 1 45 34 20 21 tai@bipm.org 1 - Coordinated Universal Time UTC and its local realizations UTC(k). Computed values of [UTC-UTC(k)] and uncertainties valid for the period of this Circular. From 1999 January 1, 0h UTC, TAI-UTC = 32 s. From 2006 January 1, 0h UTC, TAI-UTC = 33 s. Date 2005 0h UTC AUG 27 SEP 1 SEP 6 SEP 11 SEP 16 SEP 21 SEP 26 Uncertainty/ns Notes MJD 53609 53614 53619 53624 53629 53634 53639 uA uB u Laboratory k [UTC-UTC(k)]/ns AOS (Borowiec) -0.8 2.9 11.5 -7.3 -16.2 -8.3 -6.1 1.6 5.2 5.4 APL (Laurel) -17.6 -14.8 -7.3 -2.9 -6.2 -8.4 -12.3 1.6 5.2 5.5 AUS (Sydney) -655.1 -641.2 -648.8 -638.0 -637.0 -645.0 -651.1 3.2 6.4 7.2 BEV (Wien) -86.1 -90.8 4.6 2.3 -3.0 -5.5 -0.4 1.6 5.2 5.4 (1) BIRM (Beijing) - -736.5 -759.4 -776.8 -793.5 -811.7 -826.6 5.1 20.4 21.0 CAO (Cagliari) -2383.2 -2360.2 -2339.0 -2324.0 -2307.7 -2320.4 -2288.1 1.6 7.2 7.3 CH (Bern) -13.9 -17.7 -25.6 -25.4 -21.6 -12.2 -4.2 0.8 5.2 5.2 CNM (Queretaro) 60.9 53.8 54.6 47.7 47.7 46.1 48.4 5.0 20.3 20.9 CNMP (Panama) -3430.6 -3471.3 -3514.1 -3552.7 -3580.7 -3613.1 -3640.6 4.0 7.2 8.2 CSIR (Pretoria) 4452.4 4358.8 4268.3 4185.3 4104.2 4035.7 3953.1 3.0 20.1 20.3

7. Circular T • It is a source of information for each participating laboratory: UTC-UTC(k) • It is provides the uncertainties associated with each link to the laboratories • It also provides the daily average value of UTC vs GPS time; useful to check the agreement of GPS time with UTC.

8. Why Circular T is one month late? • Instantaneous results are not possible • ALGOS, the time scale algorithm used by BIPM is based on a 60 days evaluation of 5 days measurements. • TAI, UTC are computed once a month, based on 5 days measurements to smooth out the short term noise associated with the links. • It also allows participating laboratories to correct for erroneous or missing data before calculation of TAI/UTC.

9. How to use Circular T • Use to track one laboratory behavior respect to the other laboratories participating • Can be used to correct local time scale before it is too far from UTC • Beware of warning BIPM of any change in your laboratory: delay (new cable, etc) offset in frequency, new clock, etc • Provides the basis for your frequency and time calibration uncertainties.

10. Circular T as a KCRV Cirular T is the Key Comparison Reference Value CCTF-K2001-UTC • Calculation of the reference time scale UTC (Coordinated Universal Time)1977 – • Note the date above: it has been continously running for the last 28 years! • Some other CCs have one KCRV over same period.

11. How are we doing? • We will look at some laboratory within SIM using the Circular T data • UTC(NRC) Ottawa • UTC(NIST) Boulder • UTC(CNM) Queretaro • UTC(ONRJ) Rio de Janeiro • UTC(ONBA) Buenos Aires • UTC(IGMA) Buenos Aires • UTC(CNMP) Panama

12. 9 years of IGMA, NRC, NIST

13. Two years of some UTC-UTC(k)

14. Note about UTC-UTC(k) • All laboratories seem to have a more stable UTC(k) in the last seven months

15. Slopes and offset removed

16. Except ONBA, every lab is within a time window of less than ±50 ns

17. Total ADev ONBA NRC CNMP IGMA CNM ONRJ NIST UTC

18. TDev for some UTC(k) ONBA CNMP IGMA ONRJ NRC CNM NIST UTC

19. 5-day noise and links uncertainty Link Type uA/ns uB/ns TDev(UTC(k)) CNM /NIST GPS SC 5.0 20.0 3.0 CNMP/USNO GPS MC 4.0 7.0 5.0 IGMA/USNO GPS MC 5.0 20.0 5.0 NIST/PTB TWSTFT 0.5 5.0 0.5 NPL /PTB GPS MC 1.5 4.0 NRC /USNO GPS SC 3.0 15.0 3.0 ONBA/USNO GPS MC 5.0 7.0 32.0 ONRJ/NIST GPS SC 5.0 20.0 5.0 USNO/PTB TWSTFT 0.5 1.1 Except ONBA, all the labs are at the limit of the GPS link noise uncertainty uA. Note that the type B uncertainty (estimated uncertainty of calibration) does not affect the uncertainty of frequency transfer but should be added to the TDev in the case of time transfer.

20. conclusion • All the laboratories contributing to BIPM in SIM are doing a good job of maintaining local UTC • Join the SIM common-view GPS comparison network