Bureau International des Poids et Mesures. Use for UTC. W. Lewandowski, Z. Jiang

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1 Bureau International des Poids et Mesures Fourteen Years of TWSTFT Use for UTC W. Lewandowski, Z. Jiang Time Department Bureau International des Poids et Measures 1/50

2 Outline Latest on UTC Latest on time transfer Principle of TWTT Early history Ongoing Now Oncoming coming years 2/50

3 Associate States and Economies of the CGPM Metre Convention 1875 General Conference on Weights and Measures (CGPM) meets every four years and consists of delegates from Member States. Diplomatic treaty Governments of Member States International Committee for Weights and Measures (CIPM) consists of eighteen individuals elected by the CGPM It is charged with supervision of the BIPM and affairs of the Metre Convention The CIPM meets annually at the BIPM International organizations Consultative Committees ( CCs ) Ten CCs normally chaired by a member of CIPM; to advise the CIPM; act on technical matters and take important role in CIPM MRA; comprise representatives of NMIs and other experts. CIPM MRA National metrology institutes ( NMIs ) International Bureau of Weights and Measures (BIPM) International centre for metrology Laboratories and offices at Sèvres 3/50

4 2009 Part. nations: M.States, Part. labs: 68-9 associates 4 4/50

5 Timescales at the BIPM 400 atomic clocks in 70 laboratories 13 primary frequency standards (8 labs) Measurement of Earth s rotation (IERS) All reported measurements of PFS Daily clock data, ~40 labs average steering leap seconds UTC(k) Circular T Monthly predictions of TT(BIPM) EAL TAI UTC Echelle Atomique Libre freq stability 0.4 x d Temps Atomique International freq accuracy ~ 3 x Temps Universel Coordonné, monthly TT(BIPMxy) Freq accuracy 2-3 x UTCr Rapid UTC, weekly annualy 5/50

6 Clocks participating to TAI/UTC (Number) 6/50

7 Drift of EAL, improving the long term stability EAL presented a drift of about /month with respect to TT(BIPM); Strong monthly frequency corrections (see Section 3 BIPM Circular T) have shown little of not effect; The algorithm (ALGOS) had a linear model for the clock frequency prediction Well adapted when it was developed, with young Cs clocks, no H- masers, few primary frequency standards 23% of the clocks in TAI are H-masers The Cs are aging g About a dozen PFS report measurements, most of them Cs fountains A new model has been implemented and incorporated in ALGOS, with a parabolic model for all clocks (Panfilo, Harmegnies, Tisserand). Circular T since August 2011 was calculated with the new model. 7/50

8 Results: y(eal)-y(tt) Starting from August 2011 the new algorithm is officially used in UTC calculation: 68.5 f(eal)-f(pfs) Normal lized Frequen ncy The frequency drift affecting EAL is completely removed MJD Period of application of the new algorithm 8/50

9 Rapid production of UTC (UTCr) Based d on daily data reported (daily) by contributing laboratories; Automatically generated weekly solution over four weeks of data (sliding solution); Weekly access to daily values of [UTCr- UTC(k)] ( Stability of UTCr comparable to UTC 9/50

10 Improving UTC for the 21 st century applications Better clocks (in labs) New PFS (in labs) Optical frequency standards d (in labs) Improved clock comparisons by refining time transfer (labs, BIPM) Improved algorithms (labs for UTC(k), BIPM for UTC) Providing UTC more frequently (BIPM Rapid UTCr) Impact on UTC(k) Impact on steering GNSS times to a representation of UTC Real-time developments 10/50

11 International time links Time section North America Europe Asia NRC APL ORB DLR IFAG CH LDS JV SP SMU OP NMC IEN UME KRIS SG NIMT NMLS BIRM NIM USNO PTB NPLI CRL NAO CNMP CNM NIST NPL TP OMH INPL NMIJ VSL CAO NTSC JATC TL ROA DTAG BEV AOS PL LT SU NIMB SCL ONBA TCC IGMA ONRJ CSIR AUS MSL South America Africa Oceania ORGANIZATION OF THE INTERNATIONAL TIME LINKS March 2004 Laboratory equipped with TWSTFT TWSTFT TWSTFT by Ku band with X band back-up Laboratory equipped with dual frequency reception GPS CV dual frequency link GPS CV dual frequency back-up link GPS CV single-channel link GPS CV single-channel back-up link GPS CV multi-channel link GPS CV multi-channel back-up link 11/50

12 ONBA IGMA NRC USNO CNMP BEV AOS CAO CSIR LT MIKE NIMB NIS NPLI ZMDM PL SP NIM HKO NAO NMLS NTSC JATC SG APL IT ORB IFAG SCL NICT BIRM TCC NPL PTB DLR AUS VSL CH TL ROA UME KRIS OP TP CNM NIST ONRJ DTAG INPL JV LDS NMC SMU OMH SU MSL NIMT NMIJ ORGANIZATION OF THE COMMON-VIEW INTERNATIONAL TIME August 2006 Laboratory equipped with TWSTFT (not yet used) TWSTFT by Ku band with X band back-up GPS multi-channel link TWSTFT link GPS multi-channel back-up link GPS single-channel link GPS dual frequency link GPS single-channel back-up link GPS dual frequency back-up link 12/50

13 MIKE LT NIMB CSIR NIS NRC CAO NPLI CNMP ONBA BEV ZMDM PL IGMA USNO AOS SP ORB NIM HKO NAO NMLS NTSC JATC SG APL IT IFAG SCL NICT BIRM TCC NPL PTB DLR AUS VSL CH TL ROA UME KRIS CNM NIST ONRJ OP DTAG INPL JV LDS NMC SMU OMH SU TP MSL NIMT NMIJ ORGANIZATION OF THE ALL-IN-VIEW INTERNATIONAL TIME LINKS September 2006 Laboratory equipped with TWSTFT (not yet used) TWSTFT by Ku band with X band back-up GPS multi-channel link TWSTFT link GPS multi-channel back-up link GPS single-channel l link GPS dual frequency link GPS single-channel back-up link GPS dual frequency back-up link 13/50

14 GPS all-in-view i and TWSTFT international ti time links 14/50

15 Time transfer GPS/GLONASS/TW data daily reported Only laboratories with non-adapted GPS receivers still send weekly files; All laboratories post data in specific ftp directories; Combined GPS/GLONASS and TWPPP links are routinely used in the calculation of UTC; New calibration system for GPS links, allowing maintenance of TW calibration; 15/50

16 Methods now in use ua/ns ub/ns GPS C/A-code SCH GPS C/A-code MCH GPS/GLONASS (comb.) GPS P TW/GPS P3 (combination) GPS PPP TWSTFT TW/GPS PPP (comb.) /50

17 TAI Links Year Labs Number GPS TWSTFT 17/ Number

18 Uncertainty of time transfer in UTC 7 u B /CA/GNSS 6 Uncertainty Type A Type B /ns 5 u B /C P/GNSS/TW 4 u A ns u B / TW 1 0 PPP+TW GPS SA ON Off MC/CV MC/AV P3/AV PPP/TW /50

19 Mod. σ y (τ) Loran- C GLONASS P-code code1ch GPS Carrier phase 1 hour 1 day 1 year 19/50

20 Principle of TWTT The symmetry in the two-way transfer when the signals go through either atmosphere or optical fibre Reciprocity D AB = D BA in Two-Way time transfer D AB D BA Lab A /T A Lab B /T B TWSTT: Earth station A Geo-satellite Earth station B through atmosphere TWOTT: Transceiver A Transceiver B through Optical Fibre link To balance the propagation path delays in the bi-directions 20/50

21 Early History /2 ECHO-I first Passive Communication Satellite NASA images TELSTAR st Active Communication Satellite RELAY 1965 Communication Satellite As a promising accurate time transfer technique, TWSTT started its experiments earlier than GNSS Echo-I: One-way time transfer, not ideal due to the unknown propagation delays; -1962, Telstar: The first transatlantic two-way clock comparisons between USNO-NPL (US-UK) Relay II: The first transpacific two-way clock comparisons between USNO-RRL (US-Japan). The type A (u A )andb(u B ) uncertainties were near 100 ns and 1000 ns respectively 1970s ATS-1, 1983 Intelsat-V: u A reached 200 ps level. 21/50

22 Early History /2 In 1987, NIST,USNO,NRC,TUG,NPL,NMi,VSL,DTAG,PTB,OCA... routine experiment 3P/week In 1992, several commercial satellite systems and modems available In March 1993, the BIPM ad-hoc Working Group transformed to CCTF WG on TWSTFT Then the TDEV of hundred ps was attainable. Conclusion: TWSTFT Earth-stations can be monitoredtobestabletoa: * TDEV of 100 ps for τ=24h-1200h (1d to 50d) * Freq. transfer at at τ =1 day 22/50

23 Summary Acknowledgements: We thank the pioneers of the TWSTFT: B Guinot, G de Jong, F Cordara, P Hetzel, D Kirchner, D Knight, A Soering, W Klepczynski, W Hanson and T J Quinn. We thank also all the TWSTFT laboratories for their contributions to UTC and to the reference [2] based on which this paper is written Jiang et al. Review and Preview TWTT, EFTF2013, July, Prague 23 23/50

24 Overlapping samples 24/50

25 GPS CV single channel TWSTFT Frequency stability of [UTC(NPL)( ) UTC(NIST)] by GPS CV single channel and by TWSTFT 25/50

26 Ongoing g 1999 present 1/6 ITU approved in 1995 the standard data format for TWSTFT; The first TWSTT link in UTC was TUG-PTB in Circular T139, Aug GPS therefore finished its solo role for UTC time link In 2000, there were four TW time links: TUG-PTB, VSL-PTB, NPL- PTB and USNO-NPL. The international UTC time link network in 2000 TW links in/between Asia, Europe and America in /50

27 Ongoing g1999 present 2/6 TW s contribution to UTC/TAI Lab GPS TW. AOS GPS TW AUS GPS TW CH GPS TW IT GPS TW KRIS GPS TW NICT GPS TW NIM GPS TW NIST GPS TW NMIJ GPS TW NPL GPS TW NTSC GPS TW OP GPS TW PTB GPS TW ROA GPS TW SG GPS TW SP GPS TW TL GPS TW USNO GPS TW VSL GPS TW 19 labs operate TW 28% over total 68 UTC labs 13 used for UTC NIM GPS TW They contribute tib t to UTC/TAI with clocks (71% of total) NTSC GPS TW /12 Primary Frequency Standards 91% SP GPS TW important t role 27/50

28 Ongoing 1999 present 3/6 Mobile TW calibrators The UTC links must be calibrated. Several calibration campaigns were organized in and between Europe, America and Asia. Calibration Period Laboratories/campaigns May-June 2003 IT-PTB-IT July 2004 PTB-OP-NPL-VSL-PTB Oct.-Nov PTB-SP-VSL-NPL-OP-IT-PTB May-June 2006 TUG-PTB-CH-TUG Sept.-Oct PTB-NPL-OP-IT-VSL-CH-TUG PTB,OP,SP,CH,AOS OPSPCH 28/50

29 Ongoing 1999 present 4/6 The Europe-Asia transcontinental link between NICT and PTB was established in Longest UTC TW baselines at NICT Establishment of the devices at NICT and PTB in 2005 at PTB 29/50

30 Ongoing g 1999 present 5/6 40 TW-o only / AOS-P PTB / ns TW+PPP / AOS-PTB / ns AOS-PTB points, σ=0.779 ns Diurnal and Data missing AOS-PTB points, σ=0.042 ns No longer diurnal and gaps σ x / ps TW TDev -9.6 AOS-PTB TW+PPP h/2 h d/8 d/4 d/2 day 3d week Averaging time Combination of TW and GPS 30/50

31 Ongoing 1999 present 6/6 SP CH Netwo ork TWST TT Euro ope NIST USNO As siaerica Am ROA IT VSL PTB OP 31/50

32 TW/GPS/GLN link comparisons 32/50

33 Link comparisons Check the quality of different techniques Scientific studies Information exchanges with the UTC labs i.g. the comparison of TW vs. GPS : 1. TW-GPS All in View ( ) 2. TW-GPS P3 (since 2004) 3. TW-GPS PPP (since 2007) 4. TW GLONASS (since 2009) TW-GPS&TW combination (since 2010) 33/50

34 Result of fthe time link Comparisons on ftp 34/50

35 Get in the directory: LkC Index of ftp://tai.bipm.org/timelink/lkc/ Up to higher level directory YYMM Name Size Last Modified /07/ :00: /07/ :00: /02/ :31: /03/ :57: /04/ :41: /05/ :49:00 LongTerm 10/04/ :44:00 BIPM_LKC_CFS-PTTI2005.doc ReadMe_LinkComparison_ftp_v7.doc 285 KB 07/10/ :00: KB 29/05/ :00:00 35/50

36 Get in the directory: YYMM Index of ftp://tai.bipm.org/timelink/lkc/0904/ Up to higher level directory Baseline Name AOSPTB CHPTB DLRPTB KRIS NICT KRIS PTB NICTPTB NTSCNICT USNO PTB Index of ftp://tai.bipm.org/timelink/lkc/0904/usnoptb/ Up to higher level directory Name Size Last Modified Dlk 15/05/ :49:00 Lnk 15/05/ :49:00 difference of links Links 36/50

37 ua(tl-nict) 0903 < 0.2 ns * -9.1 Time Dev., Scale D-10 seconds HM-HM: σ=0.148ns 0 8 s d/8 1.1 d/4 d/2 day ddd wk* Link(ns): Tw/Tai0903 TL-NICT/00-20#_, Total: 727/1 37/50

38 ua(nict-ptb) ns HM-CS: σ=0.220ns * Time Dev., Scale D-10 seconds d/8 d/4 d/2 day ddd wk * Link(ns): Tw/Tai0909 NICT-PTB/20-05#_, Total: 736/1 38/50

39 Oncoming In the coming gyears? 1/6 I. Use of TW DPN and Carrier phase TWSTFT code is affected by noise and diurnals. Further improvements should come from other observables, such as the DPN dual pseudo-random noise and Carrier Phase. TW DPN allows doubly reducing the measurement uncertainty, in particular that from the diurnals TW CP is hundred times more precise than code, TW CP transfer may reach a stabilities of 0.1 ns in time and in frequency. MDev of DPN, TW CP, TW code, GPS CP vs. a HM TW Code TW CP 39/50

40 Principle of TWTT The symmetry in the two-way transfer when the signals go through atmosphere or optical fibre Reciprocity D AB = D BA in Two-Way time transfer D AB D BA Lab A /T A Lab B /T B TWSTT: Ground station A Geo-satellite Ground station B through atmosphere TWOTT: Transceiver A Transceiver B through Optical Fibre To balance the propagation path delays in the bi-directions 40/50

41 Oncoming In the coming years? 2/6 II. Optical Fibre - TWOTT Long-term goal: Compare the optical clocks More than 14 UTC laboratories actively involved Already operational UTC(AOS)-UTC(PL) ( ) by AGH Immediate Applications in UTC: - Validate the BIPM GNSS calibrator with u B ~ 200 ps - Validate the new GNSS and TWSTFT techniques New challenges - the theoretical issues - the practical issues: data processing, format, programs 41/50

42 Oncoming In the coming years? 3/6 First Operational Optical Fibre Time Link 420 km between UTC Laboratories AOS-PL Combined uncertainty 112 ps 42/50

43 Oncoming In the coming years? 4/6 The AGH optical fibre transceivers at AOS UTC(AOS) UTC(PL) TDev One way Two way The real-time clock comparison between UTC(AOS) and UTC(PL) through a fibre link, 25 km fibre experiment at TL 43/50

44 Oncoming In the coming years? 5/6 Table 7.2 The first 25 lines of the proposed TW%TFT data file T%PTB in unit ns for delay and ps for statistical terms * tfptb * FORMAT 01 * LAB PTB * REV DATE * ES PTB01 LA: N LO: E HT: m * REF-FRAME FRAME ITRF * LINK 14 fibre: Dark Channel Length: Km Amplifiers: 6 * OPTICAL-TX: nm RX: nm * MODEM: Dedicated hardware SIGNAL: 1 PPS on square wave * Link Stabilization: YES * LINK 16 fibre: AAA Network Length: Km Amplifiers: 0 * OPTICAL-TX: nm RX: nm * MODEM: SATRE 037 SIGNAL: PRN, 20 Mcps * Link Stabilization: NO * CAL xxx TYPE: CAL xxx BRIDGED MJD: EST. UNCERT.: x.xxx ns * CAL 214 TYPE: CAL 141 BRIDGED MJD: EST. UNCERT.: ns * CAL 213 TYPE: CAL 142 BRIDGED MJD: EST. UNCERT.: ns * LOC-MON NO * COMMENTS unit in 0.1 ps * It is suggested adapting the ITU TWSTFT data format for TWOTFT. Hence all the data exchanges, processing, calibrations, computations and the related methodology can be kept with only slight modifications. i This will save huge time and man powers and speed up its applications. --- data body proposition (I) * EARTH-STAT LI MJD STTIME NTL TW DRMS SMP ATL REFDELAY RSIG CI S CALR ESDVAR ESIG TMP HUM PRES * LOC REM hhmmss s 0.1ps 0.1ps s 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps C % mbar PTB01 TIM X 1226X X 0020X X 2800X PTB01 PTB X 2491X X 0020X X 2800X PTB01 OCA X 1497X X 0020X X 2800X PTB01 IT X 1937X X 0020X X X 2800X PTB01 ROA X 2520X X 0020X X X 2800X /50

45 Oncoming In the coming years? 6/6 Application of TWOTT Time link calibrations within a few minute? Time transfers with 100 ps? Change in the UTC network configuration? A new era of the ground based techniques is back 45/50

46 RECOMMENDATION CCTF (2012): CCTF/12-35 v1 09 September 2012 Development of continental-scale fiber optical time and frequency transfer networks and support to studies of improved methods for intercontinental comparisons The Consultative Committee for Time and Frequency (CCTF), considering the continuing reduction in uncertainties and instabilities of frequency standards based on optical atomic transitions that the stabilities of the time and frequency transfer techniques currently used for long-distance comparisons around the world, GNSS and TWSTFT, are insufficient for the needs of comparisons between the new frequency standards, the demonstrated capability of fiber optical links to realise frequency comparisons over distances of up to the order of 1000 km, 46/50

47 CCTF recommends that CCTF/12-35 v1 09 September 2012 metrology institutes vigorously pursue the development of continental-scale fiber optical time and frequency transfer networks, research aimed at significantly improving time and frequency transfer over intercontinental distances be actively encouraged and supported, and national governments, metrology institutes, optical fiber network providers and operators, space agencies and other relevant bodies consult and coordinate with each other on access to the necessary infrastructures and on possible synergies with other applications of these infrastructures. 47/50

48 PIONIER INTERNATIONAL CONNECTIOS 48/50

49 Summary TW computation at the BIPM since 14 years Plays a major role in generation of UTC/TAI Combination of TW and GNSS added value More TW calibration are needed d TW DPN and CP expected TWOTT bringing major change Real-time developments Fundamental role of of CCTF WG on TWSTFT 49/50

50 Many thanks for your attention! 50/50