Two-Way Time Transfer via Satellites and Optical Fibers. Physikalisch-Technische Bundesanstalt

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1 Two-Way Time Transfer via Satellites and Optical Fibers Dirk Piester Physikalisch-Technische Bundesanstalt Time Dissemination Group (4.42) 42) 1

2 Outline Two-way satellite time and frequency transfer (TWSTFT) How does it work? Clock comparisons Latest developments New Experiments Calibration Time transfer through optical fibers (TTTOF) Local comparisons Remote comparisons Summary 2

3 Two-way satellite time and frequency transfer (TWSTFT) How does it work? Phase coherent to a local clock pseudo random noise phase-shift keying spread spectrum signals are exchanged between two stations typically in the Ku- band GHz Modulation of operational links is typically Mcps, corresponding to occupied transponder bandwidth of about 2 4 MHz. 3

4 Two-way satellite time and frequency transfer (TWSTFT) How does it work? Applied chiprate (bandwidth) together with signal to noise ratio translates directly into jitter of clock comparison using a 1 pulse per second (1pps) as the reference. 4

5 Two-way satellite time and frequency transfer (TWSTFT) How does it work? Time transfer with an uncertainty at the level of 1 ns Frequency comparsions at the level 5

6 Two-way satellite time and frequency transfer (TWSTFT) The global metrology network ASIA/USA EUR/USA ASIA/EUR ASIA AMC-2 T-11N AM-2 GE-23 America: NIST, USNO Europe: AOS, CH (METAS), IPQ, IT (INRIM), NPL, OCA, OP, PTB, PTF1 (ESA), PTF2 (ESA), ROA, SP, SU (VNIIFTRI), TIM (TimeTech), TUG, VSL Asia: NICT, NIM, NMIJ, NPLI, NTSC, TL Not all stations ti can access to all intercontinental ti t links. 6

7 Two-way satellite time and frequency transfer (TWSTFT) The global metrology network Two examples: 1) UTC(PTB) UTC(OP) 7

8 Two-way satellite time and frequency transfer (TWSTFT) The global metrology network Two examples: 2) UTC(PTB) UTC(USNO) 8

9 Two-way satellite time and frequency transfer (TWSTFT) Clock comparisons Primary Cs fountain clock comparisons are being made since 2001 using TWSTFT. [T. Parker et al First comparison of remote cesium fountains Proc. IFCS 2001] Comparison between European fountains in 2004 [A. Bauch et al., Metrologia, 2006] Fountain comparison result Comparison of hydrogen masers at NPL and OP 9

10 Two-way satellite time and frequency transfer (TWSTFT) Clock comparisons Primary fountain clocks PTB CSF1 and NICT CsF1 were compared via GPS, TWSTFT and BIPM computation of TAI. [M. Fujieda et al., Proc. EFTF 2008, Toulouse, France] 10

11 Two-way satellite time and frequency transfer (TWSTFT) Clock comparisons May 2013: Comparison of fountain clocks in Europe and Asia using TWSTFT and GPS PPP Coordination / data computation: Miho Fujieda (NICT) / Aimin Zhang, Kun Liang (NIM) Laboratory Country Fountains Identification involved NIM PR China Csf NPLI India CsF1 PTB Germany CSF1, CSF2 SU Russia Cf1Cf2 Csf1, Csf2 Uncertainty of frequency comparisons slightly above 1e 15. Cs fountains agree within estimated uncertanties. Results will be reported soon. June 2013: Comparison of Sr optical lattice clocks at NICT and PTB using TWSTFT carrier phase Results under evaluation 11

12 Latest developments Dual pseudo-random noise TWSTFT NICT has developed TWSTFT using dual pseudo-random noises (DPN), where two coded signals with a lower chip rate are used with separatelyallocated frequencies. In this scheme, spreading the signals with a gap frequency is equivalent to using a wider chip rate signal. A measurement precision of 16 ps was achieved using 128-kbps coded signals with a frequency separation of 20 MHz. NICT and TL have occasionally performed DPN TWSTFT on the link by GE-23 North East Asia beam and the achieved time transfer stability is shown in the following figure. [T. Gotoh et al., IEEE IM, 2011] [W. H. Tseng et al., IEEE TUFFC, 2012] 12

13 Latest developments Dual pseudo-random noise TWSTFT For further improvement of the measurement precision, NICT has started the development of carrier- phase-based TWSTFT. In a short baseline with a length of 150 km, the measurement precision of 0.4 ps was achieved and the time variation showed good agreement with the results of GPS carrier phase. [M. Fujieda et al., EFTF 2012] Also at OP the implementation of the carrier phase technique led to a significant improvement of the measurement noise: frequency stability of 1x10-12 at 1 s and 3x10-14 at 100 s were obtained with OP01 and OP02 in collocation. However, a degradation of the stability is observed at 300 s. [A. Kanj et al., EFTF 2012] 13

14 Two-way satellite time and frequency transfer (TWSTFT) TWSTFT carrier phase between NICT (Japan) and PTB (Germany) Intercontinental clock comparison using the phase information of the Ku-band carrier. Time frame: March to June 2013 Baseline: 8300 km 14

15 Two-way satellite time and frequency transfer (TWSTFT) TWSTFT carrier phase between NICT (Japan) and PTB (Germany) Preliminary results: Intercontinental clock comparison using the phase information of the Ku-band carrier. Time frame: March to June 2013 Baseline: 8300 km 15

16 Two-way satellite time and frequency transfer (TWSTFT) Sources of Instabilites 16

17 New Experiments Broad bandwidth TWSTFT ITOC International Time Scales with Optical Clocks (EMRP Project) Project) Optical frequency comparisons using broad bandwidth TWSTFT (20 Mcps) Goal is a factor of ten improvement in stability compared to current state of the art satellitebased techniques. Campaign is scheduled for The ITOC project is part of the European Metrology Research Programme (EMRP). The EMRP is jointly funded by the EMRP articipating countries within EURAMET and the European Union. [H. Margolis et al., Proc. EFTF/IFCS 2013, Prague] 17

18 New Experiments ACES Atomic clock ensemble in space Time transfer with the ACES MWL link Acknowledgement: Thanks to Luigi Caciapuoti and Christophe Salomon for providing some material for this presentation. 18

19 New Experiments ACES microwave link 19

20 New Experiments ACES microwave link Examples for CV and ncv scenarios CV ncv 20

21 New Experiments ACES microwave link ation (s) Time devi PHARAO SHM MWL Averaging g time (s) 21

22 Time Scale Comparisons with ACES Site calibration Two fixed GTs are calibrated relatively to a mobile GT Step 1 Step 2 ACES time scale ACES time scale MWL FS MWL FS MWL GTi MWL GTM MWL GTj MWL GTM Ground time scale i Ground time scale j Step 3: repetition of step 1 In this configuration also differential delays between two GT are cancelled. Calibration including all constant systematic uncertainties. One mobile GT needs to be moved during the mission. 22

23 Time Scale Comparisons with ACES Link calibration One mobile GT is calibrated relatively to a fixed GT Step 1 Step 2 ACES time scale MWL FS ACES time scale MWL FS MWL GTi MWL GTM MWL GTM Ground time scale i Ground time scale j Step 3: repetition of step 1 In this configuration also differential delays between two GT are cancelled. Calibration including all constant systematic uncertainties One mobile GT needs to be moved during the mission 23

24 Two-way satellite time and frequency transfer (TWSTFT) Calibration Time transfer with an uncertainty at the level of 1 ns 24

25 Two-way satellite time and frequency transfer (TWSTFT) Calibration Calibration campaigns (in the TAI network) using a mobile station are being performed o far by: TUG (European laboratories) NICT (Japan and Asia) USNO (link to PTB) Example: Latest campaign USNO-PTB June

26 Two-way satellite time and frequency transfer (TWSTFT) Calibration Stability of the portable (and reference station) during the European campaigns E1: PS TUG ns E2: PS IEN ns PS IEN ns E3: PS PTB ns E4: PS PTB ns E5: PS TUG ns Reproducibility of TWSTFT calibrations Differential correction applied to the operational link based on the calibration result Error bars: estimated uncertainty Gray bars: link uncertainty based on past calibrations 26

27 Two-way satellite time and frequency transfer (TWSTFT) Calibration First link calibration with TimeTech st mobile station ti in November Involved Laboratories: TimeTech (TIM) Physikalisch-Technische Bundesanstalt (PTB) Obervatoire de Paris (OP) Federal Institute of Metrology (METAS) 27

28 Two-way satellite time and frequency transfer (TWSTFT) Calibration Scheme of main components and setup Fibre cable Equipment inside trailer 28

29 Calibration Uncertainty estimation 2 a, k 2 a, j 2 b,1 2 b,2 2 b,3 U = U + U + U + U + U. CALR 29

30 Two-way satellite time and frequency transfer (TWSTFT) Calibration Calibration values and uncertainties Campaigns Nov 2012 Mai 2013 Scheduled CH, OP, PTB, TIM AOS, ESTEC (ESA), VSL, TIM for 2013 INRIM, PTB, PTF1 (Galileo) 30

31 Two-way satellite time and frequency transfer (TWSTFT) Calibration VNIIFTRI-PTB campaign Oct-Nov 2012 Campaign conducted by VNIIFTRI employing three different techniques: 1) VNIIFTRI mobile TWSTFT station 2) Tranportable GNSS receiver TTS-3 3) Transportable passive hydrogen maser [Andrey Naumov and Yury Smirnov, VNIIFTRI] 31

32 Two-way satellite time and frequency transfer (TWSTFT) Calibration VNIIFTRI-PTB campaign Oct-Nov 2012 Campaign conducted by VNIIFTRI employing three different techniques: UTC(PTB) UTC(SU) ns Mobile Transportable GNSS receiver TWSTFT H-Maser TTS-3 station SU02 CH1-76A MJD MJD MJD u A u B u ) VNIIFTRI mobile TWSTFT station 2) Tranportable GNSS receiver TTS-3 3) Transportable passive hydrogen maser [Andrey Naumov and Yury Smirnov, VNIIFTRI] 32

33 Perspective of TWSTFT Independent of and thus complemantary to GNSS 1 ns accuracy has been demonstrated, USNO reported 0.4 ns rms reproducibility 20 Mcps experiment with current equipment possible with currently used equipment Carrier phase solution not yet implemented Improved TWSTFT and GNSS would be the proper means to support the ACES mission. Possibility to calibrate long distance fiber links for time transfer 33

34 Time transfer through optical fibers Local installations supporting MWL GT Other techniques e.g. laser links / VLBI MWL GT TWSTFT GPS H-maser Monitor facility UTC(k) frequency comb Fountain clocks Optical clocks Local distribution and monitor systems are necessary to ensure the required performance, e.g. to supply the MWL GT with a calibrated reference time point. 34

35 Time transfer through optical fibers Local installations supporting MWL GT 35

36 Time transfer through optical fibers Local installations supporting MWL GT Precision < 3000 s 36

37 Time transfer through optical fibers Time Transfer between IQ and PTB Optical fiber time transfer is limited by instability of PHM. GPS PPP common clock performance at PTB is slightly better than on the baseline Hannover-Braunschweig. a nsch eig 37

38 Time transfer through optical fibers Time Transfer between IQ and PTB UTC(PTB) - PHM Distance: 73 km optical fiber Time transfer through optical fibers + GPS PPP time transfer Double difference ns Noise of GPS PPP time transfer is dominant. 38

39 Time transfer through optical fibers Fiber link between GUM and AOS [L. Sliwczynski et al., Metrologia, 2013] 39

40 Time transfer through optical fibers Fiber links Other examples: Two-fiber timing transfer SP/Mikes/STUPI (Sweden/Finland) 570 km using SONET frame: dayly variation ~ a few ns, best stability (1 d) ~30 ps (submarine) Cesnet/IPE/Austria (Smotlacha et al) 550 km: stability (1 d)~1 ns [O. Lopez, Appl. Phys. B, 2012] 40

41 Time transfer through optical fibers Fiber links [W.-H. Tseng and H. T. Lin, NCSLI Measure J. Meas. Sci, 2013] 41

42 Time Scale Comparisons Ground-to-ground clock comparisons using different techniques: Comparison to established operational techniques: TWSTFT U ns (maximum baseline km) GNSS U < 1.6 ns (maximum baseline km, global) Optical fibers U 0.1 ns to 0.2 ns (baseline so far <1000 km) ACES U = 0.1 ns (prospective) Laser Ranging U = 0.05 ns (prospective) VLBI U =? 42

43 A global metrology network for time and frequency GNSS global backbone TWSTFT intercontinental links ASIA/USA EUR/USA ASIA/EUR ASIA AMC-2 T-11N AM-2 GE-23 ACES, Laser ranging, VLBI intercontinental links Continental otical fber networks Are intercontinental links possible? 43

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