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Review and Preview of Two-way Time Transfer for UTC - from TW S TT 1 to TW O TT 2 Bi-directional method is widely used in metrological measurements. By.

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Presentation on theme: "Review and Preview of Two-way Time Transfer for UTC - from TW S TT 1 to TW O TT 2 Bi-directional method is widely used in metrological measurements. By."— Presentation transcript:

1 Review and Preview of Two-way Time Transfer for UTC - from TW S TT 1 to TW O TT 2 Bi-directional method is widely used in metrological measurements. By the symmetric principle, systematical errors are largely cancelled. TWSTFT uses the reciprocated radio signals emitted by two ground laboratories through geo-satellite, the atmosphere delay effects are greatly reduced. TWOTFT is also based on the reciprocity in both the signals to balance the propagation path delays in the fibres. By investigating the historical documents and the latest developments, we briefly review and preview the two-way for UTC time transfers. Key words: UTC, TWSTFT, TWOTFT ID 520 EFTF2013 July Prague -Ongoing – present [2,3] -Oncoming- In the coming 5-10 years [3,4] Long-term goal: Compare the optical clocks ~10 day More than 14 UTC laboratories active Already operational UTC(AOS)-UTC(PL) Immediate Applications in UTC: - Validate the BIPM calibrator with u B ~ 100 ps by the fibre - Verify the accurate GNSS and TWSTFT techniques New challenges: - the theoretical issues - the practical issues: data processing, format, programs … II. Optical Fibre Reciprocity D AB = D BA in Two-Way time transfer 1.Two-Way Satellite Time Transfer; 2. Two-Way Optical-fibre Time Transfer Z. Jiang, H. Konaté and W. Lewandowski Time Department, Bureau International des Poids et Mesures (BIPM) Pavillon de Breteuil F-92312, SÈVRES CEDEX, France -Early history [1,3] 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 ) and B (u B ) uncertainties were near 10~100 ns and 100~1000 ns respectively 1970s ATS-1, 1983 Intelsat-V: u A reached 0.2 ns level. RELAY 196x Communication Satellite TELSTAR st Active Communication Satellite ECHO-I first Passive Communication Satellite NASA images Report to the 5th TW WG in 1997 (hand-writing transparent slides probably from PTB) [2] Conclusion: TWSTFT Earth-stations can be monitored to be stable to a: *TDEV of 100 ps for τ=24h-1200h (1d to 50d) * Freq. transfer at at τ =1 day Hardware technology developments reduced the costs and dimensions of the devices. UTC Labs could equip more automated and operational timing transfer system. Since 1987, NIST, USNO, NRC, TUG, NPL, NMi, VSL DTAG, PTB and OCA etc., began to perform routine experiments of three measurements per week using commercial Ku-band satellites. The declaration of 11th CCDS/CCTF (1989) encouraged the use of TWSTT and suggested to create at BIPM an ad-hoc working group on TWSTT. In 1992, several commercial satellite systems were available, and modems adapted for the technique were commercialized. In March 1993, the BIPM ad-hoc Working Group was transformed to the permanent CCDS/CCTF Working Group on TWSTFT. Then the TDEV of hundred ps was attainable. ITU (Internat. Telecommunication Union), approved in 1995 the standard data format for TWSTFT. The first TWSTT link officially introduced in the UTC was TUG-PTB in Circular T 139 published on the 17 August GPS therefore finished its solo role for UTC time link for more than a decade. 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 2005 The high accurate Europe-Asia transcontinental link between NICT and PTB was established in 2005 Establishment of the devices at PTB in 2005 at NICT Mobile TW calibrators The UTC links must be calibrated. Several calibration campaigns were organized in and between Europe, America and Asia. Calibration PeriodLaboratories/campaigns May-June 2003IT-PTB-IT July 2004PTB-OP-NPL-VSL-PTB Oct.-Nov. 2005PTB-SP-VSL-NPL-OP-IT-PTB May-June 2006TUG-PTB-CH-TUG Sept.-Oct. 2008PTB-NPL-OP-IT-VSL-CH-TUG PTB,OP,SP,CH,AOS … The diurnals and the data missing are well repaired in the combined link. The Tdev is greatly improved Combination of TW and GPS The symmetry in the two-way transfer when the signals go through atmosphere or optical fibre D AB D BA Lab A /T A Lab B /T B Network TWSTT Europe CH PTB OP VSL ROA USNO NIST SP IT Asia- America Y axis unit – ns X axis unit – UTC On MJD The real-time clock comparison between UTC(AOS) and UTC(PL) through a fibre link, First Operational Optical Fibre Time Link 420 km between UTC Laboratories AOS-PL Combined uncertainty 112 ps [4] 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 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 * --- 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 It is suggested adapting the ITU TWSTFT data format for TWOTFT [4]. Hence all the data exchanges, processing, calibrations, computations and the related methodology can be kept with only slight modifications. This will save huge time and man powers and speed up its applications. TL 25 km fibre experiment at TL [4] Acknowledgement and Reference We thank all TW labs for their contributions to UTC and to this paper 1.http://tycho.usno.navy.mil/twstt_hi.html, history of TWSTFThttp://tycho.usno.navy.mil/twstt_hi.html 2.http://www.bipm.org/wg/AllowedDocuments.jsp, documents of CCTF WG on TWSTFT back to 1989http://www.bipm.org/wg/AllowedDocuments.jsp 3.Z. Jiang, H. Konaté and W. Lewandowski 2013 TM220, Review and preview of Two-Way Time and Frequency Transfer for UTC generation -history, present and future 4.Śliwczyński Ł., Krehlik P., Czubla A., Buczek Ł., Lipiński M.: Dissemination of time and RF frequency via stabilized fibre optic link over the distance of 420 km, Metrologia, vol. 50, pp , 2013 Summary TWOTFT, with a combined uncertainty of an order of hundred ps level, would provoke fundamental changes in the UTC construction. E.g. TWOTT requires a few instant to calibrate a satellite time link with 100 ps uncertainty. Another example, the configuration of the international UTC time transfer network. Since more than three decades, the UTC generation has been using the space-techniques. A new era of the ground based techniques is returning … I. Use of Carrier phase and DPN The current TWSTFT observable is only the code. It is affected by measurement noise and diurnals hence limits in the accuracy. Further improvements should come from other observables, such as the DPN (dual pseudo-random noise) and Carrier Phase. MDev of DPN, TW CP, TW code, GPS CP vs. a Hydrogen Maser. The DPN allows doubly reducing the measurement uncertainty, in particular that from the diurnals. Because the resolution of the carrier phase is 100 to 1000 times more precise than that of the code, TWSTFT carrier phase transfer may reach a stabilities of 0.1 ps in time and or in frequency. Principle of TWTT The third author at the CCTF TW WG 6 th meeting San Fernando, October 1998


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