Review and Preview of Two-way Time Transfer for

Review and Preview of Two-way Time Transfer for UTC 1 2 - from TWSTT to TWOTT -Oncoming- The third author at the CCTF TW WG 6 th meeting San Fernando, 29 - 30 October 1998 1. Two-Way Satellite Time Transfer; 2. Two-Way Optical-fibre Time Transfer In the coming 5 -10 years [3, 4] Z. Jiang, H. Konaté and W. Lewandowski Time Department, Bureau International des Poids et Mesures (BIPM) Pavillon de Breteuil F-92312, SÈVRES CEDEX, France zjiang@bipm. org Principle of TWTT 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. The symmetry in the two-way transfer when the signals go through atmosphere or optical fibre DAB 1999 – present [2, 3] DBA Lab. B/TB Lab. A /TA ITU (Internat. Telecommunication Union), approved in 1995 the standard data format for TWSTFT. 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. 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 10 -12@1 s or 10 -16@1 -day in frequency. MDev of DPN, TW CP, TW code, GPS CP vs. a Hydrogen Maser. -Ongoing- Reciprocity DAB = DBA in Two-Way time transfer The first TWSTT link officially introduced in the UTC was TUG-PTB in Circular T 139 published on the 17 August 1999. 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. TWOTFT is also based on the reciprocity in both the signals to balance the propagation path delays in the fibres. II. Optical Fibre By investigating the historical documents and the latest developments, we briefly review and preview the two-way for UTC time transfers. • Long-term goal: Compare the optical clocks ~10 -18@one 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: - theoretical issues - the practical issues: data processing, format, programs … Key words: UTC, TWSTFT, TWOTFT -Early history- The international UTC time link network in 2000 TW links in/between Asia, Europe and America in 2005 1960 -1997 [1, 3] ECHO-I first Passive Communication Satellite NASA images Mobile TW calibrators The UTC links must be calibrated. Several calibration campaigns were organized in and between Europe, America and Asia. Laboratories/campaigns May-June 2003 IT-PTB-IT July 2004 PTB-OP-NPL-VSL-PTB Oct. -Nov. 2005 PTB-SP-VSL-NPL-OP-IT-PTB May-June 2006 TUG-PTB-CH-TUG Sept. -Oct. 2008 Y axis unit – ns X axis unit – UTC On MJD 56454 PTB-NPL-OP-IT-VSL-CH-TUG PTB, OP, SP, CH, AOS … Combination of TW and GPS The diurnals and the data missing are well repaired in the combined link. The Tdev is greatly improved Conclusion: TWSTFT Earth-stations can be monitored to be stable to a: *TDEV of 100 ps for τ=24 h-1200 h (1 d to 50 d) * Freq. transfer at 2. 10 -15 at τ =1 day Report to the 5 th TW WG in 1997 (hand-writing transparent slides probably from PTB) [2] 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. at NICT The real-time clock comparison between UTC(AOS) and UTC(PL) through a fibre link, www. optime. org. pl/node/47 The high accurate Europe-Asia transcontinental link between NICT and PTB was established in 2005 TL 25 km fibre experiment at TL [4] 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. NIST PTB OP USNO VSL ROA IT Acknowledgement and Reference We thank all TW labs for their contributions to UTC and to this paper 1. 2. 3. 4. for statistical terms ESDVAR 0. 1 ps 1035000 X 1035000 X ESIG TMP HUM 0. 1 ps C % 2800 X 12 98 2800 X 12 98 PRES mbar 1013 1013 Summary TWOTFT, with a combined uncertainty of an order of SP CH The declaration of 11 th 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. Table 7. 2 The first 25 lines of the proposed TW%TFT data file T%PTB 56. 150 in unit ns for delay and ps * tfptb 56. 150 * FORMAT 01 * LAB PTB * REV DATE 2011 -08 -03 * ES PTB 01 LA: N 52 17 49. 787 LO: E 10 27 37. 966 HT: 143. 41 m * REF-FRAME ITRF * LINK 14 fibre: Dark Channel Length: 420. 00 Km Amplifiers: 6 * OPTICAL-TX: 1552. 1500 nm RX: 1552. 1550 nm * MODEM: Dedicated hardware SIGNAL: 1 PPS on square wave * Link Stabilization: YES * LINK 16 fibre: AAA Network Length: 72. 00 Km Amplifiers: 0 * OPTICAL-TX: 1542. 1000 nm RX: 1542. 1500 nm * MODEM: SATRE 037 SIGNAL: PRN, 20 Mcps * Link Stabilization: NO * CAL xxx TYPE: CAL xxx BRIDGED MJD: 55769 EST. UNCERT. : x. xxx ns * CAL 214 TYPE: CAL 141 BRIDGED MJD: 55769 EST. UNCERT. : 5. 000 ns * CAL 213 TYPE: CAL 142 BRIDGED MJD: 55769 EST. UNCERT. : 1. 300 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 * LOC REM hhmmss s 0. 1 ps PTB 01 TIM 01 14 56150 000400 119 265739347023 X 1226 X 120 119 000040870 X 0020 X 999 9 99999 PTB 01 14 56150 000700 119 266718670995 X 2491 X 120 119 000040870 X 0020 X 999 9 99999 PTB 01 OCA 01 14 56150 001000 119 264311268059 X 1497 X 120 119 000040870 X 0020 X 999 9 99999 PTB 01 IT 02 14 56150 001300 119 264702466195 X 1937 X 120 119 000040870 X 0020 X 213 1 479209 X PTB 01 ROA 01 14 56150 001600 119 260338922342 X 2520 X 120 119 000040870 X 0020 X 217 1 298673 X 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. Asia. America Calibration Period 2012 -2013 As a promising accurate time transfer technique , TWSTT started its experiments earlier than GNSS. -1960 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) -1965 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 1970 s ATS-1, 1983 Intelsat-V: u. A reached 0. 2 ns level. Europe TELSTAR 1962 Active Communication Satellite RELAY 196 x Communication Satellite Establishment of the devices at PTB in 2005 Network TWSTT 1 st First Operational Optical Fibre Time Link 420 km between UTC Laboratories AOS-PL Combined uncertainty 112 ps [4] 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 … http: //tycho. usno. navy. mil/twstt_hi. html, history of TWSTFT http: //www. bipm. org/wg/Allowed. Documents. jsp, documents of CCTF WG on TWSTFT back to 1989 Z. Jiang, H. Konaté and W. Lewandowski 2013 TM 220, Review and preview of Two-Way Time and Frequency Transfer for UTC generation -history, present and future 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. 133 -145, 2013 ID 520 EFTF 2013 July Prague