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Coordinated Universal Time (UTC)

Coordinated Universal Time (UTC). Judah Levine JILA –- Time and Frequency Div. NIST and Univ. of Colorado Boulder, Colorado 80309 Jlevine@boulder.nist.gov. Outline of the talk. Definition of atomic time and UTC BIPM computation of UTC, TAI, … Realization of UTC(lab) at timing laboratory

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Coordinated Universal Time (UTC)

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  1. Coordinated Universal Time (UTC) Judah Levine JILA –- Time and Frequency Div. NIST and Univ. of Colorado Boulder, Colorado 80309 Jlevine@boulder.nist.gov

  2. Outline of the talk • Definition of atomic time and UTC • BIPM computation of UTC, TAI, … • Realization of UTC(lab) at timing laboratory • Time transfer from a timing lab • What should a user do with calibration data?

  3. Definition of civil time scale Length of day Atomic clocks Civil Time

  4. Post-1972 definition of UTC • Duration of second defined by unperturbed cesium hyperfine transition on the rotating geoid: 9,192,631,770 cycles  1 second • Atomic-time day is 246060= 86400 s • Astronomical day defined by UT1 • “Leap Seconds” added to UTC to keep UT1- UTC < 0.9 s • The times they are a-changing

  5. Not confusing enough yet? • Resolution S2 (1996) of the Consultative Committee for the Definition of the Second (CCDS): • Apply black-body correction to primary frequency standards. • Correction for a room-temperature standard is about 210-14 or about 0.6 s/yr

  6. A clock ensemble – NIST style Clk 1 Clk 2 Clk 3 Clk 4 Clk n Weighted Average (AT1 scale) Phase Stepper Clock data to BIPM Steering based on BIPM data (Circular T) UTC(NIST) To services

  7. The role of the BIPM Lab 1 Lab 2 Lab 3 Lab 4 Lab n EAL: Weighted average of 250 clocks Stability => Add fountain data: TAI Accuracy => Add UT1 data: UTC Astronomy => Circular T (monthly) gives UTC-UTC(lab) for every lab

  8. The questions … • How well do TAI and UTC realize the definition of the SI second? • The BIPM has no clocks • TAI and UTC are post-processed paper scales • TTBIPM is post-post-processed TAI scale • Realization of UTC is only via UTC(lab) • How well does UTC(lab) track UTC?

  9. Comparison of Primary Standards ^ Feb. 1997 Dec. 2001^

  10. (MJD = Modified Julian Date)

  11. 2.510-14 (Gerard Petit, PTTI, 2003)

  12. 10-14 (Gerard Petit, PTTI, 2003)

  13. 10-15

  14. The common-view method GPS satellite => Transmitter Receiver Receiver Measure time differences and subtract, attenuates common-mode errors (SV clock, ionosphere, radial position, …

  15. Dec,2002 Dec,2003

  16. 2.310-14 July, 2005 Jan, 2004

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