# Judah Levine, Pulsar-Timing-2005: 1 Coordinated Universal Time (UTC) Judah Levine JILA –- Time and Frequency Div. NIST and Univ. of Colorado Boulder, Colorado.

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Judah Levine, Pulsar-Timing-2005: 1 Coordinated Universal Time (UTC) Judah Levine JILA –- Time and Frequency Div. NIST and Univ. of Colorado Boulder, Colorado 80309 Jlevine@boulder.nist.gov

Judah Levine, Pulsar-Timing-2005: 2 Outline of the talk Definition of atomic time and UTC Definition of atomic time and UTC BIPM computation of UTC, TAI, … BIPM computation of UTC, TAI, … Realization of UTC(lab) at timing laboratory Realization of UTC(lab) at timing laboratory Time transfer from a timing lab Time transfer from a timing lab What should a user do with calibration data? What should a user do with calibration data?

Judah Levine, Pulsar-Timing-2005: 3 Definition of civil time scale Civil Time Atomic clocksLength of day

Judah Levine, Pulsar-Timing-2005: 4 Post-1972 definition of UTC Duration of second defined by unperturbed cesium hyperfine transition on the rotating geoid: 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 Atomic-time day is 24  60  60= 86400 s Astronomical day defined by UT1 Astronomical day defined by UT1 “Leap Seconds” added to UTC to keep “Leap Seconds” added to UTC to keep  UT1- UTC  < 0.9 s  UT1- UTC  < 0.9 s The times they are a-changing The times they are a-changing

Judah Levine, Pulsar-Timing-2005: 5 Not confusing enough yet? Resolution S2 (1996) of the Consultative Committee for the Definition of the Second (CCDS): 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/yrCorrection for a room-temperature standard is about 2  10 -14 or about 0.6  s/yr

Judah Levine, Pulsar-Timing-2005: 6 A clock ensemble – NIST style Clk 1Clk 2Clk 3Clk 4Clk n Weighted Average (AT1 scale) Steering based on BIPM data (Circular T) UTC(NIST) To services Clock data to BIPM Phase Stepper

Judah Levine, Pulsar-Timing-2005: 7 The role of the BIPM Lab 1Lab 2Lab 3Lab 4Lab n EAL: Weighted average of 250 clocks Circular T (monthly) gives UTC-UTC(lab) for every lab Add fountain data: TAI Add UT1 data: UTC Stability => Accuracy => Astronomy =>

Judah Levine, Pulsar-Timing-2005: 8 The questions … How well do TAI and UTC realize the definition of the SI second? How well do TAI and UTC realize the definition of the SI second? The BIPM has no clocks The BIPM has no clocks –TAI and UTC are post-processed paper scales TTBIPM is post-post-processed TAI scaleTTBIPM is post-post-processed TAI scale –Realization of UTC is only via UTC(lab) –How well does UTC(lab) track UTC?

Judah Levine, Pulsar-Timing-2005: 9 Comparison of Primary Standards ^ Feb. 1997Dec. 2001^

Judah Levine, Pulsar-Timing-2005: 10 (MJD = Modified Julian Date)

Judah Levine, Pulsar-Timing-2005: 11 2.5  10 -14 (Gerard Petit, PTTI, 2003)

Judah Levine, Pulsar-Timing-2005: 12 10 -14 (Gerard Petit, PTTI, 2003)

Judah Levine, Pulsar-Timing-2005: 13 10 - 15

Judah Levine, Pulsar-Timing-2005: 14 The common-view method Receiver Transmitter Receiver Measure time differences and subtract, attenuates common-mode errors (SV clock, ionosphere, radial position, … GPS satellite =>

Judah Levine, Pulsar-Timing-2005: 15 Two-way method Station 2Station 1 Limitation is delay asymmetry

Judah Levine, Pulsar-Timing-2005: 16 Two-way Satellite time transfer Modem TIC 1/s out 1/s in TIC in 1/s f up =14.3GH z f dn =12 GHz

Judah Levine, Pulsar-Timing-2005: 17 Dec,2003 Dec,2002

Judah Levine, Pulsar-Timing-2005: 18 2.3  10 -14 Jan, 2004 July, 2005

Judah Levine, Pulsar-Timing-2005: 19 4  10 -14

Judah Levine, Pulsar-Timing-2005: 20

Judah Levine, Pulsar-Timing-2005: 21

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