Coordinated Universal Time UTC Judah Levine JILA Time

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Coordinated Universal Time (UTC) Judah Levine JILA –- Time and Frequency Div. NIST and

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: 1

Outline of the talk Definition of atomic time and UTC n BIPM computation of

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

Definition of civil time scale Length of day Atomic clocks Civil Time Judah Levine,

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

Post-1972 definition of UTC n Duration of second defined by unperturbed cesium hyperfine transition

Post-1972 definition of UTC n 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 n Astronomical day defined by UT 1 n “Leap Seconds” added to UTC to keep UT 1 - UTC < 0. 9 s n The times they are a-changing n Judah Levine, Pulsar-Timing-2005: 4

Not confusing enough yet? n Resolution S 2 (1996) of the Consultative Committee for

Not confusing enough yet? n Resolution S 2 (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 Judah Levine, Pulsar-Timing-2005: 5

A clock ensemble – NIST style Clk 1 Clk 2 Clock data to BIPM

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

The role of the BIPM Lab 1 Lab 2 Lab 3 Lab 4 Lab

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

The questions … How well do TAI and UTC realize the definition of the

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

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

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

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

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

2. 5 10 -14 (Gerard Petit, PTTI, 2003) Judah Levine, Pulsar-Timing-2005: 11

2. 5 10 -14 (Gerard Petit, PTTI, 2003) Judah Levine, Pulsar-Timing-2005: 11

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

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

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

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

The common-view method GPS satellite => Receiver Transmitter Receiver Measure time differences and subtract,

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

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

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

2. 3 10 -14 Jan, 2004 July, 2005 Judah Levine, Pulsar-Timing-2005: 18

2. 3 10 -14 Jan, 2004 July, 2005 Judah Levine, Pulsar-Timing-2005: 18