Judah Levine, Pulsar-Timing-2005: 1

Coordinated Universal Time Coordinated Universal Time (UTC)(UTC)

Judah LevineJudah Levine

JILA –- Time and Frequency JILA –- Time and Frequency Div.Div.

NIST and Univ. of ColoradoNIST and Univ. of Colorado

Boulder, Colorado 80309Boulder, Colorado 80309

Jlevine@boulder.nist.govJlevine@boulder.nist.gov

Judah Levine, Pulsar-Timing-2005: 2

Outline of the talkOutline of the talk

Definition of atomic time and UTCDefinition of atomic time and UTC BIPM computation of UTC, TAI, …BIPM computation of UTC, TAI, … Realization of UTC(lab) at timing Realization of UTC(lab) at timing

laboratorylaboratory Time transfer from a timing labTime transfer from a timing lab What should a user do with What should a user do with

calibration data?calibration data?

Judah Levine, Pulsar-Timing-2005: 3

Definition of civil time scaleDefinition of civil time scale

Civil TimeCivil Time

Atomic clocksLength of day

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Post-1972 definition of UTCPost-1972 definition of UTC Duration of second defined by Duration of second defined by unperturbedunperturbed cesium hyperfine cesium hyperfine transition on the rotating geoid:transition on the rotating geoid:

9,192,631,770 cycles 9,192,631,770 cycles 1 second 1 second Atomic-time day is 24Atomic-time day is 24606060= 86400 60= 86400

ss Astronomical day defined by UT1Astronomical day defined by UT1 ““Leap Seconds” added to UTC to keepLeap Seconds” added to UTC to keep

UT1- UTC UT1- UTC < 0.9 s< 0.9 s The times they are a-changingThe times they are a-changing

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Not confusing enough yet?Not confusing enough yet?

Resolution S2 (1996) of the Resolution S2 (1996) of the Consultative Committee for the Consultative Committee for the Definition of the Second (CCDS):Definition of the Second (CCDS):– Apply black-body correction to Apply black-body correction to

primary frequency standards.primary frequency standards.• Correction for a room-temperature Correction for a room-temperature

standard is about 2standard is about 21010-14-14 or about 0.6 or about 0.6 s/yrs/yr

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A clock ensemble – NIST styleA clock ensemble – NIST style

Clk 1 Clk 2 Clk 3 Clk 4 Clk n

WeightedAverage

(AT1 scale)

Steering basedon BIPM data(Circular T)

UTC(NIST)To services

Clock datato BIPM

PhaseStepper

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The role of the BIPMThe role of the BIPM

Lab 1 Lab 2 Lab 3 Lab 4 Lab 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 =>

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The questions …The questions …

How well do TAI and UTC realize How well do TAI and UTC realize the definition of the SI second?the definition of the SI second?

The BIPM has no clocksThe BIPM has no clocks– TAI and UTC are post-processed TAI and UTC are post-processed

paper scalespaper scales• TTBIPM is post-post-processed TAI scaleTTBIPM is post-post-processed TAI scale

– Realization of UTC is only via Realization of UTC is only via UTC(lab)UTC(lab)

– How well does UTC(lab) track UTC?How well does UTC(lab) track UTC?

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Comparison of Primary Standards

^ Feb. 1997 Dec. 2001^

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(MJD = Modified Julian Date)

T A I v s P rim ary S tan d a rd s

5 1 4 0 0 5 1 8 0 0 5 2 2 0 0 5 2 6 0 0 5 3 0 0 0 5 3 4 0 0

M JD (d a y s)

-3 0

-2 5

-2 0

-1 5

-1 0

-5

0

5

1 0

(

10-1

5 )

N IS T -F 1

N IS T -7

P T B -C S F 1

P T B -C S 2

IE N -C S F 1

N P L -C sF 1

S Y R T E - F O 2

S Y R T E -F O M

ta ivsp ff.g rf

.

Jan. 1 , 2000 Jan. 1, 2005

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2.510-14

(Gerard Petit, PTTI, 2003)

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10-14

(Gerard Petit, PTTI, 2003)

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10-15

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The common-view methodThe common-view method

Receiver

Transmitter

Receiver

Measure time differences and subtract,attenuates common-mode errors (SV clock,ionosphere, radial position, …

GPS satellite =>

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Common View, Arecibo-NIST

-600

-400

-200

0

200

400

600

800

1000

1200

52650 52700 52750 52800 52850 52900 52950 53000

MJD

Tim

e D

iffer

ence

(ns)

Dec,2003Dec,2002

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Common View, Arecibo-NIST

-800

-600

-400

-200

0

200

400

600

800

1000

1200

1400

53000 53100 53200 53300 53400 53500 53600

MJD

Tim

e di

ffere

nce

(ns)

2.310-14

Jan, 2004 July, 2005