The co-chairs of the meeting
Decoupling Civil Timekeeping from Earth Rotation received the
information described via a contributor.
We believe that
this PDF file
was produced from a copy of
ITU-R Document 7/1005-E.
That should be the draft revision of
Recommendation ITU-R TF.460-6 which is to be voted upon at the
Radiocommunication Assembly in Geneva in 2012 January.
The remainder of this file is a crude conversion of that
PDF file into HTML.
Radiocommunication Assembly (RA-12)
Geneva, 16-20 January 2012
Subject: Question ITU-R 236/7
Document 7/1005-E
20 October 2011
Radiocommunication Study Group 7
DRAFT REVISION OF RECOMMENDATION ITU-R TF.460-6
Standard-frequency and time-signal emissions
Summary of revisions
This modification of the Recommendation eliminates the procedure for adjustment of UTC by
insertion of leap seconds. The elimination of the leap second adjustments is recommended to be
effective on 1 January five years after approval of this Recommendation.
H:\WRC\RA\TF\R07-SG07-RP-1005!!MSW-E[1].DOCX (316069) 05.12.11 05.12.11
2
1/1005-E
DRAFT REVISION OF RECOMMENDATION ITU-R TF.460-6*
Standard-frequency and time-signal emissions
(Question ITU-R 102/7)
(1970-1974-1978-1982-1986-1997-2002)
Scope
This Recommendation defines the implementation of Coordinated Universal Time (UTC) without leap
second adjustments. UTC serves as the time and frequency reference of standard-frequency and time-signal
emissions.
The ITU Radiocommunication Assembly,
considering
a) that the World Administrative Radio Conference, Geneva, 1979, allocated theArticle 5
of the Radio Regulations allocates bands of frequencies 20 kHz +/- 0.05 kHz, 2.5 MHz +/- 5 kHz
(2.5 MHz +/- 2 kHz in Region 1), 5 MHz +/- 5 kHz, 10 MHz +/- 5 kHz, 15 MHz +/- 10 kHz, 20 MHz
+/- 10 kHz and 25 MHz +/- 10 kHz to the standard-frequency and time-signal service;
b) that additional standard frequencies and time signals are emitted in other frequency
bands;
cb) the provisions of Article 26 of the Radio Regulations;
dc) the continuing need for close cooperation between Radiocommunication Study Group 7
and the International Maritime Organization (IMO), the International Civil Aviation Organization
(ICAO), the General Conference of Weights and Measures (CGPM), the Consultative Committee
for Time and Frequency (CCTF), the Bureau International des Poids et Mesures (BIPM), the
International Earth Rotation and Reference Systems Service (IERS) and the concerned Unions of
the International Council of Scientific Unions (ICSU);
ed) the desirabilityimportance of maintaining worldwide coordination of standard-
frequency and time-signal emissions;
fe) the need to disseminate standard frequencies and time signals in conformity with the SI
(International System of Units) second as defined by the 13th General Conference of Weights and
Measures (1967)CGPM;
g) the continuing need to make universal time (UT) immediately available to an
uncertainty of one-tenth of a second,
f) that in 1975 the CGPM recommended the use of UTC as the basis of civil time;
_______________
* This Recommendation should be brought to the attention of the International Maritime
Organization (IMO), the International Civil Aviation Organization (ICAO), the General Conference
of Weights and Measures (CGPM), the Consultative Committee for Time and Frequency (CCTF),
the Bureau International des Poids et Mesures (BIPM), the International Earth Rotation and
Reference Systems Service (IERS), the International Union of Geodesy and Geophysics (IUGG),
the International Union of Radio Science (URSI), the International Organization for Standardization
(ISO) and the International Astronomical Union (IAU).
H:\WRC\RA\TF\R07-SG07-RP-1005!!MSW-E[1].DOCX (316069) 05.12.11 05.12.11
3
1/1005-E
g) that other scientific organizations, particularly the International Astronomical Union
(IAU) and the International Union of Radio Science (URSI), have recommended the general use of
UTC;
h) the importance of monitoring the difference between the UTC time-scale and the time
defined by the rotation of the Earth (UT1) and maintaining the respective knowledge-base;
j) that the IERS provides updated daily data relating the UT1 to UTC to users;
k) that the IERS provides predictions of the difference between UT1 and UTC at different
delays, which allow real-time access to UT1, and which will on average over a two-year period
provide a more accurate knowledge of UT1 than does UTC with leap seconds,
noting
that Recommendation ITU-R TF.460-6 is incorporated by reference in the Radio Regulations, and
that the revised Recommendation ITU-R TF.460 will become effective only after the date of entry
into force established by the appropriate World Radiocommunication Conference,
recognizing
1 that the World Administrative Radio Conference (Geneva, 1979) (WARC-79) has
decided that UTC shall be used in all international radiocommunication activities;
2 that according to Recommendation ITU-R TF.536 and in accordance with the
recommendation of the CGPM the designation of UTC is to be used in all languages;
3 that the UTC system with leap seconds was essentially introduced to provide a common
standard for broadcast time and frequency signals generated from the UTC(k) physical
representations and give ready access to low-precision UT1 from these broadcast times and
frequency signals maintained within the necessary approximation for celestial navigation;
4 that an increasing number of applications require traceability to a continuous
international time-scale;
5 that time references other than UTC that are proliferating do not offer the reliability,
accessibility, or metrological quality of the international reference UTC;
6 that celestial navigation is no longer a primary means of navigation;
7 that users can easily access UT1 information by means other than radio transmissions,
recommends
1 that all standard-frequency and time-signal emissions conform as closely as possible to
coordinated universal time (UTC) (see Annex 1); that the timethat UTC as defined in Annex 1
should be used to designate the time in all international telecommunication activities and in all
official documents of ITU;
2 that the application of leap second adjustments to UTC should cease on 1 January five
years after approval by the appropriate World Radiocommunication Conference;
3 that the UTC frequency should be used as the ultimate reference for standard-frequency
emissions;
4 that the transmission of time signals should not deviate from UTC by more than
1 ms100 microseconds;
5 that the emitted standard frequencies should not deviate by more than 1 part in 1010, and
1011 from the UTC frequency;
H:\WRC\RA\TF\R07-SG07-RP-1005!!MSW-E[1].DOCX (316069) 05.12.11 05.12.11
4
1/1005-E
6 that the time signals emitted from each transmitting station should bear a known relation
to the phase of the carrier;,
2 that standard-frequency and time-signal emissions, and other time-signal emissions
intended for scientific applications (with the possible exception of those dedicated to special
systems) should contain information on UT1 UTC and TAI UTC (see Annex 1).
invites
the IERS and the service providers of Global Navigation Satellite Systems to offer convenient
access to values of UT1-UTC so that users have access to UT1.
ANNEX 1
Time and Ttime -scales
A Universal time (UT1)
Universal time (UT) is the general designation of time scales based on the rotation of the Earth.
In applications in which an imprecision of a few hundredths of a second cannot be tolerated, it is
necessary to specify the form of UT which should be used:
UT0 is the mean solar time of the prime meridian obtained from direct astronomical
observation;
UT1 is UT0 corrected for the effects of small movements of the Earth relative to the axis of
rotation (polar variation);
UT2 is UT1 corrected for the effects of a small seasonal fluctuation in the rate of rotation of
the Earth;
UT1 is used in this Recommendation, since it corresponds directly with the angular position of
the Earth around its axis of diurnal rotation.
Concise definitions of the above termsUT1 is the time determined from astronomical observations
of the rotation of the Earth with respect to the International Celestial Reference System. A technical
description and the concepts involved are available in the publications of the IERS (Paris, France).
B International atomic time (TAI)
The international reference scale of atomic time (TAI), based on the SI second (SI), as realized on
the rotating geoid, is formed by the BIPM on the basis of clock data supplied by cooperating
establishments. It is in the form of a continuous scaletime, e.g. in days, hours, minutes and seconds
from the origin 1 January 1958 (adopted by the CGPM 1971). TAI is not physically realized and
consequently is not suitable for time dissemination.
C Coordinated universal time (UTC)
UTC is the time-scale maintained by the BIPM, with assistance from the IERS, which forms the
basis of a coordinated dissemination of standard frequencies and time signals. It corresponds
exactly in rate with TAI but differs from it by an integerintegral number of seconds.
H:\WRC\RA\TF\R07-SG07-RP-1005!!MSW-E[1].DOCX (316069) 05.12.11 05.12.11
5
1/1005-E
The UTC scale is adjusted by the insertion or deletion of seconds (positive or negative leap-
seconds) to ensure approximate agreement with UT1.
D DUT1
The value of the predicted difference UT1 - UTC, as disseminated with the time signals is denoted
DUT1; thus DUT1 UT1 - UTC. DUT1
NOTE 1 — The value UT1-UTC, either observed or predicted, is determined by the IERS and
disseminated by multiple sources. It may increase or decrease without limit. It may be regarded as a
correction to be added to UTC to obtain a better approximation to UT1.
NOTE 2 — The dissemination of the previously codedThe values of UT1-UTC will be
discontinuedDUT1 are given by the IERS in multiples of 0.1 s.
The following operational rules apply:
1 Tolerances
1.1 The magnitude of DUT1 should not exceed 0.8 s.
1.2 The departure of UTC from UT1 should not exceed 0.9 s (see Note 1).
1.3 The deviation of (UTC plus DUT1) should not exceed 0.1 s.
NOTE 1 — The difference between the maximum value of DUT1 and the maximum departure of
UTC from UT1 represents the allowable deviation of (UTC DUT1) from UT1 and is a safeguard
for the IERS against unpredictable changes in the rate of rotation of the Earth.
2 Leap-seconds
2.1 A positive or negative leap-second should be the last second of a UTC month, but first
preference should be given to the end of December and June, and second preference to the end of
March and September.
2.2 A positive leap-second begins at 23h 59m 60s and ends at 0h 0m 0s of the first day of
the following month. In the case of a negative leap-second, 23h 59m 58s will be followed one
second later by 0h 0m 0s of the first day of the following month (see Annex 3).
2.3 The IERS should decide upon and announce the introduction of a leap-second, such an
announcement to be made at least eight weeks in advance.
3 Value of DUT1
3.1 The IERS is requested to decide upon the value of DUT1 and its date of introduction
and to circulate this information one month in advance. In exceptional cases of sudden change in
the rate of rotation of the Earth, the IERS may issue a correction not later than two weeks in
advance of the date of its introduction.
3.2 Administrations and organizations should use the IERS value of DUT1 for standard-
frequency and time-signal emissions, and are requested to circulate the information as widely as
possible in periodicals, bulletins, etc.
3.3 Where DUT1 is disseminated by code, the code should be in accordance with the
following principles (except § 3.4 below):
H:\WRC\RA\TF\R07-SG07-RP-1005!!MSW-E[1].DOCX (316069) 05.12.11 05.12.11
6
1/1005-E
— the magnitude of DUT1 is specified by the number of emphasized second markers and
the sign of DUT1 is specified by the position of the emphasized second markers with
respect to the minute marker. The absence of emphasized markers indicates DUT1 = 0;
— the coded information should be emitted after each identified minute if this is
compatible with the format of the emission. Alternatively the coded information should
be emitted, as an absolute minimum, after each of the first five identified minutes in
each hour.
Full details of the code are given in Annex 2.
3.4 DUT1 information primarily designed for, and used with, automatic decoding
equipment may follow a different code but should be emitted after each identified minute if this is
compatible with the format of the emission. Alternatively, the coded information should be emitted,
as an absolute minimum, after each of the first five identified minutes in each hour.
3.5 Other information which may be emitted in that part of the time-signal emission
designated in § 3.3 and 3.4 for coded information on DUT1 should be of a sufficiently different
format that it will not be confused with DUT1.
3.6 In addition, UT1 - UTC may be given to the same or higher precision by other means,
for example, by messages associated with maritime bulletins, weather forecasts, etc.;
announcements of forthcoming leap-seconds may also be made by these methods.
3.7 The IERS is requested to continue to publish, in arrears, definitive values of the
differences UT1 - UTC and UT2 - UTC.
E DTAI
The value of the difference TAI - UTC, as disseminated with time signals, shall be denoted DTAI.
DTAI TAI UTC may be regarded as a correction to be added to UTC to obtain TAI.
The TAI UTC values are published in the BIPM Circular T. The IERS should announce the value
of DTAI in integer multiples of one second in the same announcement as the introduction of a
leap-second (see § D.2).
ANNEX 2
Code for the transmission of DUT1
A positive value of DUT1 will be indicated by emphasizing a number, n, of consecutive second
markers following the minute marker from second marker one to second marker, n, inclusive;
n being an integer from 1 to 8 inclusive.
DUT1 = (n x 0.1) s
A negative value of DUT1 will be indicated by emphasizing a number, m, of consecutive second
markers following the minute marker from second marker nine to second marker (8 + m) inclusive,
m being an integer from 1 to 8 inclusive.
DUT1 = (m x 0.1) s
A zero value of DUT1 will be indicated by the absence of emphasized second markers.
H:\WRC\RA\TF\R07-SG07-RP-1005!!MSW-E[1].DOCX (316069) 05.12.11 05.12.11
7
1/1005-E
The appropriate second markers may be emphasized, for example, by lengthening, doubling,
splitting or tone modulation of the normal second markers.
Examples:
FIGURE 1
DUT1 = + 0.5 s
Emphasized
Minute
second markers
marker
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Limit of coded sequence
0460-01
FIGURE 2
DUT1 = - 0.2 s
Minute
Emphasized
marker
second markers
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Limit of coded sequence
0460-02
ANNEX 3
Dating of events in the vicinity of a leap-second
The dating of events in the vicinity of a leap-second shall be effected in the manner indicated in the
following Figures:
H:\WRC\RA\TF\R07-SG07-RP-1005!!MSW-E[1].DOCX (316069) 05.12.11 05.12.11
8
1/1005-E
FIGURE 3
Positive leap-second
event
leap-second
Designation of the date of the event
56
57
58
59
60
0
1
2
3
4
30 June, 23h 59m 60.6s UTC
30 June, 23h 59m
1 July, 0h 0m
FIGURE 4
Negative leap-second
event
Designation of the date of the event
56
57
58
0
1
2
3
4
5
6
30 June, 23h 59m 58.9s UTC
30 June, 23h 59m
1 July, 0h 0m
0460-03
______________
H:\WRC\RA\TF\R07-SG07-RP-1005!!MSW-E[1].DOCX (316069) 05.12.11 05.12.11