On 2017-02-01 12:46 PM, Steve Allen wrote:
On Wed 2017-02-01T10:50:12 -0500, Brooks Harris hath writ:
https://www.itu.int/dms_pubrec/itu-r/rec/tf/R-REC-TF.460-6-200202-I!!MSW-E.doc
Section C Coordinated universal time (UTC) says "UTC is the
time-scale maintained by the BIPM, with assistance from the IERS..."
This says BIPM is the authority that maintains the UTC timescale,
doesn't it?
Yes, but that is a "grandfathered" arrangement with a history.
TF.460-6 is a rewrite from the original Rec. 460 which placed all
authority with the BIH (International Time Bureau).
In 1972 J. Terrien (the director of the BIPM who had been at the IAU
meetings on radio broadcast time signals since 1964) noted that "the
BIPM does no experimental work on the measurement of time and
frequency" and apologized that "regrettable misunderstandings,
especially between astronomers and physicists, have crept into
discussions on time and frequency."
That is to say that at the inception of leap seconds the BIPM
had no component which could have defined a time scale.
The advent of atomic chronometers made the role of the BIH unclear.
The precision of satellite and interferometric measurements of the
earth compounded this cloudiness. BIH had oversight of axial rotation
of earth, and two other agencies had oversight of the motion of the
pole of earth. That distinction made sense in 1920, but not by 1980.
The overseeing astronomical and geophysical agencies decided to
rearrange the divisions of responsibility beginning with 1988. BIH
and the two polar motion organizations were abolished. The atomic
chronometers went to BIPM. All of the earth orientation went under
the umbrella of IERS. The CCIR got reorganized into the ITU-R in
1992, the recommendations were not revised for years after that. None
of the agencies who currently have responsibility existed when all
this started, and the documents still do not quite describe how things
actually work.
Right, thanks. It is a fascinating history, if somewhat frustrating when
searching for a practical answer.
So, BIPM is the current authority of maintenance of TAI and UTC ("with
assistance from the IERS"), is that right? And IERS makes their
procedures for "assistance" known through the IERS Conventions?. And ITU
and Rec 460 is the authority for "Standard-frequency and time-signal
emission"? And Rec 460 points at BIPM Circular T.
As I read it there is, in fact, a chain of provenance through this even
though its not so obvious. Of course, as I said, I think the facts are a
scattered around and takes far to long to discover how it ties together,
and I wish I had more confidence in my conclusions.
What's your opinion of the TAI-UTC value update topic? At or after the
Leap Second?
-Brooks
--
Steve Allen <[email protected]> WGS-84 (GPS)
UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855
1156 High Street Voice: +1 831 459 3046 Lng -122.06015
Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m
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