On 2018-05-07 12:41, Rob Seaman wrote:
Anybody have more details about this? How it happened or what it might
mean for practical timekeeping?
Rob
--
-------- Forwarded Message --------
Subject: IERS Message No. 354: Recent changes to the IERS 14 C04
series / Bulletin B
Date: Mon, 7 May 2018 10:57:14 +0200 (CEST)
From: central_bur...@iers.org
To: messa...@iers.org
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IERS Message No. 354 May 07, 2018
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Recent changes to the IERS 14 C04 series / Bulletin B
Dear IERS users,
From its production in February 2017, 14 C04 nutation was only based
upon the IVS combined solution according to a recommendation issued by
representatives of IVS and IERS. But, on March 3, 2018 it turned out
that IVS combined solution had not been updated since January 13, when
Bulletin B was made. So, celestial pole offsets (CPO) were set to zero
after this date.
In order to fix this problem, on March 3 we run again the C04
combination by taking all VLBI solutions, of which the last UT1/CPO
determination went back to February 12. So we had to update the C04
series from January 13. With this new solution, the pole coordinates and
UT1-UTC were slightly changed.
There was a also a serious flaw in UT1 values till January 2018, where
UT1 intensive values are no more accounted after we wrongly follow an
advise of an IVS/IERS representative. Because of the error
interpolation, UT1 solution was seriously downgraded between IVS dates.
Whereas the precision of UT1 intensive is about 30 micros (against 10
micros for R1/R4 UT1), the error introduced by interpolation between two
IVS dates is probably much larger. We came to this conclusion, after
Frank Reinquin (CNES) put forward an anomalous increase of SLR LAGEOS
1/2 orbital residuals using the 14 C04. Then we discovered that these
anomalies were precisely located at the dates where UT1 intensive had
been ignored, and replaced by a pure interpolated values between
neighbouring R1/R4 sessions.
According to the decision of the IERS Directing Board of April 8, 2018
the 14 C04 solution for UT1 was modified on April 16, 2018 by including
the contribution of UT1 intensive back to 1996. The old version, updated
until 2018/04/16 was put in the directory
ftp://hpiers.obspm.fr/iers/eop/eopc04/eopc04.2017/.
I am just guessing what is meant. Here is my tentative
de-Frenchification:
[From its production in|Since] February 2017, [|the] 14 C04
nutation
[|data for the deviation of the observed celestial
intermediate pole CIP
from the pole of the 2006 nutation series] was [only based
upon|derived
only from] the IVS combined solution [|for the CIP,]
[according to|following]
a recommendation issued by representatives of IVS and IERS.
[But,|Also,] on March 3, 2018 when Bulletin B [|for 2018
February] was made
it [turned out|was discovered] that [|the] IVS combined
solution had not
been [updated since|kept up to date after] January 13. So,
celestial pole
offsets (CPO) were [set to|determined to be] zero after
this date [|2018-02-13].
In order to fix this problem, on March 3 we [run|ran] again
the C04
combination by taking all VLBI solutions, of which the last
UT1/CPO
determination went back to February 12. So we had to update
the C04
series from January 13 [|onwards]. With this new solution,
the pole
coordinates and UT1-UTC were slightly changed.
There [was a also|also has occurred] a serious flaw in UT1
values
[till|before] January 2018, where UT1 [intensive
values|values derived
from intensive VLBS observations] [are no more
accounted|were no longer
taken into account] after we wrongly follow[|ed] an
[advise|advice]
of an IVS/IERS representative. Because of [the error|this
erroneous]
interpolation, [|the] UT1 solution was seriously
[downgraded|degraded in]
between IVS dates.
Whereas the [precision|uncertainty] of UT1 [intensive|data
taken from
intensive VLBR observations] is about 30 micros[|econsds]
([against|as opposed to]
10 micros[|econds] for R1/R4 UT1), the error introduced by
interpolation
between two IVS dates is probably much larger. We came to
this conclusion, after
Frank Reinquin (CNES) put forward [|evidence of] an
anomalous increase of SLR LAGEOS
1/2 orbital residuals [using|with respect to] the 14 C04
[series]. Then we
discovered that these anomalies were precisely located at
the dates
where UT1 intensive[|s] had been ignored, and [|had been]
replaced by
[a pure interpolated|] values [between|interpolated solely
from]
neighbouring R1/R4 sessions.
According to [the|a] decision of the IERS Directing Board
of April 8, 2018
the 14 C04 solution for UT1 was modified on April 16, 2018
by including
the contribution [of|to] UT1 [intensive|deduced from
intensive VLBR observations]
back [to|since] 1996. The old version, [updated|computed]
until [2018/04/16|2018-04-15]
was put in the directory
ftp://hpiers.obspm.fr/iers/eop/eopc04/eopc04.2017/.
Michael Deckers.
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