[LEAPSECS] Fwd: IERS Message No. 354: Recent changes to the IERS 14 C04 series / Bulletin B

Tue May 8 11:09:42 EDT 2018

In short, they used some bad values without realizing it, then followed a
process that was flawed that amplified the bad values. Someone noticed the
small, but accumulating error and they've updated their process and re-run
the numbers.

Did I miss something?

Warner

On Tue, May 8, 2018 at 8:28 AM, Michael.Deckers via LEAPSECS <
leapsecs at leapsecond.com> wrote:

>
>
> 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_bureau at iers.org
>> To:     messages at iers.org
>>
>>
>>
>> ************************************************************************
>> IERS Message No. 354                                        May 07, 2018
>> ************************************************************************
>>
>>
>> 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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