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@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_bur...@iers.org >> To: messa...@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. > > _______________________________________________ > LEAPSECS mailing list > LEAPSECS@leapsecond.com > https://pairlist6.pair.net/mailman/listinfo/leapsecs >
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