IGb08的来历：

自2009.05以来的不连续现象，现在有大量IGS08台站不可用于操作参考系对齐。特别是，IGS08核心网络最近已降至约50个可用站点，在南美，非洲和东亚留下大量漏洞。这个情况导致我们提议更新IGS08，名为IGb08。

以下为引用文字：

Dear IGS colleagues,

Either because they are decommissioned, dormant or have been affected by

discontinuities since 2009.5, a large number of IGS08 stations are now

unusable for operational reference frame alignments. In particular, the

IGS08 core network has dropped to about 50 usable stations recently,

leaving large holes in South America, Africa, and Eastern Asia. This

situation led us to propose an update of IGS08, called IGb08.

IGb08 mainly includes new sets of coordinates for 33 IGS08 stations having

been affected by position discontinuities since 2009.5, and 3 new stations

co-located with decommissioned IGS08 stations. (The various changes from

IGS08 to IGb08 are described in more details below.) All in all, this

update will increase the number of usable Reference Frame stations by

about 36 and the number of usable core stations by about 15.

IGb08.snx is available with some ancillary files at

ftp://igs-rf.ign.fr/pub/IGb08 & ftp://igs-rf.ensg.eu/pub/IGb08 :

* IGb08.snx           : IGb08 SINEX file

* IGb08.ssc           : IGb08.snx without covariance matrix

* IGb08_core.txt      : list of IGb08 core stations

* IGS08-IGb08.xls     : summary table of the IGS08->IGb08 changes

* IGS08-IGb08.dat     : numerical values of the IGS08->IGb08 changes

* IGb08_1701.png      : state map of the IGb08 network on week 1701

* IGb08_core_1701.png : state map of the IGb08 core network on week 1701

IGb08 will officially replace IGS08 starting with products of GPS week

1709 (7 October 2012). This switch aims at stabilizing the reference frame

alignment of the IGS products and should not lead to any particular

inconvenience for users.

Paul Rebischung, on behalf of the IGS Reference Frame Working Group

1) Introduction of post-discontinuity coordinates

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38 IGS08 stations with discontinuities since 2009.5 were first identified

as "repairable". A special cumulative solution was then formed, based on

the igb/igs weekly solutions up to week 1701, in which station annual

motions were estimated together with their positions and velocities.

Empirical offsets from the pre-break to the post-break station positions

were derived from this cumulative solution and used to introduce

post-break coordinates for the 38 stations in IGb08.

As a validation, IGb08 was used to align the igs weekly solutions of weeks

1632-1701. A check of the alignment residuals for the 38 newly introduced

points led us to reject 5 of them from IGb08 (BAN2, DGAR, GUUG, HOLB,

OHI3).

2) Intro. of new stations co-located with decommissioned IGS08 stations

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3 pairs of decommissioned IGS08 stations co-located with currently active

stations were identified (CHAT/CHTI, MALI/MAL2, NOUM/NRMD). Empirical

"local ties" between these pairs of stations were derived from the same

cumulative solution as in 1) and used to introduce the 3 new stations in

IGb08. All 3 new stations successfully passed the validation test

described in 1).

3) Application of position offsets to account for metadata corrections

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As explained in IGSMAIL-6662, sub-type calibrations will come into use on

week 1709 for the JPSREGANT_DD_E and JPSREGANT_SD_E antennas and replace

the type mean calibrations used so far. To make IGb08 consistent with the

new sub-type calibrations, position offsets were derived from differential

PPP tests and applied to the IGS08 positions of the 5 affected IGS08

stations (CAGZ, CONZ, KHAJ, MDVJ, ZIMJ).

It was recently discovered that a wrong antenna type had been reported in

the sitelogs of 2 IGS08 stations (ALRT, NAIN). To make IGb08 consistent

with the right antenna type (now in use), position offsets were derived

from differential PPP tests and applied to the IGS08 positions ALRT and

NAIN.

4) Discontinuity suppressions

-----------------------------

The discontinuities introduced for ALRT and NAIN at the time when their

sitelogs were corrected will be removed with the switch to IGb08.

Two discontinuities were introduced when the radome of CRO1 was removed

and re-installed in 2011. But no significant jump is in fact detectable in

CRO1's coordinate time series. Both discontinuities will thus be removed

with the switch to IGb08 and CRO1 will become usable again as a Reference

Frame station.

5) Station suppression

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Due to uncertainty about its radome loss (IGSSTATION-4610), BRMU (Bermuda)

was removed from IGb08 for the period after 2003.