IGb08______IGS08更新

http://igscb.jpl.nasa.gov/pipermail/igsmail/2012/006655.html

Dear IGS colleagues,Either because they are decommissioned, dormant or have been affected bydiscontinuities since 2009.5, a large number of IGS08 stations are nowunusable for operational reference frame alignments. In particular, theIGS08 core network has dropped to about 50 usable stations recently,leaving large holes in South America, Africa, and Eastern Asia. Thissituation led us to propose an update of IGS08, called IGb08.IGb08 mainly includes new sets of coordinates for 33 IGS08 stations havingbeen affected by position discontinuities since 2009.5, and 3 new stationsco-located with decommissioned IGS08 stations. (The various changes fromIGS08 to IGb08 are described in more details below.) All in all, thisupdate will increase the number of usable Reference Frame stations byabout 36 and the number of usable core stations by about 15.IGb08.snx is available with some ancillary files atftp://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 1701IGb08 will officially replace IGS08 starting with products of GPS week1709 (7 October 2012). This switch aims at stabilizing the reference framealignment of the IGS products and should not lead to any particularinconvenience for users.Paul Rebischung, on behalf of the IGS Reference Frame Working Group1) Introduction of post-discontinuity coordinates-------------------------------------------------38 IGS08 stations with discontinuities since 2009.5 were first identifiedas "repairable". A special cumulative solution was then formed, based onthe igb/igs weekly solutions up to week 1701, in which station annualmotions were estimated together with their positions and velocities.Empirical offsets from the pre-break to the post-break station positionswere derived from this cumulative solution and used to introducepost-break coordinates for the 38 stations in IGb08.As a validation, IGb08 was used to align the igs weekly solutions of weeks1632-1701. A check of the alignment residuals for the 38 newly introducedpoints 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-----------------------------------------------------------------------3 pairs of decommissioned IGS08 stations co-located with currently activestations were identified (CHAT/CHTI, MALI/MAL2, NOUM/NRMD). Empirical"local ties" between these pairs of stations were derived from the samecumulative solution as in 1) and used to introduce the 3 new stations inIGb08. All 3 new stations successfully passed the validation testdescribed in 1).3) Application of position offsets to account for metadata corrections----------------------------------------------------------------------As explained in IGSMAIL-6662, sub-type calibrations will come into use onweek 1709 for the JPSREGANT_DD_E and JPSREGANT_SD_E antennas and replacethe type mean calibrations used so far. To make IGb08 consistent with thenew sub-type calibrations, position offsets were derived from differentialPPP tests and applied to the IGS08 positions of the 5 affected IGS08stations (CAGZ, CONZ, KHAJ, MDVJ, ZIMJ).It was recently discovered that a wrong antenna type had been reported inthe sitelogs of 2 IGS08 stations (ALRT, NAIN). To make IGb08 consistentwith the right antenna type (now in use), position offsets were derivedfrom differential PPP tests and applied to the IGS08 positions ALRT andNAIN.4) Discontinuity suppressions-----------------------------The discontinuities introduced for ALRT and NAIN at the time when theirsitelogs were corrected will be removed with the switch to IGb08.Two discontinuities were introduced when the radome of CRO1 was removedand re-installed in 2011. But no significant jump is in fact detectable inCRO1's coordinate time series. Both discontinuities will thus be removedwith the switch to IGb08 and CRO1 will become usable again as a ReferenceFrame station.5) Station suppression----------------------Due to uncertainty about its radome loss (IGSSTATION-4610), BRMU (Bermuda)was removed from IGb08 for the period after 2003.