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Current status of ITRF Co-location Sites

Current status of ITRF Co-location Sites. Zuheir Altamimi IGN-France ITRF Product Center. Co-locations. Co-location sites are vital for multi-technique combination (ITRF) Number & Distribution of co-location sites Quality of local ties

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Current status of ITRF Co-location Sites

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  1. Current status of ITRF Co-location Sites Zuheir Altamimi IGN-France ITRF Product Center

  2. Co-locations • Co-location sites are vital for multi-technique combination (ITRF) • Number & Distribution of co-location sites • Quality of local ties • They impact the combined frame parameters (Origin, Scale, Orientation)

  3. Current Co-locations (1999 on) (8) (59) (16) (2)

  4. (2) Missing Ties SLR/GPS DORIS/GPS (1) SAKAL Brewster Ottawa Krimea URUM MIZU KUNM Haleakala VLBI/SLR (1) VLBI/GPS (4)

  5. Missing Ties • There are missing ties for point(s) in sites having multiple points from one technique • Ties after EQ are not available, e.g. • Arequipa (SLR, GPS, DORIS) • Fairbanks (VLBI, GPS, DORIS) • Ties after EQ should be used with care, esp. in case of co-seismic effect !

  6. Dubious/Discrepant Ties Disagreement btw Terrestrial & Space Geodesy vectors • Hard to discriminate between the two • ~ 15 - 20 % of the total currently available ties are discrepant  1 cm (preliminary ITRF2004 analysis)

  7. Co-locationsA new difficulty • Most of IGS/GPS stations experience jumps (discontinuities) in the time series of station positions • Most of IGS/ILRS Co-location sites are concerned • A few SLR station discontinuities are detectable • Having only one tie: to which segment should the tie be applied ??? • Careful combination analysis is needed

  8. A Co-location site with Discontinuities X GPS SLR Tie Time

  9. Current VLBI-SLR Co-locations (1999 on) (9) Inhomogeneous distribution of VLBI&SLR Networks and their Co-locations ITRF Scale in danger !!!

  10. Current VLBI-GPS Co-locations (1999 on) (36)

  11. Current VLBI-DORIS Co-locations (1999 on) (9) Poor number and distribution of VLBI and DORIS Co-locations

  12. Current SLR-GPS Co-locations (1999 on) (25)

  13. Current SLR-DORIS Co-locations (1999 on) (7) Only 7 SLR-DORIS Co-locations

  14. Current DORIS-GPS Co-locations (1999 on) (37)

  15. Conclusions • Poor number&Distr. of SLR & VLBI Co-locations • Networks configuration needs improvemnt • GGOS WG on Networks, Communications & Infrastructure • To improve tie quality, ideally repeated surveys are needed (yearly, each 2 years) • Current Ties are available at: http://itrf.ensg.ign.fr/ITRF_solutions/2004/doc/ITRF2004-localties.tab

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