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IGS Contribution to ITRF

IGS Contribution to ITRF. Zuheir Altamimi & Xavier Collilieux IGN, France. Outline. IGS/GPS contribution to ITRF Some lessons from ITRF2005 IGS network and loading effects Polar motion Constraints Network effect Origin and Scale from GPS ? Repeatability – Internal precision

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IGS Contribution to ITRF

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  1. IGS Contribution to ITRF Zuheir Altamimi & Xavier Collilieux IGN, France

  2. Outline • IGS/GPS contribution to ITRF • Some lessons from ITRF2005 • IGS network and loading effects • Polar motion • Constraints • Network effect • Origin and Scale from GPS ? • Repeatability – Internal precision • Conclusion

  3. GPS Contribution to the ITRF • Strengths • Enforces the link between SLR and VLBI • Precise polar motion • Acces to ITRF and its densification via IGS products • Geographic density: Improve plate motion estimate & NNR condition implementation • Weaknesses • Discontinuities due to equipement changes • Antenna PCVs • Imprecise TRF origin and scale ? Something to improve here ?

  4. Current ITRF Derivation Step 1 S1 S2 S3 … Sn VLBI TRF (X, V)+ EOP (SINEX) W1 W2 … Wn SLR TRF (X, V)+ EOP (SINEX) Stacking W1 W2 … Wn GPS TRF (X, V)+ EOP (SINEX) W1 W2 … Wn DORIS TRF (X, V)+ EOP (SINEX) Combination ITRF Local Ties Step 2 TRF (X, V)+ EOP (SINEX)

  5. ITRF2005: Distribution and number of the IGS stations X Percentage of stations Y Z Number of stations

  6. ITRF2005:IGS weekly WRMS

  7. Loading effects on IGS network WRMS – 2D WRMS - UP Synthetic data Loading

  8. Loading effects on IGS network WRMS - UP WRMS – 2D Synthetic data Loading Loading+Flicker Noise According to Williams et al., 2004 variance values, rescaled by 60%

  9. Loading effects on IGS network WRMS - UP WRMS – 2D Synthetic data Loading Loading+Flicker Noise Loading+Flicker Noise+Mes. Noise

  10. Loading effects on IGS network Synthetic data Real data Loading IGS combined Loading+Flicker Noise Loading+Flicker Noise+Mes. Noise

  11. Network effect evaluated using a loading model (Tonie van Dam)Comparison with IVS and ILRS network East North Up VLBI SLR GPS

  12. IGS weekly WRMS Week 1400

  13. Week 1400 effect Week 1400

  14. EOP constraints ? Ex from DORIS Polar motion differences wrt IGS DORIS IGN Free solution DORIS LCA EOP Continuity conditions added

  15. Network effect on EOPsChange the RF Core sites by 10 sites Main difference Drift: Xp: 2 µas/yr Yp: 1 µas/yr

  16. TRF Origin & Scale from GPS ?

  17. IGS Reprocessed solutions : Origin & Scale

  18. Some Origin & Scale after W1400

  19. Impact of Orbit Parameters on TRF 4 weeks from ESOC: Default: 18 orbit parameters fixed Free: 9 CODE RPRs are free

  20. GPS PDR Origin & Scale wrt ITRF2005

  21. Repeatability – Internal Precision

  22. IGS Reprocessing: Repeatability – Internal Precision ESA GFZ MIT PDR

  23. IGS Reprocessing: Repeatability – Internal PrecisionCombined solutions

  24. PDR vs IGS weekly WRMS IGS PDR

  25. Conclusions • Loading effects • GPS/IGS contains some noise, esp. at early dates • GPS/IGS network effect: ~1 mm /yr in the Up component • EOPs • Avoid continuity constraints • Network effect on the long-term: 2µas/yr • Repeatability (weekly): 2 & 4-5 mm Horizontal & Up • Origin and Scale from GPS ? • Origin: Agreement betwenn ACs 5mm in X & Y and 10 mm in Z • Origin: Orbit parameters impact the Z component • Scale: after W1400 & from reprocessing AC agreement at 0.5 ppb • Next ITRF: GPS Reprocessing is absolutely needed

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