IGS Contribution to ITRF Zuheir Altamimi Xavier Collilieux
IGS Contribution to ITRF Zuheir Altamimi & Xavier Collilieux IGN, France Workshop, Miami, June 2008
Outline • • IGS/GPS contribution to ITRF Some lessons from ITRF 2005 IGS network and loading effects Polar motion – Constraints – Network effect • Origin and Scale from GPS ? • Repeatability – Internal precision • Conclusion Workshop, Miami, June 2008
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 ? Workshop, Miami, June 2008
Current ITRF Derivation Step 1 S 2 S 3 … Sn VLBI TRF (X, V)+ EOP (SINEX) SLR W 1 W 2 … GPS W 1 W 2 … DORISW 1 W 2 … Local Ties Wn Stacking Wn Wn TRF (X, V)+ EOP (SINEX) Combination ITRF (X, V)+ EOP (SINEX) Workshop, Miami, June 2008 Step 2
ITRF 2005: Distribution and number of the IGS stations X Percentage of stations Y Z Number of stations Workshop, Miami, June 2008
ITRF 2005: IGS weekly WRMS Workshop, Miami, June 2008
WRMS – 2 D Loading effects on IGS network WRMS - UP Synthetic data Loading Workshop, Miami, June 2008
WRMS – 2 D Loading effects on IGS network WRMS - UP Synthetic data Loading+Flicker Noise According to Williams et al. , 200 variance values, rescaled by 60% Workshop, Miami, June 2008
WRMS – 2 D Loading effects on IGS network WRMS - UP Synthetic data Loading+Flicker Noise +Mes. Noise Workshop, Miami, June 2008
IGS combined Real data Loading effects on IGS network Synthetic data Loading+Flicker Noise +Mes. Noise Workshop, Miami, June 2008
Network effect evaluated using a loading model (Tonie van Dam) Comparison with IVS and ILRS network East North Up VLBI SLR GPS Workshop, Miami, June 2008
IGS weekly WRMS Workshop, Miami, June 2008 Week 1400
Week 1400 effect Workshop, Miami, June 2008 Week 1400
EOP constraints ? Ex from DORIS Polar motion differences wrt IGS DORIS IGN Free solution DORIS LCA EOP Continuity conditions added Workshop, Miami, June 2008
Network effect on EOPs Change the RF Core sites by 10 sites Main difference Drift: Xp: 2 µas/yr Yp: 1 µas/yr Workshop, Miami, June 2008
TRF Origin & Scale from GPS ? Workshop, Miami, June 2008
IGS Reprocessed solutions : Origin & Scale Workshop, Miami, June 2008
Some Origin & Scale after W 1400 Workshop, Miami, June 2008
Impact of Orbit Parameters on TRF 4 weeks from ESOC: Default: 18 orbit parameters fixed Free: 9 CODE RPRs are free Workshop, Miami, June 2008
GPS PDR Origin & Scale wrt ITRF 2005 Workshop, Miami, June 2008
Repeatability – Internal Precision Workshop, Miami, June 2008
IGS Reprocessing: Repeatability – Internal Precision ESA GFZ MIT PDR Workshop, Miami, June 2008
IGS Reprocessing: Repeatability – Internal Precision Combined solutions Workshop, Miami, June 2008
PDR vs IGS weekly WRMS IGS PDR Workshop, Miami, June 2008
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: 2 µas/yr • Repeatability (weekly): 2 & 4 -5 mm Horizontal & Up • Origin and Scale from GPS ? – Origin: Agreement betwenn ACs 5 mm in X & Y and 10 mm in Z – Origin: Orbit parameters impact the Z component – Scale: after W 1400 & from reprocessing AC agreement at 0. 5 ppb • Next ITRF: GPS Reprocessing is absolutely needed Workshop, Miami, June 2008
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