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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 - PowerPoint PPT Presentation
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Workshop, Miami, June 2008
IGS Contribution to ITRF
Zuheir Altamimi & Xavier CollilieuxIGN, France
Workshop, Miami, June 2008
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
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
TRF (X, V)+ EOP (SINEX)
TRF (X, V)+ EOP (SINEX)
TRF (X, V)+ EOP (SINEX)
TRF (X, V)+ EOP (SINEX)
Local Ties CombinationITRF
Stacking
S1 S2 S3 Sn…VLBI
SLR
GPS
DORIS
TRF (X, V)+ EOP (SINEX)
Step 1
Step 2
W1 W2 Wn…
W1 W2 Wn…
W1 W2 Wn…
Workshop, Miami, June 2008
ITRF2005: Distribution and number of the IGS stations
Percentage of stations
X
Y
Z
Number of stations
Workshop, Miami, June 2008
ITRF2005:IGS weekly WRMS
Workshop, Miami, June 2008
Loading
Synthetic data
Loading effects on IGS network
WRMS - UP WRMS – 2D
Workshop, Miami, June 2008
LoadingLoading+Flicker Noise
Synthetic data
According to Williams et al., 2004 variance values, rescaled by 60%
Loading effects on IGS network
WRMS - UP WRMS – 2D
Workshop, Miami, June 2008
Loading
Loading+Flicker Noise
Loading+Flicker Noise+Mes. Noise
Synthetic data
Loading effects on IGS network
WRMS - UP WRMS – 2D
Workshop, Miami, June 2008
Loading
Loading+Flicker Noise
Loading+Flicker Noise+Mes. Noise
IGS combined
Synthetic data Real data
Loading effects on IGS network
Workshop, Miami, June 2008
Network effect evaluated using a loading model (Tonie van Dam)Comparison with IVS and ILRS network
VLBI
SLR
GPS
East North Up
Workshop, Miami, June 2008
IGS weekly WRMS Week 1400
Workshop, Miami, June 2008
Week 1400 effect Week 1400
Workshop, Miami, June 2008
EOP constraints ? Ex from DORIS
DORIS IGNFree solution
DORIS LCAEOP Continuity conditions added
Polar motion differences wrt IGS
Workshop, Miami, June 2008
Network effect on EOPsChange the RF Core sites by 10 sites
Main differenceDrift:Xp: 2 µas/yrYp: 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 W1400
Workshop, Miami, June 2008
Impact of Orbit Parameters on TRF4 weeks from ESOC:Default: 18 orbit parameters fixedFree: 9 CODE RPRs are free
W1471 TX(mm) TY(mm) TZ(mm) Scale(ppb) Default -6.8 -0.3 -9.2 0.64 Free -7.0 0.2 4.1 0.54 W1472 Default -3.9 0.6 -5.2 0.41 Free -3.6 1.2 6.3 0.37 W1473 Default -6.9 0.6 -9.5 0.31 Free -7.7 1.8 6.0 0.27 W1474 Default -6.6 5.5 -9.3 0.43 Free -7.1 7.3 41.7 0.40
Workshop, Miami, June 2008
GPS PDR Origin & Scale wrt ITRF2005
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 PrecisionCombined solutions
Workshop, Miami, June 2008
PDR vs IGS weekly WRMS
PDRIGS
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 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