igs contribution to itrf
DESCRIPTION
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 PresentationTRANSCRIPT
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Workshop, Miami, June 2008
IGS Contribution to ITRF
Zuheir Altamimi & Xavier CollilieuxIGN, France
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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
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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 ?
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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…
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Workshop, Miami, June 2008
ITRF2005: Distribution and number of the IGS stations
Percentage of stations
X
Y
Z
Number of stations
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Workshop, Miami, June 2008
ITRF2005:IGS weekly WRMS
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Loading
Synthetic data
Loading effects on IGS network
WRMS - UP WRMS – 2D
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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
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Workshop, Miami, June 2008
Loading
Loading+Flicker Noise
Loading+Flicker Noise+Mes. Noise
Synthetic data
Loading effects on IGS network
WRMS - UP WRMS – 2D
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Workshop, Miami, June 2008
Loading
Loading+Flicker Noise
Loading+Flicker Noise+Mes. Noise
IGS combined
Synthetic data Real data
Loading effects on IGS network
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Network effect evaluated using a loading model (Tonie van Dam)Comparison with IVS and ILRS network
VLBI
SLR
GPS
East North Up
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Workshop, Miami, June 2008
IGS weekly WRMS Week 1400
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Week 1400 effect Week 1400
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Workshop, Miami, June 2008
EOP constraints ? Ex from DORIS
DORIS IGNFree solution
DORIS LCAEOP Continuity conditions added
Polar motion differences wrt IGS
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Network effect on EOPsChange the RF Core sites by 10 sites
Main differenceDrift:Xp: 2 µas/yrYp: 1 µas/yr
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Workshop, Miami, June 2008
TRF Origin & Scale from GPS ?
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IGS Reprocessed solutions : Origin & Scale
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Some Origin & Scale after W1400
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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
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Workshop, Miami, June 2008
GPS PDR Origin & Scale wrt ITRF2005
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Repeatability – Internal Precision
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IGS Reprocessing: Repeatability – Internal Precision
ESA GFZ
MIT PDR
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IGS Reprocessing: Repeatability – Internal PrecisionCombined solutions
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PDR vs IGS weekly WRMS
PDRIGS
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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