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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
GPS- and VLBI-derived Subdaily Estimates of Earth's Rotation and Their Impact on Global Solutions
Peter Steigenberger, Urs HugentoblerTechnische Universität München
Thomas Artz, Sarah BöckmannInstitut für Geodäsie und Geoinformation, Universität Bonn
Simon Lutz, Rolf Dach Astronomisches Institut, Universität Bern
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Introduction
• Subdaily variations of Earth’s rotation are usually accounted for with the model recommended by the IERS Conventions 2003
• Studies of subdaily Earth rotation variations with GPS and VLBI have been carried out since more than a decade
• Study the impact of introducing GPS- and VLBI-derived subdaily ERP models in global solutions
Outline
• Estimation and comparison of subdaily ERP models from GPS and VLBI time series
• Impact of sideband constraints and a priori models
• Impact of different a priori subdaily ERP models on global GPS and VLBI solutions
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Subdaily GPS and VLBI Solutions
VLBI• CALC/SOLVE• nutation fixed to IVS quarterly solution IVS09q2e
GPS• Bernese GPS Software• 3-day orbital arcs• diurnal retrograde polar motion blocked
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Subdaily GPS and VLBI Solutions: CONT05
September 2005
GPSCOD09
VLBIIGG09
IERS2003
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Formal Errors X-Pole
VBLIσ=0.37 mas
GPSσ=30 μas
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
• Estimation of 57 polar motion and 41 UT1 ocean tidal amplitudes in a weighted least squares adjustment
• Pseudo-observations: - GPS: polar motion rates, length of day- VLBI: polar motion, UT1
• Constraints for sidebands that cannot be solved for
Estimation of Subdaily ERP Models
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Major Tidal ConstituentsDiurnal prograde Semi-diurnal prograde
Semi-diurnal Diurnal
Semi-diurnal retrograde
PolarMotion
UT1TUM08COD09IGG09
TUM08CIERS2003
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Small Tidal Constituents: Retrograde Polar Motion
IERS2003
TUM08 COD09
IGG09
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Differences of COD09 w.r.t. IERS2003
PolarMotion
UT1
Diurnal progradeSemi-diurnal prograde
Semi-diurnal Diurnal
Semi-diurnal retrograde
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Comparison of All Estimated Tidal ConstituentsMean RMS differences of estimated amplitudes
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Sideband Constraints
A time series of at least 18.6 years is needed to properly solve for the sidebands of the tidal constituents
Constraints for the sideband amplitudes:
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Impact of Sideband Constraints
diurnal prograde semidiurnal prograde semidiurnal retrograde
Polar motion differences of GPS and VLBI models with and without sideband constraints
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Impact of a Priori Models
Differences of VLBI models
with IERS2003 and GSFC hf1102a a priori model
diurnal UT semidiurnal UT
diurnal prograde PM semidiurnal prograde PM semidiurnal retrograde PM
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Impact on Global Solutions
Aliasing effects:• 24 hours batches (GPS and VLBI)• Orbit repeat period (GPS)
GPS: Jan 2000 – Dec 2008
IERS2003 Reference solutionTUM08 GPS, 2hCOD09 GPS, 1hIGG09 VLBI, 1hTUM08C GPS/VLBI, 2h/1h
Global GPS and VLBI solutions with different subdaily a priori ERP models
VLBI: Mar 1984 – Dec 2008
IERS2003 Reference solutionIGG09 VLBI, 1hhf1102a GSFC model for
CALC/SOLVE
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Aliasing Effects
24h processing batches Orbit repeat period
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
GPS Earth Rotation Parameters: IERS2003/COD09 (1)
Estimated parameters per daily solution:• Offset and rate for polar motion• Rate for UT1 (=-LOD)
ERP difference time series of the GPS solutions IERS2003 and COD09
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
GPS Earth Rotation Parameters: IERS2003/COD09 (2)
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Spectra ERP Differences: IERS2003/COD09
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Spectra ERP Differences: IERS2003/COD09
Aliasing effects between 24 hours and …
M2 14.8 d L2 31.9 d
μ2 7.4 d
L2 31.9 d
M2 14.8 d
μ2 7.4 d
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Spectra ERP Differences: IERS2003/COD09
OO1 13.2 d
J1 25.6 d
O1 14.2 d
Aliasing effects between 24 hours and …
M2 14.8 dQ1 9.4 d
O1 14.2 d
M2 14.8 dQ1 9.4 d
O1 14.2 d
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
VLBI Earth Rotation Parameters: IERS2003/IGG09
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
GPS Station Coordinates: IERS2003/COD09BOR1, Borowiec, Poland
STDN 0.08 mm
STDE 0.08 mm
STDU 0.10 mm
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Spectra Coordinates Differences: IERS2003/COD09P
ower
Period [d] Period [d]Period [d]
BOR1, Borowiec, Poland
ΔNorth ΔUpΔEast
14.8 d
13.6 d
14.8 d
118 d
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GPS Geocenter: IERS2003/COD09
STDX 0.26 mm
STDY 0.28 mm
STDZ 0.73 mm
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Orbit Residuals: IERS2003/COD09
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IERS Workshop on EOP Combination and Prediction, Warsaw, 19-21 October 2009
Conclusions• GPS- and VLBI-derived subdaily ERP estimates agree on the
5 μas level for polar motion and 0.3 μs level for UT1• Impact of different subdaily ERP models on global solutions visible in
different parameter types:
• Earth rotation parameters: - ± 15 μas for polar motion- ± 100 μas/d for polar motion rates- ± 10 μs/d for LOD
• Coordinate time series: few 1/10 mm level
• Geocenter: below 1 mm for X and Y, up to 2 mm for Z
• Satellite orbits: up to 2 cm
• Several aliasing periods clearly visible, more pronounced for GPS compared to VLBI