WHY DOES THE IGS CARE ABOUT EOPs?

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WHY DOES THE IGS CARE ABOUT EOPs?

• Summary of core products of the International
  GNSS
• Service (IGS)
• Ultra-Rapid (real-time), Rapid, Final series
• outputs orbits, polar motion/LOD, clocks,
  station positions
• Ultra-Rapid products very widely used for many
• demanding real-time applications
• e.g., very rapid tropo water vapor soundings for
  meteo models
• natural hazards monitoring
• Ultra-Rapid product quality depends on EOP
• prediction accuracy
• latest observed orbits projected into future
  with EOP predictions
• EOP prediction errors limit accuracy of IGS
  real-time orbits

Jim Ray IGS Analysis Center Coordinator NOAA/Natio
nal Geodetic Survey
NGA Future EOP Prediction Workshop, Springfield,
VA, 17 November 2011
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IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011) IGS Core Product Series (2011)
Series Series Series ID ID Latency Latency Issue times (UTC) Issue times (UTC) Issue times (UTC) Data spans (UTC) Data spans (UTC) Data spans (UTC) Remarks Remarks Remarks Remarks
Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) IGU IGU real-time real-time _at_ 0300, 0900, 1500, 2100 _at_ 0300, 0900, 1500, 2100 _at_ 0300, 0900, 1500, 2100 24 hr _at_ 0000, 0600, 1200, 1800 24 hr _at_ 0000, 0600, 1200, 1800 24 hr _at_ 0000, 0600, 1200, 1800 ? for real-time apps ? GPS GLONASS ? issued with prior IGA ? for real-time apps ? GPS GLONASS ? issued with prior IGA ? for real-time apps ? GPS GLONASS ? issued with prior IGA ? for real-time apps ? GPS GLONASS ? issued with prior IGA

Ultra-Rapid (observed half) Ultra-Rapid (observed half) Ultra-Rapid (observed half) IGA IGA 3 - 9 hr 3 - 9 hr _at_ 0300, 0900, 1500, 2100 _at_ 0300, 0900, 1500, 2100 _at_ 0300, 0900, 1500, 2100 -24 hr _at_ 0000, 0600, 1200, 1800 -24 hr _at_ 0000, 0600, 1200, 1800 -24 hr _at_ 0000, 0600, 1200, 1800 ? for near real-time apps ? GPS GLONASS ? issued with following IGU ? for near real-time apps ? GPS GLONASS ? issued with following IGU ? for near real-time apps ? GPS GLONASS ? issued with following IGU ? for near real-time apps ? GPS GLONASS ? issued with following IGU

Rapid Rapid Rapid IGR IGR 17 - 41 hr 17 - 41 hr _at_ 1700 daily _at_ 1700 daily _at_ 1700 daily 12 hr _at_ 1200 12 hr _at_ 1200 12 hr _at_ 1200 ? for near-definitive, rapid apps ? GPS only ? for near-definitive, rapid apps ? GPS only ? for near-definitive, rapid apps ? GPS only ? for near-definitive, rapid apps ? GPS only

Final Final Final IGS IGS 11 - 17 d 11 - 17 d weekly each Thursday weekly each Thursday weekly each Thursday 12 hr _at_ 1200 for 7 d 12 hr _at_ 1200 for 7 d 12 hr _at_ 1200 for 7 d ? for definitive apps ? GPS GLONASS ? for definitive apps ? GPS GLONASS ? for definitive apps ? GPS GLONASS ? for definitive apps ? GPS GLONASS

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IGS Ultra-Rapid Update Cycle IGS Ultra-Rapid Update Cycle IGS Ultra-Rapid Update Cycle IGS Ultra-Rapid Update Cycle IGS Ultra-Rapid Update Cycle IGS Ultra-Rapid Update Cycle IGS Ultra-Rapid Update Cycle IGS Ultra-Rapid Update Cycle IGS Ultra-Rapid Update Cycle IGS Ultra-Rapid Update Cycle
day 1 day 1 day 1 day 1 day 2 day 2 day 2 day 2 day 3 day 3
? ? ? ? ? ? ? ?

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00h 06h 12h 18h 00h 06h 12h 18h 00h 06h

24 hr of observations 24 hr of observations 24 hr of observations ? ? observed EOPs observed EOPs
24 hr of predictions 24 hr of predictions 24 hr of predictions ? ? predicted EOPs predicted EOPs

IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval IGU updates every 6 hr are always 3 hr after the beginning of each prediction interval

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IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011) IGS Core Product Accuracies (2011)
Series Series Series ID Product Types Product Types Product Types Product Types Product Types Accuracies Accuracies Accuracies Accuracies Output Intervals Output Intervals Output Intervals
Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) IGU ? GPS orbits ? GPS orbits ? GPS orbits ? GPS orbits ? GPS orbits 5 cm (1D) 5 cm (1D) 5 cm (1D) 5 cm (1D) 15 min 15 min 15 min
Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) IGU ? GLONASS orbits ? GLONASS orbits ? GLONASS orbits ? GLONASS orbits ? GLONASS orbits 10 cm (1D) 10 cm (1D) 10 cm (1D) 10 cm (1D) 15 min 15 min 15 min
Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) IGU ? GPS SV clocks ? GPS SV clocks ? GPS SV clocks ? GPS SV clocks ? GPS SV clocks 3 ns RMS / 1.5 ns Sdev 3 ns RMS / 1.5 ns Sdev 3 ns RMS / 1.5 ns Sdev 3 ns RMS / 1.5 ns Sdev 15 min 15 min 15 min
Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) Ultra-Rapid (predicted half) IGU ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD 250 µas / 50 µs 250 µas / 50 µs 250 µas / 50 µs 250 µas / 50 µs 6 hr 6 hr 6 hr

Ultra-Rapid (observed half) Ultra-Rapid (observed half) Ultra-Rapid (observed half) IGA ? GPS orbits ? GPS orbits ? GPS orbits ? GPS orbits ? GPS orbits 3 cm (1D) 3 cm (1D) 3 cm (1D) 3 cm (1D) 15 min 15 min 15 min
Ultra-Rapid (observed half) Ultra-Rapid (observed half) Ultra-Rapid (observed half) IGA ? GLONASS orbits ? GLONASS orbits ? GLONASS orbits ? GLONASS orbits ? GLONASS orbits 5 cm (1D) 5 cm (1D) 5 cm (1D) 5 cm (1D) 15 min 15 min 15 min
Ultra-Rapid (observed half) Ultra-Rapid (observed half) Ultra-Rapid (observed half) IGA ? GPS SV clocks ? GPS SV clocks ? GPS SV clocks ? GPS SV clocks ? GPS SV clocks 150 ps RMS / 50 ps Sdev 150 ps RMS / 50 ps Sdev 150 ps RMS / 50 ps Sdev 150 ps RMS / 50 ps Sdev 15 min 15 min 15 min
Ultra-Rapid (observed half) Ultra-Rapid (observed half) Ultra-Rapid (observed half) IGA ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD lt50 µas / 10 µs lt50 µas / 10 µs lt50 µas / 10 µs lt50 µas / 10 µs 6 hr 6 hr 6 hr

Rapid Rapid Rapid IGR ? GPS orbits ? GPS orbits ? GPS orbits ? GPS orbits ? GPS orbits 2.5 cm (1D) 2.5 cm (1D) 2.5 cm (1D) 2.5 cm (1D) 15 min 15 min 15 min
Rapid Rapid Rapid IGR ? GPS SV station clocks ? GPS SV station clocks ? GPS SV station clocks ? GPS SV station clocks ? GPS SV station clocks 75 ps RMS / 25 ps Sdev 75 ps RMS / 25 ps Sdev 75 ps RMS / 25 ps Sdev 75 ps RMS / 25 ps Sdev 5 min 5 min 5 min
Rapid Rapid Rapid IGR ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD lt40 µas / 10 µs lt40 µas / 10 µs lt40 µas / 10 µs lt40 µas / 10 µs daily daily daily

Final Final Final IGS ? GPS orbits ? GPS orbits ? GPS orbits ? GPS orbits ? GPS orbits lt2.5 cm (1D) lt2.5 cm (1D) lt2.5 cm (1D) lt2.5 cm (1D) 15 min 15 min 15 min
Final Final Final IGS ? GLONASS orbits ? GLONASS orbits ? GLONASS orbits ? GLONASS orbits ? GLONASS orbits lt5 cm (1D) lt5 cm (1D) lt5 cm (1D) lt5 cm (1D) 15 min 15 min 15 min
Final Final Final IGS ? GPS SV station clocks ? GPS SV station clocks ? GPS SV station clocks ? GPS SV station clocks ? GPS SV station clocks 75 ps RMS / 20 ps SDev 75 ps RMS / 20 ps SDev 75 ps RMS / 20 ps SDev 75 ps RMS / 20 ps SDev 30 s (SVs) 5 min 30 s (SVs) 5 min 30 s (SVs) 5 min
Final Final Final IGS ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD ? EOPs PM LOD lt30 µas / 10 µs lt30 µas / 10 µs lt30 µas / 10 µs lt30 µas / 10 µs daily daily daily
Final Final Final IGS ? Terrestrial frames ? Terrestrial frames ? Terrestrial frames ? Terrestrial frames ? Terrestrial frames 2 mm NE / 5 mm U 2 mm NE / 5 mm U 2 mm NE / 5 mm U 2 mm NE / 5 mm U weekly weekly weekly

• IGS aims for 1 cm orbit 1 mm terrestrial
  accuracies
• to satisfy most demanding mm-level user
  application requirements

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Rotational Transform Observed EOPs(t)
Observed orbit Crust-fixed frame
Observed orbit Inertial frame
1)
Projected orbit Inertial frame
Observed orbit Inertial frame
2)
Rotational Transform Observed Predicted
EOPs(t)
Observed Projected orbit Crust-fixed frame
3)

• Errors in obs EOPs cancel out in
  forward/reverse transforms
• but EOP prediction errors fully embedded in
  crust-fixed orbit predictions
• typical prediction errors 0.4 mas/d for PM
  0.1 ms/d 1.5 mas/d for UT1
• 0.1 ms 1.5 mas 4.6 cm _at_ Earth 19.4 cm
  _at_ GPS

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Ultra-Rapid AC Orbit Comparisons (over 48 hr)

• Performance among Analysis Centers has become
  bimodal
• SIO USNO have been excluded for gt2 year
• AC quality is more uniform over first 6 hr of
  orbit predictions
• biggest differences occur for 6 24 hr orbit
  predictions

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Some IGU AC Orbits Have Large Rotations
0.5 mas 64 mm error _at_ GPS hgt

• SIO USNO have large Z rotational errors also Y
• CODE sometimes also has moderately large Z
  rotations
• these AC rotations probably from poor orbit
  modeling, not EOP predictions

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Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009)
DX DY DZ RX RY RZ SCL RMS WRMS MEDI TOTAL ERR
IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions
mean 3.5 -0.6 0.3 0.3 0.8 3.1 -0.7 28.9 21.3 15.6 41.7
std dev 4.7 4.9 3.4 13.8 16.3 27.2 2.6 19.7 8.0 2.6

IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions
mean 1.1 0.3 -0.1 -0.5 -0.6 -0.9 -1.3 64.7 47.3 30.2 80.2
std dev 1.8 2.0 3.8 21.9 31.2 52.0 1.9 33.3 16.3 6.0

IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations
mean 1.2 0.3 0.1 -0.2 0.9 2.6 -1.2 9.0 8.0 7.2 16.3
std dev 0.8 0.9 1.3 3.4 3.4 12.7 1.5 1.6 1.3 1.2

• Orbit errors double when prediction interval
  increases by x4
• IGA total err only 40 worse than IGRs (but 175
  worse for RZ)

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Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009)
DX DY DZ RX RY RZ SCL RMS WRMS MEDI TOTAL ERR
IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions
mean 3.5 -0.6 0.3 0.3 0.8 3.1 -0.7 28.9 21.3 15.6 41.7
std dev 4.7 4.9 3.4 13.8 16.3 27.2 2.6 19.7 8.0 2.6

IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions
mean 1.1 0.3 -0.1 -0.5 -0.6 -0.9 -1.3 64.7 47.3 30.2 80.2
std dev 1.8 2.0 3.8 21.9 31.2 52.0 1.9 33.3 16.3 6.0

IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations
mean 1.2 0.3 0.1 -0.2 0.9 2.6 -1.2 9.0 8.0 7.2 16.3
std dev 0.8 0.9 1.3 3.4 3.4 12.7 1.5 1.6 1.3 1.2

Z rotation errors are largest RT error from
UT1 prediction errors

• Largest RT orbit prediction error comes from UT1
  predictions
• IGA accuracy also limited by RZ rotations

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Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009) Ultra-Rapid Orbit Diffs (mm) wrt IGR (2009)
DX DY DZ RX RY RZ SCL RMS WRMS MEDI TOTAL ERR
IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions IGU 6-hr predictions
mean 3.5 -0.6 0.3 0.3 0.8 3.1 -0.7 28.9 21.3 15.6 41.7
std dev 4.7 4.9 3.4 13.8 16.3 27.2 2.6 19.7 8.0 2.6

IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions IGU 24-hr predictions
mean 1.1 0.3 -0.1 -0.5 -0.6 -0.9 -1.3 64.7 47.3 30.2 80.2
std dev 1.8 2.0 3.8 21.9 31.2 52.0 1.9 33.3 16.3 6.0

IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations IGA observations
mean 1.2 0.3 0.1 -0.2 0.9 2.6 -1.2 9.0 8.0 7.2 16.3
std dev 0.8 0.9 1.3 3.4 3.4 12.7 1.5 1.6 1.3 1.2

due to modelling of orbit dynamics
large X, Y rotation errors from PM prediction
errors

• Next largest RT limits from orbit modelling
  (solar radiation pressure effects) PM
  prediction errors

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EOP Error Sources

• Station-related measurements
• thermal noise
• instrumentation
• propagation delays
• multipath, etc
• sStation 1/vNStation

• Geophysical parameter models
• esp near S1,
• K1, K2 tidal
• periods
• AAM/OAM
• errors

• Source-related errors
• orbit dynamics
• (GPS, SLR, DORIS)
• quasar structures
• (VLBI)
• sSource 1/vNSource

sEOP

• Possible improvements

• new subdaily EOP
• tide model ?
• better handling of
• parameter
• constraints ?
• modern theory of
• Earth rotation ?

• more robust SLR,
• VLBI networks ?
• more stable site
• installations ?
• near asymptotic limit
• for GPS already

• new GNSS
• constellations
• better GNSS orbit
• models ?
• quasar structure
• models (VLBI) ?

? Multi-technique EOP combinations mostly
sub-optimal ! ?
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Conclusions

• Generally, IGA/IGU near- real-time orbits
  EOPs are of very high quality
• could use more better input Analysis Center
  solutions
• Rotations are leading real-time orbit error
• due to UT1 PM prediction errors used for IGU
  orbits
• models for orbit dynamics also add some
  rotational errors for some ACs
• EOP services could better use IGU products
• provide updates at least 4 times daily
• seek better input AAM OAM predictions
• improve combination algorithms
• present IERS predictions generally not adequate
  for IGS requirements
• IGS ACs generate better 1-day PM predictions
  internally from their own latest measurements
  we cannot do that for UT1 though
• Better model for subdaily tidal EOP variations
  also needed
• errors of IERS model alias into GPS orbit
  parameters