The IGS contribution to ITRF2014
Paul Rebischung, Bruno Garayt, Zuheir Altamimi, Xavier Collilieux
26th IUGG General Assembly, Prague, 28 June 2015
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Outline
• Daily IGS repro2 SINEX combinations
• Combined IGS repro2 dataset
– Origin/scale of daily combined solutions
• Modeling of station position time series
– Discontinuities
– Post-seismic deformations
• Long-term stacking (input to ITRF2014)
– Spectral analysis of residual time series
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Daily IGS repro2 SINEX combinations
AC contributions to the repro2 campaign
Smoothed daily WRMS of the « AC – combined »
station position residuals
• Overall inter-AC agreement:
–
–
–
–
Station positions:
Geocenter:
Terrestrial scale:
EOPs:
≈ 1.5 mm (horizontal), ≈ 4 mm (vertical)
≈ 2-5 mm (X, Y), ≈ 5-10 mm (Z)
Excellent (< 1 mm; < 0.1 mm/yr)
≈ 30-40 μas (pole coordinates),
≈ 150-200 μas/d (pole rates), ≈ 15-30 μs/d (LOD)
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Combined IGS repro2 dataset
• 7714 daily SINEX files
– Daily station positions, geocenter coordinates and EOPs
– January 2, 1994 → February 14, 2015
– 1848 stations
Stations included in the daily repro2 combined solutions.
The size and color of each dot is function of
the number of days n each station is present.
Histograms of the lengths (top)
and numbers of data points (bottom)
of the repro2 station position time series
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Geocenter motion (1/2)
(X)
(Y)
(Z)
― Daily repro2 combined geocenter coordinates
― Smoothed repro2 combined geocenter coordinates
― Smoothed geocenter coordinates derived from the
SLR contribution to ITRF2014
(All time series shown in the figure are detrended.)
Smoothed periodograms of the:
― repro2
― SLR-derived
geocenter time series shown in the left figures.
Spectral power in mm2.
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Geocenter motion (2/2)
Offset at
2005. [mm]
Rate
[mm/yr]
Annual amp
[mm]
Annual phi
[deg]
Semi-ann
amp [mm]
Semi-ann
phi [deg]
WRMS
[mm]
XGC
1.6
0.28
1.5 / 2.6
41 / 48
0.9 / 0.8
271 / 282
3.5 / 2.9
YGC
2.6
-0.40
3.6 / 2.8
310 / 320
0.2 / 0.3
336 / 159
3.5 / 2.9
ZGC
7.0
-0.18
3.8 / 5.9
181 / 26
1.3 / 1.4
223 / 202
6.4 / 5.2
Results from trend + annual + semi-annual fits to:
― the repro2 combined geocenter time series
― geocenter time series derived from the SLR contribution to ITRF2014
• Non-negligible offsets and rates wrt ITRF2008
• Annual geocenter motion:
– Under-estimated along X
– Over-estimated along Y
– Out-of-phase with SLR along Z
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Terrestrial scale
Smoothed periodograms [mm2] of the:
― repro2
― loading model-derived
scale factor time series shown in the left figure.
― Scale factors estimated between the daily repro2
combined solutions and IGb08
― Scale factors derived from a loading model
(ECMWF+GLDAS+ECCO2; http://loading.u-strasbg.fr)
Annual amp
[mm]
Annual phi
[deg]
Semi-ann
amp [mm]
Semi-ann
phi [deg]
WRMS
[mm]
1.4 / 0.8
-114 / -103
0.5 / 0.1
118 / 138
0.8 / 0.5
Results from trend+annual+semi-annual fits to the:
― repro2
― loading model-derived
scale factor time series shown in the left figure.
• Repro2 scale factor time series:
–
Mostly constituted of annual and semi-annual variations
–
Shows little evidence of draconitics
–
≈ Half can be explained by loading + network effect
→ Contribution of GNSS to the ITRF2014 temporal scale variations?
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Discontinuity detection
• Visual detection with help of:
– List of equipment changes
– Catalogue of co-seismic displacements (updated from Métivier et al., 2014)
• Analyzed 1176 stations with repro2 series > 700 days
― antenna change
– 2090 discontinuities detected
(≈ 1.8change
per station)
― receiver
― earthquake
Unknown:
425 (20%)
Equipment
changes:
1019 (49%)
Earthquakes:
646 (31%)
― 04:361:03530 – Sumatra Earthquake (9.0)
― 07:330:00000 – Antenna Change
― 12:102:31117 – Sumatra Earthquake (8.6)
Histograms of the lengths (top) and
numbers of data points (bottom)
of inter-discontinuity intervals
Distribution of
discontinuity causes
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Post-seismic deformation modeling
• Goal: correct post-seismic deformations before stacking
• For each E, N, H time series:
– Test following models: exp, log, exp+exp, exp+log [+ velocity disc.]
– Select best model based on Bayes’ Information Criterion (BIC)
• 209 models
• 139 stations
• 65 earthquakes
Stations with post-seismic models
Earthquake epicenters
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SAMO (Samoan Islands)
log + δV
δV
log + δV
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COCO (Cocos Islands)
exp
exp
exp
log
exp
log
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Long-term stacking (input to ITRF2014)
• Innovations:
– Post-seismic deformations corrected a priori
– Estimation of annual + semi-annual signals
• 1066 stations retained (yet)
– Time series > 700 days
– Well-behaved residuals
Daily WRMS of stacking residuals (East, North, Up)
Provisional ITRF2014 GNSS network
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Stacked periodograms
• White + flicker
noise background
• GPS draconitic
harmonics up
to the 8th
• Fortnightly tidal
lines:
– Mf tide (13.6 d)
– O1 alias (14.2 d)
– M2 alias (14.8 d)
Stacked Lomb-Scargle normalized periodograms of
the stacking residual time series
― East
(with annual + semi-annual terms estimated)
― North/10 (with annual + semi-annual terms estimated)
― Up/100 (with annual + semi-annual terms estimated)
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Next steps
• Prepare next IGS Reference Frame (IGS14/igs14.atx)
– Select subset of stable stations
– Re-estimate satellite antenna phase center offsets
– Take new ground antenna calibrations into account
• Prepare next-generation IGS cumulative solution
– Based on repro2 data + new discontinuity list
– How to deal with post-seismic deformations operationally?
• Scientific investigation:
– Analyze noise content in individual station position time series
– Study spatial structure of draconitic/fortnightly errors and of noise
– Study AC-specific errors (through AC-specific long-term stackings)
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Thank you for your attention!
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