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The IGS contribution to ITRF2014 Paul Rebischung, Bruno Garayt, Zuheir Altamimi, Xavier Collilieux 26th IUGG General Assembly, Prague, 28 June.

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Presentation on theme: "The IGS contribution to ITRF2014 Paul Rebischung, Bruno Garayt, Zuheir Altamimi, Xavier Collilieux 26th IUGG General Assembly, Prague, 28 June."— Presentation transcript:

1 The IGS contribution to ITRF2014 Paul Rebischung, Bruno Garayt, Zuheir Altamimi, Xavier Collilieux th IUGG General Assembly, Prague, 28 June 2015

2 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

3 Daily IGS repro2 SINEX combinations
Smoothed daily WRMS of the « AC – combined » station position residuals AC contributions to the repro2 campaign Overall inter-AC agreement: Station positions: ≈ 1.5 mm (horizontal), ≈ 4 mm (vertical) Geocenter: ≈ 2-5 mm (X, Y), ≈ 5-10 mm (Z) Terrestrial scale: Excellent (< 1 mm; < 0.1 mm/yr) EOPs: ≈ μas (pole coordinates), ≈ μas/d (pole rates), ≈ μs/d (LOD)

4 Combined IGS repro2 dataset
7714 daily SINEX files Daily station positions, geocenter coordinates and EOPs January 2, → 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

5 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.

6 Geocenter motion (2/2) Non-negligible offsets and rates wrt ITRF2008
Offset at [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 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

7 Terrestrial scale Repro2 scale factor time series:
― Scale factors estimated between the daily repro combined solutions and IGb08 ― Scale factors derived from a loading model (ECMWF+GLDAS+ECCO2; Smoothed periodograms [mm2] of the: ― repro2 ― loading model-derived scale factor time series shown in the left figure. 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?

8 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 2090 discontinuities detected (≈ 1.8 per station) ― antenna change ― receiver change ― earthquake ― 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

9 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

10 SAMO (Samoan Islands) log + δV δV log + δV

11 COCO (Cocos Islands) exp exp exp log exp log

12 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

13 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/ (with annual + semi-annual terms estimated)

14 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)

15 Thank you for your attention!


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