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The IGS contribution to ITRF2014 Paul Rebischung, Bruno Garayt, Zuheir Altamimi, Xavier Collilieux 26 th IUGG General Assembly, Prague, 28 June 2015. Outline. Daily IGS repro2 SINEX combinations Combined IGS repro2 dataset Origin/scale of daily combined solutions

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Outline

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  1. The IGS contribution to ITRF2014Paul Rebischung, Bruno Garayt, Zuheir Altamimi, Xavier Collilieux26th 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 Smootheddaily 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: ≈ 30-40 μas (pole coordinates),≈ 150-200 μas/d (pole rates), ≈ 15-30 μs/d (LOD)

  4. 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 ofthe 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 coordinatesderivedfrom the SLR contribution to ITRF2014(All time seriesshown in the figure are detrended.) Smoothedperiodograms of the:― repro2 ― SLR-derivedgeocenter time seriesshown in the left figures. Spectral power in mm2.

  6. Geocenter motion (2/2) • 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 Results from trend + annual + semi-annual fits to: ― the repro2 combined geocenter time series ― geocenter time seriesderivedfrom the SLR contribution to ITRF2014

  7. Terrestrial scale • 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? ― Scalefactorsestimatedbetween the daily repro2combined solutions and IGb08 ― Scalefactorsderivedfrom a loading model (ECMWF+GLDAS+ECCO2; http://loading.u-strasbg.fr) Smoothedperiodograms [mm2] of the:― repro2 ― loading model-derivedscale factor time seriesshown in the left figure. Results from trend+annual+semi-annual fits to the: ― repro2 ― loading model-derivedscale factor time seriesshown in the left figure.

  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) andnumbers 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 stackingresiduals (East, North, Up) Provisional ITRF2014 GNSS network

  13. Stacked periodograms • White + flickernoise background • GPS draconiticharmonics upto the 8th • Fortnightly tidallines: • Mf tide (13.6 d) • O1 alias (14.2 d) • M2 alias (14.8 d) StackedLomb-Scarglenormalizedperiodograms ofthe stackingresidual time series ― East (withannual + semi-annualtermsestimated) ―North/10 (withannual + semi-annualtermsestimated) ―Up/100 (withannual + semi-annualtermsestimated)

  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. Thankyou for your attention!

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