1. AGU Fall meeting 2009 1 Quality assessment of GPS reprocessed Terrestrial Reference Frame 1 IGN/LAREG and GRGS 2 University of Luxembourg X Collilieux 1 Z Altamimi 1 L. Métivier 1 T. van Dam 2 Acknowledgment : J. Ray (NGS)

2. AGU Fall meeting 2009 2 Outline Data GPS Frame origin and scale. Investigation of their temporal behaviors Station position time series GPS TRF assessment Data Origin & Scale Station position time series TRF assessment

3. AGU Fall meeting 2009 3 Data ACEpochNb of stations IG1 combined1997.0-2009.5570 GFZ1998.0-2008.0248 ESA1997.0-2009.0358 COD1997.0-2009.0224 MIT1998.0-2008.0748 Nb of stations per week mi1 gf1 co1 es1 IGS Data Origin & Scale Station position time series TRF assessment

4. AGU Fall meeting 2009 4 GPS translation and scale (1/5) Comparison with ITRF2008 preliminary solution (SLR origin) mi1 Data Origin & Scale Station position time series TRF assessment

5. AGU Fall meeting 2009 5 GPS translation and scale (1/5) Comparison with ITRF2008 preliminary solution (SLR origin) mi1 gf1 Data Origin & Scale Station position time series TRF assessment

6. AGU Fall meeting 2009 6 GPS translation and scale (1/5) Comparison with ITRF2008 preliminary solution (SLR origin) mi1 gf1 co1 Data Origin & Scale Station position time series TRF assessment

7. AGU Fall meeting 2009 7 GPS translation and scale (1/5) Comparison with ITRF2008 preliminary solution (SLR origin) mi1 gf1 co1 es1 Data Origin & Scale Station position time series TRF assessment

8. AGU Fall meeting 2009 8 GPS translation and scale (2/5) Offset (t=2000) (mm) Drift (mm/yr) MinMaxMinMax TX -3.7 ± 0.2-0.2 ± 0.2-0.60 ± 0.05-0.12 ± 0.04 TY -5.4 ± 0.2-2.8 ± 0.2-0.06 ± 0.040.91 ± 0.06 TZ -13.5 ± 0.5-10.1 ± 0.40.34 ± 0.090.78 ± 0.13 Scale 8.5 ± 0.1 10.2 ± 0.1-0.38 ± 0.01-0.24 ± 0.01 W.r.t. ITRF2008 prel. GPS scale is based on ITRF2005 scale through GPS satellite antenna offsets. This non-zero scale offset is explained by: ITRF2008P and ITRF2005 scale difference Adoption of absolute phase center variations Data Origin & Scale Station position time series TRF assessment

9. AGU Fall meeting 2009 9 GPS translation and scale (3/5) Seasonal variations of the apparent geocenter motion mi1 gf1 co1 es1 SLR Good fit on Y component. Still inconsistent X and Z variations Data Origin & Scale Station position time series TRF assessment

10. AGU Fall meeting 2009 10 Loading model + + Loading effects 12 h 1 month 6 h Some examples GPS translation and scale (4/5) Loading model GPS data (ITRF2008) ~ Bad fit ~Good fit Comparison of scale variations with a loading model Data Origin & Scale Station position time series TRF assessment

11. AGU Fall meeting 2009 11 Station position time series – Scale issue As the scale behavior is stable : do not estimate scale non- linear temporal variations to avoid loosing loading signal Load mi1 gf1 co1 es1 Difference with the loading model mm Cause of these variations: Deficiency in the loading model Draconitic period (harmonics detected in the power spectra) Thermal effects Comparison of scale variations with a loading model Data Origin & Scale Station position time series TRF assessment

12. AGU Fall meeting 2009 12 Station position time series - Spectral map (1/2) Repeatability mi1 gf1 co1 es1 ITRF2008 ITRF2005 Data Origin & Scale Station position time series TRF assessment

13. AGU Fall meeting 2009 13 Station position time series - Spectral map (2/2) 5 latest years of IGS combined analysed for spectral content. Proportation of stations which detect a given frequency For the whole period, no difference between Acs, but the 6th harmonic more visible in the North Is the power of the 4th harmonic of the draconitic frequency lower in ITRF2008 data? Comparison of the amplitude of the 4th harmonic signal between: -ITRF2005 residuals (2001-2006) -ITRF2008 residuals (2004-2009) IG1 reprocessed IGS ITRF2005 Data Origin & Scale Station position time series TRF assessment

14. AGU Fall meeting 2009 14 Station position time series - Comparison with a loading model (2/3) Station considered GPS annual signal ampl. Loading model annual signal ampl. Period 1997.0-2006.0 ITRF2005 GPS (IGS) ITRF2008 GPS (IG1) Vertical Amplitude of the annual signal ρ = 43% ρ = 56% Data Origin & Scale Station position time series TRF assessment

15. AGU Fall meeting 2009 15 Comparison with a loading model (3/4) Horizontal Vertical ITRF2005 GPS (IGS) ITRF2008 GPS (IG1) Amplitude of the annual signal ρ = 43% ρ = 56% ρ = 17% ρ = 26% ρ = -13% ρ = -5% Data Origin & Scale Station position time series TRF assessment

16. AGU Fall meeting 2009 16 Comparison with a loading model (4/4) ITRF2005 GPS (IGS) ITRF2008 GPS (IG1) Phase of the annual signal : histogramme of the difference of phase between GPS and loading model Significant improvement in the height only Data Origin & Scale Station position time series TRF assessment

17. AGU Fall meeting 2009 17 Station position time series - Annual signal and AC solutions mi1 gf1 co1 es1 A. cos( ω. T–Φ) Φ Data Origin & Scale Station position time series TRF assessment

18. AGU Fall meeting 2009 18 Agreement with IVS VLBI reprocessed solution Made on GPS-VLBI co-location sites Height local tie residual improvement --------------------------------------------- WRMS Positions Velocities 2D h 2D h t=2000.0 mm mm/yr ------------------------------------------------------------------------ ITRF2005 0.3 1.6 0.1 0.5 ITRF2008P 0.1 0.8 0.1 0.4 ------------------------------------------------------------------------ Comparison with newly reprocessed VLBI (IVS) solution If VLBI positions and velocities are fixed to their estimated values, Data Origin & Scale Station position time series TRF assessment

19. AGU Fall meeting 2009 19 Conclusion Origin Station position time series Reference positions and velocities GPS station long term positions and velocties are closer to VLBI results GPS frame origins differ from SLR origin by less than 1 mm/yr for each component The GPS translation non-linear variations are still biased compared to SLR and loading model. The repeatability of GPS position time series is smaller, especially in vertical, than previous non-homegenously reprocessed solution The estimated annual variations are closer to loading model than in the past. Still larger power in horizontal for GPS. Harmonic of the draconitic frequency still visible. Their power is comparable than previous GPS solutions. Scale The scale behavior of analysis GPS reprocessed solution is stable. 31 to 40% WRMS reduction when corrected by a loading model