1 / 27

Outline

Session 2: Strenghts, weaknesses, modelling standards and processing strategies of space geodetic techniques.

gavin
Download Presentation

Outline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Session 2:Strenghts, weaknesses, modelling standardsand processing strategies of space geodetic techniques Recent Results from the IGSTerrestrial Frame Combinations__________________________________________________________________________________________________Elaboration of IGS08Paul Rebischung, Bruno Garayt REFAG Symposium 6 October 2010 – Marne-la-Vallée, France

  2. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France Outline • The IGS terrestrial frame combinations: • Presentation • Methodology • Results • Prospects • IGS08: • Definition • Availability over time • IGS08 core network

  3. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France TF combination: Products • Weekly combined solution: • Combination of 9 AC solutions • Station positions • ERP (XPO, XPOR, YPO, YPOR, LOD) • « Apparent geocenter » • Cumulative solution: • Stacking of the weekly solutions • Station positions at 2005.0 and velocities • Updated each week NRCAN since 1999 IGN since 2010

  4. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France TF combination: Network

  5. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France TF combination: Methodology • Preparation of AC solutions: • Remove constraints → Unconstrained, singular normal matrices • Fix some parameters (UT, satellite PCOs) • Solve normal equations by adding minimal constraints • Iterative combinations of AC solutions • Estimated parameters: • Combined station coordinates and ERP • « AC → combined » transformation parameters • Internal constraints ⇒ Combined solution is in a mean frame. • Rejection of outliers (5 cm / 5 σ) • Update of AC variance factors • Final combination with transformation parameters fixed • Explicitation of combined geocenter • Alignment to IGS05

  6. W. avg. of AC residuals TF combination: Results Std. dev. of AC residuals Excellent agreement with ‘mig’: < 0.5 mm in horizontal< 1 mm in vertical ⇒ Independent validation of the combination Global level of agreement between AC solutions: • 1-2 mm in horizontal• 2-5 mm in vertical Change in the combination method REFAG Symposium 6 October 2010 – Marne-la-Vallée, France

  7. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France

  8. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France TF combination: How to progress? • Need to understand the discrepancies between AC frames ⇒ Maps of the « AC – igs » residuals

  9. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France Mean SH fits of « AC-igs » residuals over weeks 1548-1599 COD GFZ MIT EMR GRG NGS ESA JPL SIO

  10. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France TF combination: How to progress? • Study the « AC distorsions » over 1994 – 2010(using repro1) • Replace the cumulative solution by a new onebased on repro1 • Study « AC – cumulative solution » residuals in the frequency domain • Study the geocenter discrepancies

  11. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08 • IGS realization of ITRF2008: • Will become the Reference Frame of IGS products. ⇒ Consistency and stability of IGS products will critically depend on IGS08. • Will be used by many GNSS users to access ITRF2008. • Initially intended to be a subset of “good” GNSS stations from ITRF2008 • But because of new antenna robot calibrations included in igs08.atx,small shifts will be applied to the ITRF2008 coordinates of some stations. • Unlike IGS05, IGS08 should include RF stationsback to 1994 (for repro2).

  12. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08: Selection criteria • Geographical location • “ITRF2008 quality”: • Data span (5 years at least) • Maximal time spans between two discontinuities (3 years at least) • Number of discontinuities (5 at most) • Absence of velocity discontinuities • Standard deviation of last velocity (0.3 mm/y at most) • Residual time series (RMS + visual inspection) • Equipment: • Type of antenna calibration • GPS+GLONASS capability • Presence of an external atomic clock • Co-location with other techniques • Belonging to IGS05

  13. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08: Result of the selection • 241 stations • Global coverage • But densityheterogeneities

  14. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08: Availability over time

  15. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France Aliasing of loading signals • Weekly solutions are aligned to IGSxx. • Helmert parameters absorb part of the loading signals. ⇒ Station annual signals are reduced/amplified and/or shifted. • This aliasing can be reduced by using a well distributed RF (Collilieux, 2010). ⇒ « IGS08 core network »

  16. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08 core network

  17. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France Thanks for your attention!

  18. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France Backup slides

  19. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France TF combination: Methodology • Variance component estimation: • A priori: variance factors from previous week • After each iteration: • : weighted squared sum of solution s residuals • : redundancy factor of solution s • : number of observations from solution s • : design matrix of solution s • : combined covariance matrix

  20. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France RF combination: Methodology • Paradox of the combined geocenter: • Rigorous geocenter combination ⇒ No translation parameters • But… • In practice, AC solutions are brought to the same framebefore geocenter is combined. ⇒ Estimated precision is too optimistic (usually [1 mm ; 1 mm ;3 mm]). • To be used with care! • There is still a long way before GNSS can contribute to the ITRF origin.

  21. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08: Selection criteria Distribution of GNSS stations among IGS stations in ITRF2008

  22. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08: Selection criteria Distribution of antenna calibration types among IGS stations in ITRF2008

  23. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08: Availability over time

  24. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France New antenna calibrations • New robot calibrations by Geo++ available for igs08.atx • But repro1 (input for ITRF2008) computed with old calibrations • To ensure consistency between IGS08 & igs08.atx: • Drop affected stations from IGS08 • Apply shifts to the ITRF2008 coordinates of these stations Same problem as the transition from ITRF2005, relative calibrations to IGS05, absolute calibrations

  25. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France New antenna calibrations • To estimate coordinate shifts due to calibration changes, • PPP tests were performed at IGN, ESA and CNES. • ACs provided parallel solutions using the new calibrations. • Good global agreement • But for certain antenna types, fixing ambiguities or not seems to have an impact on the estimated shifts. • When possible, IGN PPP shifts will be applied.

  26. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08 core network • Simulations performed by Xavier Collilieux: Differences at the annual frequency between the true values and the residuals of the 7-parameter transformation: ⇒ Annual signals are better retrieved if « IGS08 core » is used instead of IGS08. North Height East x(t) = In cos(ωt) + Out sin(ωt)

  27. REFAG Symposium 6 October 2010 – Marne-la-Vallée, France IGS08 core network • Simulated translations and scale factor: Full IGS08 IGS08 core Loading model including: - Atmospheric loading - Non-tidal ocean loading - Continental water loading (T. van Dam, University of Luxembourg)

More Related