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Geodetic Reference Frames In Presence of Crustal Deformations

Geodetic Reference Frames In Presence of Crustal Deformations. Martin Lidberg 1,2 , Maaria Nordman 3 , Jan M. Johansson 1,4 , Glenn A Milne5, Hans-Georg Scherneck 1 , Jim L Davis 6 1 Onsala Space Observatory, Chalmers, Sweden 2 Lantmäteriet (National Land Survey of Sweden)

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Geodetic Reference Frames In Presence of Crustal Deformations

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  1. Geodetic Reference Frames In Presence of Crustal Deformations Martin Lidberg1,2, Maaria Nordman3, Jan M. Johansson1,4, Glenn A Milne5, Hans-Georg Scherneck1, Jim L Davis6 1Onsala Space Observatory, Chalmers, Sweden 2Lantmäteriet (National Land Survey of Sweden) 3Finnish Geodetic Institute, Finland 4Swedish National Testing and Research Institute 5University of Durham, UK 6Harvard-Smithsonian Centre for Astrophysics EGU 2008, 14-18 April, Vienna, Austria

  2. Effects of the land uplift • First determination of the land uplift related to sea level •  apparent • land uplift • Determination of horizontal rates and absolute land uplift values; • the purpose of BIFROST

  3. Outline • The BIFROST GPS network • GPS analysis • Reference frame realization • Time series analysis and data editing • Evaluation of the velocity field • Address noticed problems and possible causes • Conclusions

  4. The extended BIFROST network • The analysis includes: • Public sites from IGS and EPN (EUREF Permanent Network) (blue dots ) • Sites not in the public domain (yellow diamonds ) • Totally: 83 sites • Period of analysis: • Aug. 1993 – Oct. 2006

  5. GAMIT / GLOBK GAMIT (GPS analysis) Traditional analysis strategy 10° elevation cut off angle Trop. zenith delay & gradients the Niell 1996 mapping functions Relative antenna PCV values (“absolute” PCV not used so far) a priori orbits from SCRIPPS GLOBK (combination & ref. frame) combination of sub-networks reference frame realization. Combine the regional analysis with “complete IGS analysis” from SCRIPPS (GAMIT h-files). Satellite orbits are given loose constraints in the quasi-observations. GPS analysis strategy GIPSY • Precise Point Positioning (PPP) using JPL products • And ambiguity fixing • Used to validate the GAMIT/GLOBK solution

  6. Combination for “global solution” & reference frame realization ITRF2000: 43 “good” sites as candidates for the daily stabilization. in GLOBK. ITRF2005: 78 sites as candidates. - Include breaks from ITRF2005 coordinate list

  7. (ITRF2000)Results from stabilization (ITRF2005) Scale (ppb) postfit RMS (mm) No used sites

  8. Example of time series of GPS positions • De-trended position time series from Vilhelmina (64°N) for the complete period • Aug. 1993 – Oct 2006 • 1993-1996: • - some “bad” antenna radoms • PROBLEMS !!!??? • Non-linear time-series in the vertical: • Bent “banana”-shape ??? • - Or rate change by 2003 ??? • Tide model problem?? • Watson, Tregoning, Coleman (2006) “Impact of solid earth tide models on GPS coord. and trop. time series”, GRL.

  9. New combination - with my own global analysis • The global network: • 35 selected sites. (black squares ) • - Cover the globe - Connect regional & global analysis • - Include “good” sites for reference frame realization • Reference frame sites: • 23 sites as candidates (yellow circles )

  10. Combined Regional BIFROST + “35-site” global - Vertical “banana-shape” heavily reduced!!! (maybe not eliminated..) - In the analysis we have “stable” sites with +10 yr observations, and “new” sites (< 5 yr). Two step reference frame approach 1. Determine pos+vel for 27 “good sites” (Swe+Fin+some EPN) from “stable” period 1998 to 2004 (7yr). 2. Apply 6-par transf. (no scale) of all daily solutions to the “regional” frame defined above.

  11. After common mode reduction using daily transformations

  12. Derived velocity field relative to Eurasia Red: ITRF2000 (eura) Green: ITRF2005 (eura) ITRF2000: removed the Eurasia plate tectonic motion using the ITRF2000 Euler pole for Europe ITRF2005: transformed (rotated) to the ITRF2000_eura velocities RMS of velocity at 7 European IGS sites: 0.5 mm/yr level -> suggest a successful reference frame realization. For POTS and METS; “my” velocities and official ITRF2005 agree by: North: 0.2 mm/yr East: 0.3 mm/yr Up: 0.3 mm/yr

  13. Glacial Isostatic Adjustment (GIA) Glaciations cause change of load from ice and ocean to the earth. This load cause deformation of the earth shape and mass re-distribution. Updated GIA model (Milne et al 2001) Ice history model from Lambeck 120 km lithosphere, upper mantle visc. 51020 Pas lower mantle visc. 51021 Pas Thanks Glenn Milne, Maaria Nordman, Pippa Whitehouse!!

  14. Vertical velocity • ITRF2005 • ITRF2000 • GIA model • Ekman (1998) based on: • mareographs and levellings, • 1.2 mm/yr eustatic sea level rise • change of the geoid based on Ekman & Mäkinen (1998) • Compared to the ITRF2000 • values: • mean Std (mm/yr) • ITRF2005 0.4 0.1 • GIA model -0.4 0.5 • Ekman -0.4 0.6

  15. The new station velocities Validation using GIPSY (0.1, 0.1, 0.2) (n,e,u) mm/yr New GIA model minus GPS, “best sites” (0.3, 0.2, 0.3) (n,e,u) mm/yr The new GAMIT/GLOBK solution (in ITRF2005) And GIA model

  16. The “hole” in the sky plot at high latitude sites! • Satellite geometry at two locations • Will this cause error in height, if e.g. elevation dependence (antenna models) and mapping functions are imperfect?

  17. Vilhelmina, 64°N BIFROST+ global SOPAC IERS1996 tide model Relative antenna models BIFROST+ Own global 35 site net Mixed IERS1996+ IERS2003 tide model Relative antenna models 45 global+35 EPN sites IERS2003 tide model Absolute antenna models GMF mapping function (Only every 10 day)

  18. Conclusion and outlook GPS-velocities and GIA-model agree at - 0.4 mm/yr level (1) horizontal - 0.5 mm/yr level (1) vertically  GIA model explain observed velocities to 0.5 mm/yr!! OK for coordinate transformation and “geo-referencing” purposes;but for sea level work (exploring GPS and Tide gauge obs.) we must be careful and continue the work regarding: • “long term stability in GNSS results” • improvements in the reference frame! in order to reached the 0.1 mm/yr goal! Proper velocity estimation need correct models in the GPS analysis! • Therefore the re-processing of IGS, with “best” models is very important (abs. antenna models, tide model, mapping function, ionosphere..) • Will be a base for the next improved ITRF200x!

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