Slide 1

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 Lantmteriet (National Land Survey of Sweden) 3 Finnish Geodetic Institute, Finland 4 Swedish National Testing and Research Institute 5 University of Durham, UK 6 Harvard-Smithsonian Centre for Astrophysics EGU 2008, 14-18 April, Vienna, Austria Slide 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 Slide 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 Slide 4 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 The extended BIFROST network Slide 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 Slide 6 ITRF2000: 43 good sites as candidates for the daily stabilization. in GLOBK. ITRF2005: 78 sites as candidates. - Include breaks from ITRF2005 coordinate list Combination for global solution & reference frame realization Slide 7 (ITRF2000) Results from stabilization (ITRF2005) Scale (ppb) postfit RMS (mm) No used sites Slide 8 Example of time series of GPS positions De-trended position time series from Vilhelmina (64N) 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. Slide 9 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 ) New combination - with my own global analysis Slide 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. Slide 11 After common mode reduction using daily transformations Slide 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 Slide 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 10 20 Pas lower mantle visc. 5 10 21 Pas Thanks Glenn Milne, Maaria Nordman, Pippa Whitehouse!! Slide 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 & Mkinen (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 Slide 15 The new GAMIT/GLOBK solution (in ITRF2005) And GIA model 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 Slide 16 Satellite geometry at two locations Will this cause error in height, if e.g. elevation dependence (antenna models) and mapping functions are imperfect? The hole in the sky plot at high latitude sites! Slide 17 Vilhelmina, 64N 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) Slide 18 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! Conclusion and outlook