IGS Analysis Center Workshop, 2-6 June 2008, Florida, USA GPS in the ITRF Combination D. Angermann, H. Drewes, M. Krügel, B. Meisel Deutsches Geodätisches.

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<ul><li><p>IGS Analysis Center Workshop, 2-6 June 2008, Florida, USA GPS in the ITRF CombinationD. Angermann, H. Drewes, M. Krgel, B. MeiselDeutsches Geodtisches Forschungsinstitut, MnchenE-Mail: angermann@dgfi.badw.de</p></li><li><p>OutlineITRS Combination Center at DGFIInput data for TRF computationsAnalysis and accumulation of GPS time series GPS in the inter-technique combination Contribution of GPS to the datum realizationConclusions and outlook</p></li><li><p>ITRS Combination Center at DGFI General concept: Combination on the normal equation level Software: DGFI Orbit and Geodetic Parameter Estimation Software (DOGS)Geodeticdatum</p></li><li><p>Input data sets for TRF computations (1/2)ITRF2005: Time series of station positions and EOPITRF2005 data sets are not fully consistent, the standards andmodels were not completely unified among analysis centersShortcomings concerning GPS: IGS solutions are not reprocessed (e.g., model and software changes) Relative antenna phase center corrections were applied </p><p>Techn.Service / ACDataTime PeriodGPSIGS / NRCanweekly solutions1996 - 2005VLBIIVS / IGG24 h session NEQ1984 - 2005SLRILRS / ASIweekly solutions1993 - 2005DORISIGN - JPL/LCA weekly solutions1993 - 2005</p></li><li><p>Input data sets for TRF computations (2/2)GGOS-D: Time series of station positions and EOPImprovements of GGOS-D data compared to ITRF2005: Homogeneously processed data sets - Identical standards, conventions, models, parameters - GPS: PDR (Steigenberger et al. 2006, Rlke et al. 2008) Improved modelling - for GPS: absolute instead of relative phase centre corr. - for VLBI: pole tide model was changedGGOS-D: German project of BKG, DGFI, GFZ and IGG funded by BMBF</p><p>Techn.InstitutionsData Time PeriodGPSGFZdaily NEQ1994 - 2007VLBIIGG / DGFI24 h session NEQ1984 - 2007SLRDGFI / GFZweekly NEQ1993 - 2007</p></li><li><p>TRF computation strategyFirst step: Analysis of station coordinate time series and computation of a reference frame per techniqueModelling time dependent station coordinates by </p><p> epoch positions linear velocities - (seasonal signals)- discontinuitiesSecond step: Combination of different techniques by- relative weighting- selection of terrestrial difference vectors (local ties)- combination of station velocities and EOP- realization of the geodetic datum</p></li><li><p>TRF per technique (1/4) Instrumentation changes Earthquakes Seasonal variationsAnalysis of GPS station position time seriesITRF2005. 221 discontinuities in 332 GPS stations (1996 - 2005)GGOS-D: 95 discontinuities in 240 GPS stations (1994 - 2007)</p></li><li><p>TRF per technique (2/4)Effect of annual signals ?Equating of station velocities ?Sol. ID 1Sol. ID 2Velocity differences w.r.t. a linear modelGPS station Irkutsk (Siberia)GPS station Hofn (Iceland)1997 2000 2003 20061997 2000 2003 2006</p><p>SolutionIDVelocities[mm/yr]Sol. ID 1Sol. ID 24.5 0.98.7 0.7 (2 1)4.2 1.2</p><p>obs time span [yrs]0.51.02.03.0 velocities [mm/yr]-37.5 3.2-3.7 2.32.7 0.8-0.3 0.5</p></li><li><p>TRF per technique (3/4)Seasonal signals - Comparison with geophysical dataModels consideratmospheric,oceanic and hydrologic mass loads:</p><p>NCEP, ECCO,GLDASPotsdamKrasnoyarskBahrainCorrelation coefficient = 0,50Correlation coefficient = 0,79Correlation coefficient = 0,731997 1999 2 001 2003 2005[cm] 2 0-2 2 0-2 2 0-2</p></li><li><p>TRF per technique (4/4)Shape of seasonal signals can be approximated by sine/cosine annual and semi-annual functionsBrasiliaAnkaraEstimation of annual signals in addition to velocities ?Advantages: Improved velocity estimation Better alignment of epoch solutionsDisadvantages / open questions: More parameters (stability) ? Seasonal signal geophysically meaningful ? How to parameterize seasonal signals ?</p></li><li><p>Computation of the TRF (1/3)Selection of local ties at co-location sitesSLR-VLBI (9)SLR-GPS (25)VLBI-GPS (27)</p></li><li><p>Computation of the TRF (2/3)ITRF2005GGOS-DSelection of terrestrial difference vectors (1)</p><p>Three-dimensional differences between space geodetic solutions (GPS and VLBI) and terrestrial difference vectors [mm]= stations in southern hemisphereKrgel et al. 2007: Poster presented at AGU Fall Meeting 2007</p></li><li><p>Computation of the TRF (3/3)Selection of terrestrial difference vectors (2)</p><p>Mean pole differenceNetwork deformation</p><p>Mean pole difference: 35 mas (1 mm)</p><p>Network deformation: 0.3 mm</p><p>Number of co-locations: 19</p><p>ITRF2005:</p><p>Pole difference: 41 mas</p><p>Deformation: 1.0 mm</p><p>No. co-locations: 13</p></li><li><p>Realization of the geodetic datum (1/4)</p><p>ITRF2005D(DGFI Solution)GGOS-DOriginSLRSLRScaleSLR + VLBISLR + VLBI + GPS OrientationNNR conditionsw.r.t. ITRF2000NNR conditionsw.r.t. ITRF2005Orientationtime evolutionNNR conditions w.r.t. horizontal motions by using the Actual Plate Kinematic andDeformation Model (APKIM)</p></li><li><p>Realization of the geodetic datum (2/4)Station velocity residuals for 56 core stations used to realize the kinematic datum of the ITRF2005D solution w.r.t. APKIM</p></li><li><p>Realization of the geodetic datum (3/4)Translation and scale estimates of similarity transformations between combined PDR05 and weekly solutions (Rlke et al., JGR 2008) </p></li><li><p>Realization of the geodetic datum (4/4)Cdatum = (GT CGPS-1 G)-1Method:CGPS: Covariance matrix of GPS solution (loose constrained)G:Coefficients of 7 parameter similarity transformation matrixCdatum:Covariance matrix of datum parametersDatum information of GPS observations (compared to SLR)Standard deviations for datum parameters [mm]</p><p>txtytzscaleGPS0.70.71.10.2SLR1.00.92.72.9</p></li><li><p>Conclusions and outlookDiscontinuities: Number of jumps reduced due to homogeneous re- processing; discontinuity tables among techniques should be adjusted. Annual signals: Treatment of seasonal variations in station positions (e.g., by estimating sine/cosine functions) should be investigated. Co-locations: Discontinuities are critical; at least two GPS instruments should be operated at each co-location site. Geodetic datum: GPS reprocessing provides stable results for the scale and for the x- and y-component of the origin, the z-component shows large seasonal variations which should be investigated.GPS reprocessing is essential for the next ITRF (unified standards and models should be applied for different techniques). </p></li></ul>

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