Impact of loading effects on determination of the International Terrestrial Reference Frame

The International Terrestrial Reference Frame (ITRF), as a realization of the International Terrestrial Reference System (ITRS), is represented by a set of station positions and linear velocities. They are intended to be used as regularized coordinates to which some corrections should be added to access instantaneous coordinates. The latest ITRS realization is the ITRF2005, which has integrated time series of station positions to form long-term solutions for the four space geodetic techniques. Currently, a purely linear model is used to parameterize station displacements in the estimation process, plus occasional discontinuities in case of earthquakes or equipment changes. However the input data have been derived without applying surface loading models and so surface loading effects are supposed to be embedded in the coordinates as measured quantities. We evaluate the effect of applying a posteriori loading corrections, which include the effect of atmospheric, non-tidal ocean, and continental water loading, to time series of positions estimated from Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Global Positioning System (GPS) data. We notice that they reduce about 50% or more of the annual signals in the translation and scale parameter time series of the SLR and VLBI techniques, except in SLR Z translation. In general, the estimated secular frame definition is negligibly affected and estimated positions and velocities are not significantly modified for stations that have accumulated a large number of observations. A multi-technique combination of such derived frames allows concluding that, for some cases, loading model corrections might degrade co-located station coordinates almost as much as they benefit them. However, most significant improvement of the estimated secular coordinates is observed for stations with less than 100 estimated positions as demonstrated with a multi-technique combination.

[1]  W. Farrell Deformation of the Earth by surface loads , 1972 .

[2]  G. Blewitt Self‐consistency in reference frames, geocenter definition, and surface loading of the solid Earth , 2003 .

[3]  Gerd Gendt,et al.  The International GPS Service: Celebrating the 10th anniversary and looking to the next decade , 2005 .

[4]  Derek D. Lichti,et al.  Investigating the propagation mechanism of unmodelled systematic errors on coordinate time series estimated using least squares , 2005 .

[5]  Pascal Gegout,et al.  GGFC Special Bureau for Loading: current status and plans , 2003 .

[6]  M. Watkins,et al.  GRACE Measurements of Mass Variability in the Earth System , 2004, Science.

[7]  Dirk Behrend,et al.  The International VLBI Service for Geodesy and Astrometry (IVS): current capabilities and future prospects , 2007 .

[8]  T. van Dam,et al.  Effects of atmospheric pressure loading and seven-parameter transformations on estimates of geocenter motion and station heights from space geodetic observations , 2005 .

[9]  Michael R Pearlman,et al.  THE INTERNATIONAL LASER RANGING SERVICE , 2007 .

[10]  P. Milly,et al.  Global Modeling of Land Water and Energy Balances. Part III: Interannual Variability , 2002 .

[11]  R. Ferland,et al.  The IGS-combined station coordinates, earth rotation parameters and apparent geocenter , 2009 .

[12]  Axel Nothnagel,et al.  The contribution of Very Long Baseline Interferometry to ITRF2005 , 2007 .

[13]  P. English,et al.  GPS observation of compaction or expansion of the Perth basin aquifer system , 2007 .

[14]  Peter Steigenberger,et al.  Reprocessing of a global GPS network , 2006 .

[15]  Harald Schuh,et al.  Impact of Analysis Options on the TRF, CRF and Position Time Series Estimated from VLBI , 2006 .

[16]  Zuheir Altamimi,et al.  ITRF2000: A new release of the International Terrestrial Reference Frame for earth science applications , 2002 .

[17]  Thomas A. Herring,et al.  Detection of atmospheric pressure loading using very long baseline interferometry measurements , 1994 .

[18]  Y. Bock,et al.  Anatomy of apparent seasonal variations from GPS‐derived site position time series , 2001 .

[19]  Geoffrey Blewitt,et al.  Effect of annual signals on geodetic velocity , 2002 .

[20]  P. Milly,et al.  Global Modeling of Land Water and Energy Balances. Part I: The Land Dynamics (LaD) Model , 2002 .

[21]  Xavier Collilieux Analyse des séries temporelles de positions des stations de géodésie spatiale : application au Repère International de Référence Terrestre (ITRF) , 2008 .

[22]  Jan Kouba,et al.  Testing of global pressure/temperature (GPT) model and global mapping function (GMF) in GPS analyses , 2009 .

[23]  J. Ray,et al.  Effect of the satellite laser ranging network distribution on geocenter motion estimation , 2009 .

[24]  Peter Steigenberger,et al.  Comparison of GMF/GPT with VMF1/ECMWF and implications for atmospheric loading , 2009 .

[25]  Z. Altamimi,et al.  ITRF2005 : A new release of the International Terrestrial Reference Frame based on time series of station positions and Earth Orientation Parameters , 2007 .

[26]  T. van Dam,et al.  Displacements of the Earth's surface due to atmospheric loading: Effects on gravity and baseline measurements , 1987 .

[27]  Axel Nothnagel,et al.  Conventions on thermal expansion modelling of radio telescopes for geodetic and astrometric VLBI , 2009 .

[28]  H. Schuh,et al.  Troposphere mapping functions for GPS and very long baseline interferometry from European Centre for Medium‐Range Weather Forecasts operational analysis data , 2006 .

[29]  Xavier Collilieux,et al.  Comparison of very long baseline interferometry, GPS, and satellite laser ranging height residuals from ITRF2005 using spectral and correlation methods , 2007 .

[30]  Geoffrey Blewitt,et al.  Crustal displacements due to continental water loading , 2001 .

[31]  J. Ray,et al.  Anomalous harmonics in the spectra of GPS position estimates , 2008 .