Combined Earth orientation parameters based on homogeneous and continuous VLBI and GPS data

The CONT02 campaign is of great interest for studies combining very long baseline interferometry (VLBI) with other space-geodetic techniques, because of the continuously available VLBI observations over 2 weeks in October 2002 from a homogeneous network. Especially, the combination with the Global Positioning System (GPS) offers a broad spectrum of common parameters. We combined station coordinates, Earth orientation parameters (EOPs) and troposphere parameters consistently in one solution using technique- specific datum-free normal equation systems. In this paper, we focus on the analyses concerning the EOPs, whereas the comparison and combination of the troposphere parameters and station coordinates are covered in a companion paper in Journal of Geodesy. In order to demonstrate the potential of the VLBI and GPS space-geodetic techniques, we chose a sub-daily resolution for polar motion (PM) and universal time (UT). A consequence of this solution set-up is the presence of a one-to-one correlation between the nutation angles and a retrograde diurnal signal in PM. The Bernese GPS Software used for the combination provides a constraining approach to handle this singularity. Simulation studies involving both nutation offsets and rates helped to get a deeper understanding of this singularity. With a rigorous combination of UT1–UTC and length of day (LOD) from VLBI and GPS, we showed that such a combination works very well and does not suffer from the systematic effects present in the GPS-derived LOD values. By means of wavelet analyses and the formal errors of the estimates, we explain this important result. The same holds for the combination of nutation offsets and rates. The local geodetic ties between GPS and VLBI antennas play an essential role within the inter-technique combination. Several studies already revealed non-negligible discrepancies between the terrestrial measurements and the space-geodetic solutions. We demonstrate to what extent these discrepancies propagate into the combined EOP solution.

[1]  Combination studies using the CONT02 campaign , 2005 .

[2]  Richard S. Gross,et al.  A Kalman-filter-based approach to combining independent Earth-orientation series , 1998 .

[3]  Helmut Moritz,et al.  Earth Rotation: Theory and Observation , 1987 .

[4]  Richard S. Gross,et al.  Combinations of Earth-orientation measurements: SPACE97, COMB97, and POLE97 , 2000 .

[5]  M. Rothacher,et al.  Tropospheric parameters: combination studies based on homogeneous VLBI and GPS data , 2007 .

[6]  A. Grossmann,et al.  Cycle-octave and related transforms in seismic signal analysis , 1984 .

[7]  Combination of Earth Orientation Parameters , 2005 .

[8]  D. Gambis,et al.  Monitoring Earth orientation using space-geodetic techniques: state-of-the-art and prospective , 2004 .

[9]  M. Watkins,et al.  Diurnal and Semidiurnal Variations in Earth Orientation Determined from Lageos Laser Ranging , 1994 .

[10]  L. Mervart,et al.  Bernese GPS Software Version 5.0 , 2007 .

[11]  D. Gambis.  On the possibility of detecting some terms of the diurnal polar motion by the study of satellite orbits , 1986 .

[12]  Daniel S. MacMillan,et al.  CORE Operation Center Report , 2004 .

[13]  Detlef Angermann,et al.  ITRS Combination Centre at DGFI - A terrestrial reference frame realization 2003 , 2004 .

[14]  T. Herring,et al.  Measurement of diurnal and semidiurnal rotational variations and tidal parameters of Earth , 1994 .

[15]  Zuheir Altamimi,et al.  Is there utility in rigorous combinations of VLBI and GPS Earth orientation parameters? , 2005 .

[16]  Pascal Willis,et al.  Terrestrial reference frame requirements within GGOS perspective , 2005 .

[17]  Markus Rothacher,et al.  Estimation of nutation using the Global Positioning System , 1999 .

[18]  Gerard Petit,et al.  IERS Conventions (2003) , 2004 .

[19]  G. Beutler,et al.  Analysis of the first year of Earth rotation parameters with a sub-daily resolution gained at the CODE processing center of the IGS , 2000 .

[20]  Johannes Boehm,et al.  OCCAM v.6.0 Software for VLBI Data Analysis , 2004 .

[21]  Elmar Brockmann,et al.  Combination of solutions for geodetic and geodynamic applications of the Global Positioning System (GPS). , 1997 .

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

[23]  Jim R. Ray,et al.  Evaluation of co-location ties relating the VLBI and GPS reference frames , 2005 .