SC 1.4 - Interaction of Celestial and Terrestrial Reference Frames

WG 1.4.2: Co-location on Earth and in Space for the Determination of the Celestial Reference Frame



Chair: Sebastien Lambert (France)

Very Long Baseline Interferometry (VLBI) is the only technique sensitive to the "quasi inertial" celestial reference frame, and the most recent realization of the International Celestial Reference System, the ICRF2, was determined in a VLBI-only solution. The other space geodetic techniques (GNSS, DORIS, SLR) define a dynamical celestial reference frame, but all techniques are combined to determine the International Terrestrial Reference Frame (ITRF) without adding the estimation of sources to that combination, thus causing inconsistencies between the ICRF and the ITRF.

The goal of WG 1.4.2 is to investigate the impact on the ICRF when combining VLBI observations with those from satellite techniques. Historically, this combination is based on local tie information at the co-location sites, but in future also troposphere ties and even space ties could be used, i.e., observing the GNSS constellation or a dedicated micro satellite like GRASP with VLBI, so that a fully consistent system is created.


  • Support the realization of a full combination of the VLBI/GNSS/DORIS/SLR at the normal equation level including estimates of radio source coordinates. This should be done in close cooperation with the IERS Working Group on the Combination at the Observation Level.
  • Investigate various analysis options (local and troposphere ties, twin telescopes) on the results (TRF, EOP, CRF).
  • Analyze VLBI observations to GNSS satellites.
  • Simulate the effect of VLBI observations to GNSS and SLR satellites and assess the impact on the CRF.
  • Simulate future micro satellite missions like GRASP in VLBI analysis software packages.
  • Simulate the benefits of the upcoming VLBI2010 equipment to propose recommendations for the near future.


S. Lambert (France)

Z. Malkin (Russia)

C. Ma (USA)

J. Böhm (Austria)

R. Haas (Sweden)

R. Heinkelmann (Geodesy)

Y. Kwak (Korea)

Le Poncin-Lafitte

L. Plank (Austria)

M. Seitz (Germany)

V. Tornatore (Italy)



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