Local Tie Technical Report 3 Summary

The combination of Space Geodetic techniques is fundamental to the definition of the International Terrestrial Reference Frame (ITRF). An integral component of this combination is the accurate connection between the different techniques, commonly referred to as the local tie. As the achievable accuracy of the space geodetic techniques increase, the need for these highly accurate local ties becomes imperative. The observation of the local ties at the 1-2 mm level also allows the monitoring of site deformation consequently.

Australia, due largely to its southern location, is home for the full range of space geodetic techniques, principally located at five sites. AUSLIG (now Geoscience Australia) maintains the local ties at these five sites throughout Australia. At each of these sites, a network of survey marks allows an accurate and over-determined survey to be observed. The results of these surveys are the vectors between the primary monument and other significant points at each site. In the case of Very Long Baseline Interferometry (VLBI) antennae and Satellite Laser Ranging (SLR) telescopes, the point of interest is referred to as an invariant point (IVP). This IVP is different for each of the antennae/telescopes and needs to be determined by indirect observation, since generally the IVP is inaccessible. A description of the IVP at each site is given in the result section of this report.

The survey of these local ties generally needs to be repeated on a two yearly basis (International Laser Ranging Service recommendation), depending on the stability of the site. The results listed for Tidbinbilla and Hobart in this report are from observations taken in 1995. Mt Stromlo, Yarragadee (Moblas 5) and Orroral had observations taken in 1998 and 1999. In the case of Orroral these observations constitute the final survey of the station, since it was decommissioned in November 1998. The Mt Stromlo survey presented here is the first undertaken by AUSLIG (now Geoscience Australia) for this site. A contractor to Electro Optic Systems (EOS) undertook a previous survey, however the results were never submitted to International Earth Rotation and Reference Systems Service (IERS) by AUSLIG (now Geoscience Australia). For all five sites, comparisons to previous results are tabulated in the relevant Appendix.

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