2024 Yarragadee Geodetic Observatory Co-Location Local Tie Survey Technical Report

The integrity and strength of multi-technique terrestrial reference frames, such as realisations of the International Terrestrial Reference Frame (ITRF), depend on the precisely measured and expressed local-tie connections between space geodetic observing systems at co-located observatories. Australia has several observatories which together host the full variety of space geodetic observation techniques, including Global Navigation Satellites Systems (GNSS), Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) beacons.This report documents the technical aspects of the local tie survey completed at the Yarragadee Geodetic Observatory, in Western Australia in June 2024. The aim of the survey was to precisely measure the local terrestrial connections between the space-based geodetic observing systems co-located at the observatory, which include 3 International GNSS Service (IGS) stations (YARR A 50107M006, YAR2 A 50107M004, YAR3 A 50107M008), SLR (YIVP A 50107S007) and DORIS (YASB A 50107S011) and VLBI Radio telescope (7376 A 50107S012) infrastructure.In particular, this report documents the indirect measurement of the VLBI & SLR invariant reference point. Geoscience Australia has routinely performed classical terrestrial surveys at Yarragadee, including surveys in 1998, 2001, 2003, & 2007, and surveys have been completed at the site since the SLR installation in the 1970s. A high precision survey was conducted between the survey pillars surrounding the SLR observatory. These survey pillars were monitored to ensure their stability as part of a consistent, stable terrestrial network from which local tie connections were made to the SLR and other observing systems. The relationship between points of interest included the millimetre level accurate connections and their associated variance covariance matrix.