2024 Katherine 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.<br>This report documents the technical aspects of the local tie survey completed at the Katherine Geodetic Observatory, in the Northern Territory in October 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 2 International GNSS Service (IGS) stations (KAT1 A 59968M001, KAT2 A 59968M002), and VLBI Radio telescope (7375 A 59968S001) infrastructure.<br>In particular, this report documents the indirect measurement of the VLBI invariant reference point. Geoscience Australia has routinely performed classical terrestrial surveys at Katherine since the installation in 2010. The relationship between points of interest included the millimetre level accurate connections and their associated variance covariance matrix.