Continuous monitoring surveys of the Hobart AuScope VLBI Antenna

Jim Lovell, School of Maths and Physics, University of Tasmania Christopher Watson, School of Geography and Environmental Studies, University of Tasmania Alistair Cole, School of Geography and Environmental Studies, University of Tasmania Stas Shabala, School of Maths and Physics, University of Tasmania Jamie McCulum, School of Maths and Physics, University of Tasmania John Dickey, School of Maths and Physics, University of Tasmania

The Australian AuScope VLBI array incorporates three new 12 m radio telescopes at Hobart (Tasmania), Yaragadee (Western Australia) and Katherine (Northern Territory). Following the end of the commissioning phase, the Hobart telescope undertook its first IVS observations in October 2010. An important focus of recent activity has been the design and implementation of a monitoring system to assess the deformation of the telescope invariant point (IVP) at each site in the AuScope array. The primary aim of this study is to utilize continuous observations from a Leica TDRA6000 total station to characterize the deformation of the IVP as a function of time, temperature and orientation. In this contribution, we present our approach and provide initial results for surveys undertaken at the Hobart Mt Pleasant observatory. Our system includes the observation of temperature throughout the telescope structure (including its foundation), whilst a Finite Element Analysis (FEA) enables the thermal response of the structure to be modeled against the observed thermal profile. Our terrestrial survey design has an emphasis on the calibration of incidence angle effects on our chosen targets which are Leica 0.5" Tooling Ball Reflectors (TBRs). We adapt code provided by Schmeing et al to achieve a continuous monitoring capability to a series of targets mounted on custom mounts over the telescope, in addition to its foundation, and other local geodetic reference marks. We conclude with the presentation of the expected (modeled) thermal response of the telescopes at Yaragadee and Katherine, both areas that exhibit significant diurnal and seasonal temperature variation.