Deformation Modelling of the receiving unit of a VLBI radio telescope

Gravitational deformations of the receiving unit of VLBI radio telescopes systematically affect the receiving properties and cause biases in the derived products. As this deformation is unique for each radio telescope, the International VLBI Service for Geodesy and Astrometry (IVS) recommends investigations of gravitational deformation to provide correction models for VLBI data on the observation level; a challenging task for the JWG Metrology of Space Geodetic Infrastructure. Since the 1980s correction models are known and applied, that degrade the spatial problem to a two-dimensional problem, considering only homologous deformation and only taking into account three main deformation patterns. More recent studies contradict the assumption of uniform deformation and reveal more complex deformations. Therefore, identifying and modelling all relevant deformation patterns require more sophisticated analysis techniques. This contribution presents an innovative approach for modelling signal path variations using Zernike polynomials. In contrast to the conventional approach, the entire receiving structure is modelled spatially, and the analysis is not restricted to homologous deformation scenarios. Results from the analysis of the receiving unit of the 26-meter radio telescope at the Mount Pleasant Radio Observatory in Hobart, Tasmania, Australia, demonstrate the benefit of the new approach.