Simulating the effects of quasar structure on parameters from geodetic VLBI

We investigate the effects of quasar structure on geodetic very long baseline interferometry (VLBI) measurements. We create catalogues of simulated and real quasars with a range of structure indices, and use these to generate synthetic CONT11 observations with the Vienna VLBI Software simulator tool. We systematically investigate the effects of quasars with different amounts of source structure, and find that source structure can affect station positions at the one-millimetre level. This effect is stronger for isolated stations. Overall, source structure is found to contribute to about 10 % of the troposphere and clock effects. Our simulations confirm analytical predictions that source structure mitigation strategies must be developed in order to achieve millimetre-level VLBI position accuracy.