Simulation of VLBI Observations to Determine a Global TRF for GGOS

In this study, we present a global terrestrial reference frame (TRF) from simulated very long baseline interferometry (VLBI) observations. In the time span from 2008 until 2014, 695 standard VLBI rapid turnaround (R1, R4) 24 h-sessions were simulated using a network of 28 globally distributed stations. Within the software VieVS@GFZ, we apply different measurement noise at the observation level and investigate the impact on the TRF and on the Earth rotation parameters. We find that the effect of varying only the noise applied within the simulation is not proportional to the changes in the estimates and their uncertainties. For instance, increasing the noise level from 15 ps to 300 ps increases the uncertainty of the station positions by a factor of 3.5, of station velocities by 5, of polar motion by 3.4, and of UT1-UTC by 1.5. A comparison with the VLBI-TRF derived from real observations within the same time span shows that the solution simulated with a noise level based on the formal errors of real observations is still too optimistic.