Measurement of Earth's Nutation by VLBI: Direct Estimates from VLBI Delays and a Discussion on the Error

Accurate measurements of the Earth nutation by VLBI provide insights into the deformability of and the coupling mechanisms at the core-mantle and core-inner core boundaries. We propose here to adjust nutation amplitudes directly to VLBI delays, as opposed to the traditional method consisting of fitting nutation amplitudes to time-domain nutation series. However, the complexity of the VLBI analysis chain makes the formal error on the parameters somehow obscure and disconnected from a realistic error based on, e.g., empirical tests of robustness and errors on models. In this work, we address some striking differences between formal and empirical errors.