Very Long Baseline Interferometry (VLBI) is the only technique directly connecting the terrestrial reference frame (TRF) with the celestial reference frame (CRF) via estimates of nutation and the Earth rotation parameters, in particular the Earth’s rotational velocity: UT1-UTC.

DGFI is one of six operational International VLBI Service for Geodesy and Astrometry (IVS) Analysis Centers, on which the official products of IVS and partly of IERS are based on. As such it is actively contributing to operational products as well as participating in temporarily projects and working groups of IVS, such as the IERS/IVS Working Group on the Second Realization of the International Celestial Reference Frame ICRF2. The analysis is currently concerned with the determination of session-wise normal equations in SINEX-format with a relatively short time lag and of special tropospheric solutions in quasi-SINEX-format.

The VLBI data analysis software OCCAM has been jointly developed together with Geoscience Australia and the Institute for Geodesy and Geophysics, Vienna Technical University. The program code is updated whenever new conventional models or standards are released. The current version is under a complete revision and is going to become a part of DGFI Orbit- und Geodätische Parameterbestimmungssoftware (DOGS) enabling a simultaneous analysis of VLBI and SLR data.

Deformations of the terrestrial reference frame can cause deformations of the celestial reference frame and vice versa. Interactions between the reference frames (IAG SC 1.4) thus represent another major topic of DGFI’s science related to VLBI data analysis. To prevent indirect deformations, the individual effects have to be identified, quantified and finally corrected (see figure).