VLBI for Geodesy and Geodynamics

In geodetic and geodynamic applications, Very Long Baseline Interferometry is first and foremost appreciated for its capability to provide direct geometrical ties to the quasi-inertial system of extragalactic radio sources. Geodetic VLBI can measure Earth rotation and orientation as well as precise station positions and their velocities without involving the gravity field of the Earth. In the broader context of Earth observation and the monitoring of geodynamic processes, these and many more unique features have allowed the VLBI-technique to achieve pioneering feats such as the determination of present-day plate tectonic motions, post glacial rebound, sub-daily Earth rotation variations and parameters of general relativity. The principal elements of the geodetic approach to VLBI as well as its relation to other space techniques will be at the center of this chapter.