Earth rotation

The rotation of the Earth varies continuously. Its rotation axis changes its orientation with respect to both a space-fixed and an Earth-fixed reference system, and the angular velocity of the rotation fluctuates with time. The knowledge and therewith the continuous observation of Earth rotation variations is important for various reasons. It is fundamental for the realisation of time systems, the accurate determination of reference frames and precise navigation by providing the link between an Earth-fixed and a space-fixed coordinate system. Moreover, time series of Earth rotation parameters are of great interest for various disciplines of geosciences and astronomy since their changes are related to gravitational and geodynamic processes in the Earth system. In this way, Earth rotation monitoring contributes significantly to the understanding of the dynamics of the Earth system and the interactions between its individual components, e.g. the exchange of angular momentum between atmosphere, ocean and solid Earth, or the coupling mechanism between the Earth's core and mantle. Today the metrological basis for this highly interdisciplinary research is provided by precise space geodetic techniques such as Very Long Baseline Interferometry (VLBI), Satellite/Lunar Laser Ranging (SLR/LLR), Global Navigation Satellite Systems (GNSS) and ring laser gyroscopes.