Earth Rotation and Its Parameters

Abstract

The Earth is under continuous influence of external attractive forces of the Sun and Moon, as well as an internal coupling between the Earth’s core and mantle and mass movements. This is why its rotation is not uniform. The direction of its rotation vector experiences long-term and periodic changes w.r.t. a space-fixed reference system (precession and nutation), as well as changes w.r.t. the Earth-fixed reference system (polar motion). Fluctuations in the Earth’s rotation speed are known as length of day (LOD) variations. Precession, nutation, polar motion, and length of day are together called Earth orientation parameters (EOP). They are the link between the celestial and terrestrial reference frames, and therefore, crucial in the transformation between them. This paper introduces the reader to the variable Earth rotation and the driving forces acting behind it, as well as the corresponding EOPs and reference frames. It gives a brief historical overview on latitudinal observations, and how they impacted the establishment of the today-known IERS (International Earth Rotation and Reference Systems Service). Furthermore, a description on the currently used techniques for the determination of EOPs is given at the end of this work, continuing with an example of utilizing GNSS observations for the determination of Earth rotation parameters (ERP).