International Earth Rotation Service - IERS

The research concerns Earth rotation studies using observations derived from space geodesy, such as GPS and DORIS systems, laser ranging to the moon and artificial satellites and very long baseline interferometry (VLBI).

Its scientific activities are primarily linked to conceptual definition of various reference systems, models and parameters connected to geodynamics (precession, nutation, polar motion, variations in the earth's rotation). They are developed in the frame of the International astronomical Union (IAU) within working groups in charge of the preparation of the IAU resolutions, scientific terminology and standard models to be used in the field. Other researches are developed in the field of astronomy and geodynamics in relation to geodesy and geophysics. Firstly, metrology of both terrestrial and celestial reference systems with respect to the Earth orientation and secondly the analyses of geophysical phenomena affecting the earth rotation, external like atmosphere and ocean as well as internal, mantle and the core.

It can be represented as the intersection of the Earth's axis of rotation with a plan tangent to the terrestrial pole. The resulting motion is composed of an annual term, of atmospheric origin superimposed to the Chandler term, which is a free motion. The polhody fits in approximately a 20m square. The uncertainty is smaller than one centimetre.

Example of earth rotation parameters: Polhody or polar motion.