Applications of Geodesy to Geodynamics: 2. Rotation of the Earth and Polar Motion

Studies of the rotation of the earth and of polar motion have both interdisciplinary and global aspects, involving astronomy, geodesy and geophysics, and even cosmology, in regard to the definition of the inertial reference system. Of concern to us is the establishment of the reference system on a plastic earth, the reference in space, theoretical understanding or at least mathematical modeling of earth rotation and polar motion, the various techniques (optical versus radio; satellites versus distant references), data collection and measurement services and user requirements, and maybe most important, the introduction of new techniques with preservation of continuity in the existing services. The navigation of space probes requires accuracies of 1 to 2 ms in Universal Time and 0.02″ in polar motion, while other users have needs for time and polar motion data with the best available accuracy. Future investigations involving more and increasingly precise data will be used to establish the time span over which the data may be reliably averaged.