GRGS > Research > Subjects > The Earth's Rotation and Reference Systems

Bureau des longitudes Centre national d’études spatiales Institut national de l'information géographique et forestière - Laboratoire LAREG Observatoire de Paris Institut national des sciences de l'Univers Observatoire de la Côte d'Azur Service Hydrographique et Océanographique de la Marine Observatoire Midi-Pyrénées Université de la Polynésie Française Ecole Supérieure des Géomètres et Topographes - Conservatoire national des arts et métiers Ecole et Observatoire des Sciences de la Terre

The Earth's Rotation and Reference Systems

A reference frame is needed to compute coordinates on the Earth's surface. The International Terrestrial Reference Frame (ITRF) is calculated by the team LAREG / GRGS, within thethe IERS (International Earth Rotation and Reference Systems Service). It consists of a set of coordinates of some reference points distributed over the globe, including positions and velocities. Because of the availability of new monitoring stations and new data, and improvements in geodesic data analysis, It is regularly updated. The most recent tables are therefore more accurate. Its development requires continual research.

ITRF2008 Velocity Fields

ITRF2008 Velocity Fields

The definition of the reference frame, its origin, scale and orientation, should be as much accurate as possible following the specifications established by the International Terrestrial Reference System (ITRS). In addition, the International Terrestrial reference frame must be consistent with other IERS products, namely the continual estimates of the Earth’s rotation in space (i.e. the rotation of the terrestrial reference frame in space) and the celestial reference frame (ICRF). These reference frames are obtained by combining different estimations of tracking station positions obtained through different space geodesy techniques.

Research is also conducted within the GRGS on the combination of space geodetic measurements in order to estimate terrestrial reference frames and Earth orientation parameters (EOP). This research has been ongoing since 2006 as part of the thesis work of A. Pollet, in collaboration with SYRTE (Observatoire de Paris), which is in charge of operational production of these combined solutions. The main objective of current research is to ensure optimal referencing of solutions of station positions done weekly and, thus, of simultaneously estimated EOP. In particular, tests are underway to take into account local connections between instruments localised with the same satellites and the same techniques, the zenith tropospheric delays common to radio-electric techniques, and multi-technique satellites.

At the Observatoire de Paris, the EOP series obtained by the combination of GINS and DYNAMO is of great interest because of their increased temporal resolution: these series enable us to explore a range of frequencies that are still poorly understood, and they are interpreted in light of atmospheric, oceanic and hydrological transport models.