Until 1972, astrometry based on a network of optical instruments was the only technique able to monitor the Earth orientation (polar motion, Universal Time and nutation). Since various techniques have shown their capability to give all or a part of these parameters: Doppler observations of navigation satellites, laser ranging to the Moon and to dedicated artificial satellites, Very Long Baseline Interferometry (VLBI) and more recently GPS and DORIS. The different Earth Orientation Parameters (EOP) series obtained by the individual techniques are inhomogeneous in time span, quality, time resolution – which supports the concept of combined solutions taking advantage of the various contributions.
The main task of IERS is the maintenance of both a conventional terrestrial reference system based on observing stations and a conventional celestial reference system based on extragalactic radio sources and also the matrix product allowing the transformation between these two systems which takes into account precession-nutation, polar motion and Earth rotation.
The objective of this paper is to present the evolution, the state of the art and future prospectives concerning the multi-technique EOP combined solution made at IERS/CB.