The Global Geodetic Observing System and Galileo
Rothacher, M.¹; Neilan, R.²; Plag, H.P.^3
1GFZ; ²JPL; ³University of Nevada

The Global Geodetic Observing System (GGOS) was established by the International Association of Geodesy (IAG) in July 2003. In April 2004 the IAG, represented by GGOS, became a participating organization of the Group on Earth Observation (GEO) and in May 2006 GGOS was accepted as a member of the Integrated Global Observation Strategy Partnership (IGOS-P). GGOS is the contribution of geodesy to the Global Earth Observation System of Systems (GEOSS). It provides the metrological basis and the reference systems and frames, which are crucial for Earth observing systems. GGOS is built on the IAG Services (IGS, IVS, ILRS, IDS, IERS, IGFS, etc.) and the products they derive on an operational basis for Earth monitoring, making use of space- and ground-based geodetic techniques such as Very Long Baseline Interferometry (VLBI), Satellite and Lunar Laser Ranging (SLR/LLR), Global Navigation Satellite Systems (GNSS), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), altimetry, InSAR (Interferometric Synthetic Aperture Radar) and gravity satellite missions, gravimetry, etc. All these observation techniques are considered integral parts of GGOS, allowing the monitoring of the Earth's shape and deformation (including water surface), the Earth's orientation and rotation, and the Earth's gravity field and its temporal variations with an unprecedented accuracy. The observed quantities give direct evidence of many global processes that have a crucial impact on human society such as earthquakes, volcanism, floods, sea level change, climate change, ground water redistribution, mass balance of the polar ice sheets, etc. GGOS relies on the observing systems and analysis capabilities already in place in the IAG Services and envisions the continued development of innovative technologies, methods and models to improve our understanding of global change processes and to work towards reliable predictions of future trends. GGOS provides a framework that ranges from the acquisition, transfer and processing of a tremendous amount of observational data to its consistent integration and assimilation into complex numerical models of the Earth system (including solid Earth, oceans, atmosphere, hydrosphere, cryosphere and the interactions thereof). This is being achieved by an international effort and a close, multidisciplinary cooperation with groups working in related fields such as geodynamics, geophysics, oceanography, hydrology, glaciology, meteorology, and climatology. The GNSS, i.e., GPS, GLONASS, and in the future GALILEO and other systems contribute with an astounding diversity to the above mentioned activities. This presentation will introduce GGOS and its essential contributions to an integrated Earth monitoring system. Special emphasis will be put on the crucial role that the GNSS (and especially GALILEO) play in the framework of GGOS.