Global Geodetic Observing System, 2009
Meeting the Requirements of a Global Society on a Changing Planet in 2020

The Global Geodetic Observing System (GGOS) has been established by the Int- national Association of Geodesy (IAG) in order to integrate the three fundamental areas of geodesy, so as to monitor geodetic parameters and their temporal varia- ?9 tions, in a global reference frame with a target relative accuracy of 10 or b- ter. These areas, often called ?pillars?, deal with the determination and evolution of (a) the Earth?s geometry (topography, bathymetry, ice surface, sea level), (b) the Earth?s rotation and orientation (polar motion, rotation rate, nutation, etc. ), and (c) the Earth?s gravity eld (gravity, geoid). Therefore, Earth Observation on a global scale is at the heart of GGOS?s activities, which contributes to Global Change - search through the monitoring, as well as the modeling, of dynamic Earth processes such as, for example, mass and angular momentum exchanges, mass transport and ocean circulation, and changes in sea, land and ice surfaces. To achieve such an - bitious goal, GGOS relies on an integrated network of current and future terrestrial, airborne and satellite systems and technologies. These include: various positioning, navigation, remote sensing and dedicated gravity and altimetry satellite missions; global ground networks of VLBI, SLR, DORIS, GNSS and absolute and relative gravity stations; and airborne gravity, mapping and remote sensing systems.

The goals, achievements, and tools of modern geodesy.- Understanding a dynamic planet: Earth science requirements for geodesy.- Maintaining a modern society.- Earth observation: Serving the needs of an increasingly global society.- Geodesy: Foundation for exploring the planets, the solar system and beyond.- Integrated scientific and societal user requirements and functional specifications for the GGOS.- The future geodetic reference frame.- The future Global Geodetic Observing System.- Towards GGOS in 2020.- Recommendations.