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...

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...