Science rationale of the Global Geodetic Observing System (GGOS)

Geodesy is the science of measuring and mapping the Earth including the associated variations with time. The Global Geodetic Observing System (GGOS) as the "flagship" of the International Association of Geodesy (lAG) aims at the coordination and integration of the corresponding observations in order to generate a uniform set of geodetic parameters for monitoring the phenomena and processes in the System Earth. Coordination means to bring the different geodetic observing techniques and analysis methods together for a consistent performance. The same standards, conventions, models and parameters have to be used in the reduction of observations and in the data analysis for producing compatible results in identical reference systems. Integration implies the inclusion of all relevant information for parameter estimation. The elements of the System Earth are transmitting a variety of signals observable by geodetic techniques. They all have to be considered in a combined analysis. This comprises in particular the integration of geometric and gravimetric data, and the common estimation of all the necessary parameters representing the solid Earth, the hydrosphere (including oceans, ice-caps, continental water), and the atmosphere. Geometric parameters describe primarily the shape of the Earth and its deformation; the gravimetric parameters are functions of the Earth's mass distribution. Considering these facts, the scientific rationale of GGOS is focussing on the central theme "Global deformation and mass exchange in the System Earth".