How is the actual status of our planet Earth, its interior, on the surface and in the Earth’s atmosphere? What are the driving forces for the global change processes? Can permanent monitoring lead to a possible prediction of future global changes and, if yes, how? Questions for our home planet, which find the answer in a nearly unlimited bulk of data placed at disposal by artificial satellites of different kind and layout, equipped with special sensors for different tasks. They outline a global picture of our planet with an, up to now, unknown resolution which allows for the investigation of detailed structures. The task remains how to de-correlate this global picture and to pick out the individual items required for the understanding of the basic physical processes.

For example, the precise knowledge of the Earth's gravity field and its temporal changes contributes to the detection of the mechanisms leading to the building of the Earth's crust, the evolution of the green house effect and the realization of the ocean and air currents. The determination of precise station coordinates via GPS and laser leads to the definition of a temporal changing velocity field which enables the investigation of the underlying driving forces and the energy transport in the Earth's crust, an important prerequisite for an eventual future earthquake prediction. A precise calibration and validation of altimeter data are a fundamental prerequisite for reliable predictions concerning the sea level rise. The path delays of GNSS electromagnetic waves or a precise analysis of satellite in orbit accelerations allow atmospheric sounding and thus assist the modelling of the "space weather" which is determined by the Sun activity and the magnetic field of the Earth.

But, also the Earth orbiting satellites interact, via the gravity field, with the forces they should ask for. Thus, the connection of the satellite reference frames (precise knowledge of the satellite orbits) to the terrestrial frame is of utmost importance. "Geometrical" laser and microwave measurements are not affected by the interplay of forces, they are the only means to fulfill this task.