Section 1.2: Earth Observation Satellites

Satellite geodesy stepped into the 21st century with a completely new generation of near-Earth satellites. The individual satellites Champ and GOCE, as well as the tandem satellites of the Grace mission are equipped with highly sensitive instruments that can exactly measure even the smallest accelerations. The GFZ plays a leading role in the construction and operation of these modern marvels of satellite technology. All four of them transmit data continuously, which we archive and process. From them, we first calculate the orbits with high precision, and use them to develop models of the gravitational field in near realtime. For the first time, this has permitted precise and homogeneous measurement of the distribution of masses in the Earth system and of their displacements over short time intervals. Among these mass displacements are factors relevant to the climate such as the water cycle over continents, the melting of polar ice fields and the surface and deep currents within the oceans. In addition, we measure the Earth's magnetic field with Champ.

We also participate in the analysis of data from the European remote sensing satellites ERS-1 and -2, the environmental satellite Envisat as well as a selection of other international satellites. Our main interest are the data and observations from altimetry instrumentation. For this purpose, we maintain the corresponding data archive and processing center for Germany. We calculate from these data, for example, climate related changes in sea level, but also altitude models on land. In addition to the altimetry satellites, we also operate and use a network of tide gauges on coasts, and GPS-buoys on the high seas. These permit us to record long term changes in sea level and to calibrate the satellite measurements.

In addition, we support a series of satellite missions by tracking them. For this purpose, we maintain the Potsdam Laser Tracking System, that is integrated into the global network, and operate in Ny-Ålesund on Svalbard a satellite receiver station. For the Champ mission we developed a laser reflector that has now been reproduced in our workshops for many other satellite missions.