The twin satellites of the Gravity Recovery and Climate Experiment (GRACE) were launched on March 17, 2002. With the two satellites orbiting on the same track, the primary mission goal is to map the Earth’s gravity field and its temporal variations with unprecedented accuracy. Furthermore, GRACE provides information on vertical temperature and water vapor distribution of the atmosphere.
The masses within the Earth and on its surface are not homogeneously distributed. Many long- to short-term processes, such as molten rock flows in the Earth´s core and mantle, ice mass loss in the Polar Regions as well as water mass redistribution in the oceans or in large river basins cause permanent mass displacements. Since the force of gravity of an object depends on its mass, this irregular mass distribution causes the inhomogeneous gravity field of our planet. Consequently, regions of slightly stronger gravity will affect the leading GRACE satellite first, pulling it slightly away from the trailing satellite. This is reflected by a small change in the inter-satellite distance. Consequently, by a high-precision tracking of the permanently changing distance, tiny mass variations on ground can be measured and are provided as monthly maps of the Earth´s gravity field which provide new insight into many climatological processes in system Earth.
But as the lifetime of GRACE is limited and only longtime series can give sufficient accuracy for long-term climate trend estimations, a GRACE-FO (Follow-On) mission, again involving significant GFZ contribution, is currently scheduled to be launched by the end of 2016.