Launched on March 17, 2002, for the first time ever the GRACE (Gravity Recovery And Climate Experiment) satellite mission allows the determination of global mass variations on (and near) the Earth's surface from changes in the gravitational pull. The underlying measurement principle is as simple as stunning; it is based on the fact that the redistribution of masses maps in changes of the terrestrial gravity field. The spatio-temporal variations of the Earth's gravitational attraction are sensed by a test mass in space.
In case of GRACE, the test mass is a combination of two satellites; the spacecraft are 220 kilometers apart and orbit Earth at an altitude of 450 kilometers. The non-uniform gravitational pull causes the satellites to be accelerated differently. Consequently, the time-variable distance between the spacecraft is a measure for both the structure and the temporal evolution of the Earth's gravity field.
GRACE-related research at the IWF includes studies on secular as well as seasonal mass variations. The investigations have a special focus on the ice-covered regions of the Earth (e.g., Greenland and Antarctica) and large-scale river basins (e.g., Amazon Basin and Nile Basin).
Further information on GRACE is found at the University of Texas at Austin.