Goethe-Universität

Hydrologie

Time-variable gravity and surface mass processes (TIVAGAM):

Validation, Processing and First Application of New Satellite Gravity Data

In March 2002, the GRACE satellite mission (Gravity Recovery and Climate Experiment) was launched as aUS– German joint partnership. GRACE will be able to map the Earth's gravity field by making accurate measurements of the distance between two satellites orbiting the Earth in an altitude of 500 kilometres, using GPS and a microwave ranging system. It will provide scientists from all over the world with an efficient way to map the Earth's static and dynamic gravity field with unprecedented accuracy. The results from this mission will yield crucial information about the distribution and flow of mass within the Earth and its surroundings. The gravity variations that GRACE will study include changes due to surface and deep currents in the ocean, runoff and ground water storage on land masses, exchanges between ice sheets or glaciers and the oceans, and variations of mass within the Earth.

Within the framework of TIVAGAM, the hydrological component of gravity variations will be investigated. Using geophysical reduction models to separate the GRACE gravity signal, continental water storage changes can be identified on a monthly time scale.

The goal of this project is to support the determination of mass anomalies derived from satellite gravity data by providing independent information on the variations of terrestrial water storage. Using the WaterGAP Global Hydrological Model (WGHM), continental water storages are calculated on a global scale with high temporal resolution and thus contribute to quantify aliasing effects and improve de-aliasing methods necessary for processing the satellite’s gravity signal.Short-period mass fluctuations on the sub-monthly scale influence the GRACE signal and need to be eliminated to reduce monthly errors.

Results from both the hydrological and the gravity approach are used to compare, evaluate and calibrate the different applied models and methods. Generating global-scale hydrological information with a high temporal and spatial resolution will contribute to achieve a global geodetic-geodynamic observation system.