The German Research Centre for Geosciences GFZ and the GRACE satellite missions

The German Research Centre for Geosciences GFZ – Germany's national research lab focusing on the solid Earth – is developing solutions to major societal challenges for preserving planet Earth as a safe place to live. These challenges are inextricably linked to the global water balance and to changing water availability. 

The GRACE (Gravity Recovery and ClimateIn contrast to weather, which refers to daily or very short-term events, climate refers to an average condition in the atmosphere over a longer period of 30 to 40 years. All processes such as average temperature, precipitation, wind direction, wind s... Experiment) and GRACE-FO (Follow-On) satellite missions document large-scale mass changes in the Earth system that cannot be detected by other remote sensing satellites. The aim of the missions is to permanently observe the effects of the diverse and complex feedbacks of human activity on the global water cycle, sea-level rise and the climate system. The GFZ has been involved in the GRACE satellite missions for more than 20 years together with its German and American partners.

Due to the huge scientific success of the first GRACE mission (2002-2016), the German Research Centre for Geosciences (GFZ) has been planning the follow-up mission GRACE-FO together with JPL/NASA since 2009 and has helped to secure the financing of the German mission shares. In addition to launch rocket, mission operations and scientific evaluation, German funding also covered the construction of the optical components of a laser ranging interferometer (LRI) as a technology demonstrator for future gravity field missions in cooperation with the Max Planck Institute for Gravitational Physics in Hanover.

For the third mission, GRACE-C, which is to continue the time series of GRACE-FO from 2028 onwards on the basis of LRI observations, the GFZ carried out the planning phases together with DLR and in close coordination with NASA, and once more secured the necessary funding for the German mission shares (similar to GRACE-FO) in November 2022.

After reaching orbit with a suitable launch vehicle, the operation of the two satellites and their instruments must be continuously monitored and controlled. For this purpose, the GFZ has commissioned the German Space Operation Center (GSOC) of the German Aerospace Center (DLR) for GRACE-FO. The tasks are manifold and include sending the necessary commands to the satellites and instruments, receiving the data, pre-processing the telemetry data received, and transferring this data via the Raw Data Center (RDC) at GSOC to the Science Data System (SDS) for further processing and the generation of scientific products. The GFZ is part of the SDS together with NASA's Jet Propulsion Laboratory in Pasdena (California/USA) and the Center for Space Research at the University of Austin (Texas/USA). However, the antennas used by GSOC in Weilheim (Bavaria) and Neustrelitz (Mecklenburg-Western Pomerania) only have contact with the two satellites about every 12 hours. Those limited contact opportunities are the reason why the GFZ operates the primary receiving station for GRACE-FO (and later for GRACE-C) in Ny-Ålesund on Spitsbergen. Due to its location near the North pole (78° 55' North), the GFZ station has contact with the satellites virtually at every orbit, i.e. about every 95 minutes, which means that the data is available much more rapidly for further analysis, and the project team can react much quicker to any problems on board the satellites in case of an emergency.

The monthly Level-2 gravity field products of the SDS are available in the form of spherical function coefficients, which are quite difficult to process by non-experts for further analyses. For this reason, the GFZ generates fully corrected monthly Level-3 gridded data for the land areas, the oceans, and the two large ice sheets in Greenland and Antarctica in the Gravity Information Service (GravIS) together with the Alfred Wegener Institute in Bremerhaven and the Technical University of Dresden.

To distribute data to the international user community, the GFZ also operates the Information System and Data System (ISDC), where all Level-1B (corrected instrument data and correction models) to Level-3 products of GRACE and GRACE-FO can be obtained free of charge. The ISDC complements the visualisation options provided in GravIS.