Towards a Roadmap for Future Satellite Gravity Missions September 30 - October 2, 2009, Graz, Austria

Rationale: The CHAMP and GRACE satellite missions, in orbit since 2000 and 2002, respectively, have significantly improved the spatial resolution and precision of our gravity field models, pushing our knowledge of the static gravity field to centimeter level accuracy in geoid determination. The recently launched European GOCE mission will provide further improvements in accuracy and spatial resolution of the static part of the gravity field. The integration of various satellite missions with geometric techniques such as GPS, SLR and DORIS (monitoring, a.o., changes in the rotation and figure of the Earth), have created new opportunities for the study of mass transport in the Earth system in a globally consistent way. The GRACE mission monitors changes in Earth's gravity field and provides unprecedented insight in water storage changes at sub-continental scales in land water storage, ice sheets and oceans. Oceanographic applications illustrate the unique way in which the combined geodetic observations provide accurate and quantitative constraints on the ocean mass budget, tidal dissipation, near-surface ocean flow and its variability, and large-scale ocean mass variations. The observations are invaluable for understanding the causes of sea level rise and the dynamics of ocean mass redistribution.

Despite the importance of the gravity missions as part of the global geodetic observing system and, in particular, the global water cycle observing system, we are facing a serious challenge in maintaining the observations at current level or increasing spatial and temporal resolution to a level required by many geoscientific applications. GRACE is estimated to cease operation about 2012. If at that time no follow-on mission is launched, the gap in gravity observation would significantly hamper exploitation of the gravity observations for climate studies and the detection of climate change impacts on the global water cycle. It is therefore of paramount importance to come to a global agreement on how sufficient semi-operational satellite gravity missions can be ensured and necessary developments towards increase accuracy, spatial and temporal resolution, and lower latency of products can be facilitated. In parallel, a medium to long-term perspective has to be developed to ensure a continuous and sustainable monitoring of mass transport in the Earth system by means of future gravity satellite missions.