Starting point / motivation
Earth’s gravity field is an important indicator of mass variations within the dynamic system of our planet. Primary sources of these mass redistributions are climate relevant geophysical and anthropogenic processes, such as continental hydrology, Earth’s cryosphere as well as large scale ocean and atmosphere fluctuations.
Some prominent examples include man-made groundwater depletion in northern India, the melting of the Greenland ice sheet or major hydrological events such as the Danube floods in the year 2006. The observation of the time-variable gravity field can therefore contribute to the development of sustainable strategies for reducing the impact of global climate change.
During the last decade, dedicated satellite missions to observe the Earth’s gravity, such as
- the ESA mission GOCE (Gravity field and steady-state Ocean Circulation Explorer), and
- the NASA operated missions CHAMP (CHAllenging Minisatellite Payload) and
- GRACE (Gravity Recovery And Climate Experiment) have been realised.
In the context of climate monitoring, GRACE holds a special status within this group. Due to its unique measurement principle, relying on highly-accurate distance measurements between a leading and a trailing satellite, GRACE is extremely sensitive to mass changes on and above Earth’s surface. Since its launch in 2002 it has enabled a continuous monitoring of the time-variable gravity field, providing an invaluable time series for climate research.
The importance of this mission is underlined by over 3000 related scientific publications and numerous contributions to the IPCC (Inter governmental Panel on Climate Change) assessment report. After over 14 years in orbit, the satellites are close to their end-of-life and are expected to re-enter the atmosphere in late 2017/early 2018.
The successor of the mission, Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), is already in its implementation phase and is due for launch at the end of 2017.
Contents and goals
The primary goal of GRACE-FO is to extend the time series of temporal gravity field solutions, but it will also serve as a technology demonstrator, implementing the first Laser Ranging Interferometer (LRI) between two satellites in orbit.
The aim of the proposed project is to prepare for the handling and processing of the new GRACE-FO instrument data and to continue and improve the time-variable gravity field record.
In addition to pre-processed data products (Level-1B) as available from GRACE, for GRACE-FO the raw observations (Level-1A) will be publicly available for the first time. This will enable a more detailed analysis of the satellites’ instrument, not only providing improved gravity field solutions but also yielding insights for the design of future gravity field missions.
To continue and improve the gravity field time series, it is necessary to meet the challenges of new data, to incorporate new observation types into the gravity field recovery, as well as to enhance processing methodologies of both Level-1A and Level-1B data products.
In summary, a processing chain tailored to the data and requirements of GRACE-FO is envisaged, providing an indispensable continuous highly-accurate data record for climate change research.
Univ. Prof. Dr. Ing. Torsten Mayer-Gürr