Space: LOTSE CHAMP/GRACE

© GRACE-Projektbüro

The joint project LOTSE-CHAMP/GRACE has the overall goal to reprocess aII CHAMP and GRACE gravity, magnetic and radio occultation mission data to derive long, consistent and high-quality time series of static and time variable gravity field models describing the mass distribution and mass variation in the system Earth, atmospheric parameters (e.g., mean global temperatures, tropopause altitudes, humidity) and the state and change in the Earth's outer core and lithospheric magnetic field. These consistent data sets can then be used by the national and international user community as a valuable and complementary source of information for global change analysis such as monitoring of the continental hydrological cycle, polar ice mass or sea level change. climate research and for geological and tectonic studies.

The motivation for the CHAMP and GRACE data reprocessing is driven by various facts:

- CHAMP, launched on July 2002 during high solar activity with an initial altitude of 450 km, has meanwhile reached an extremely low orbit of just 340 km at minimum solar activity which leads to a very high quality of gravity and magnetic data.

- This orbit decay -less pronounced- and the low solar activity also exist for GRACE. In parallel we have gathered and improved our experience with the highly complex GRACE sensor system. But there are still a lot of open questions related to instrument data processing (especially for K-band and accelerometer data) and background modeling (e.g. the de-aliasing of tidal and non-tidal atmospheric and oceanic mass variations).

- For CHAMP and GRACE long time series of up to 8 and 6 years, respectively, of gravity field data are already available, but for GRACE these time series still do not meet the pre-launch simulated baseline and need to be reprocessed with improved observation and background models and processing standards to get a reliable data set to be used for global change analysis and climate research e.g. in the German Special Priority program SPP l257 'Mass Transport and Mass Distribution in the Earth System".

- CHAMP provides currently the only and world-wide unique long-term set of globally distributed GPS radio occultation data, which was started in 2001 and is extended by the GRACE RO measurements since 2006. These data are in use by numerous scientists to derive initial information on climatologically variations of the Earth's atmosphere. There is consensus of the international user community on the need of a consistent and reprocessed GPS RO data set from both satellites.

- The number of CHAMP and GRACE data users is more or less growing exponentially. At GFZ's ISDC (lnformation System and Data Center) we had 400 registrations end of 2003, 670 mid of 2005 (begin of GEOTECHNOLOGIEN 2 program) and today more than 1800. In parallel the number of GRACE publications is growing in a similar way (a -surely still - incomplete list can be found at http://www-app2.gfz-potsdam.de/pbl/op/grace). Both points to the fact that a growing interest in high-precision long time series of CHAMP and GRACE data and products exists.

Consequently, the high level goals of this joint proposal are therefore:

l. Find the reasons for the yet not achieved GRACE baseline gravity field accuracy.
2. Reprocess all CHAMP and GRACE gravity, magnetic and radio occultation mission data to derive long, consistent and high-quality time series of the continental hydrological cycle, polar ice mass and sea level change, atmospheric parameters (e.g. tropopause height, temperature, humidity) and the state and change in the Earth's outer core and lithospheric magnetic field. These consistent data sets can then be used as a valuable and complementary source of information for global change analysis, climate research and for geological and tectonic studies.
3. Derive a high-accuracy static satellite-only gravity field and its seasonal variations to be combined with GOCE real data.
4. Demonstrate the feasibility to derive reliable information on climatological variations of the Earth's atmosphere based on the GPS RO data sets from CHAMP and GRACE.

Co-ordination:
Dr. Frank Flechtner
Global Geomonitoring and Gravity Field
Deutsches GeoForschungsZentrum Potsdam

Partners:
GFZ Potsdam
University Bonn
Technical University Munich
University Potsdam