The objective of the U.S.-German GRACE satellite mission (Gravity Recovery and Climate Experiment) is to map the global gravity field with unprecedented accuracy. GRACE is a twin satellite configuration based on CHAMP heritage, which was launched on March 17, 2002 into an almost circular, near-polar orbit (inclination 89.0°) with an initial altitude of 500 km.
Both satellites are equipped with the state-of-the-art BlackJack GPS flight receivers for precise orbit determination. In addition the receivers have the capability to perform GPS radio occultation measurements. First 120 of these measurements aboard the GRACE-B satellite were performed during 25 h on July 28 and 29, 2004. Two additional activation periods were: Dec. 2-8, 2004 and Sept. 23-30, 2005. GRACE-A occultation measurements were activated on Jan. 12, 2006, 14:00 UTC until Feb. 21. The data were analyzed in parallel with CHAMP in near-real time. Occultations on GRACE-A were continuously activated in May 2006. Data products are provided by GFZ in near-real time for the use to improve global weather forecasts.
Together with CHAMP, COSMIC and Metop, the GRACE occultation data contribute to the improvement of the GPS radio occultation technique for precise atmospheric sounding on global scale and provide valuable data for various applications in atmospheric/climate research.
BEYERLE, G., T. Schmidt, G. Michalak, S. Heise, J. Wickert, and Ch. Reigber: "GPS radio occultation with GRACE: Atmospheric Profiling utilizing the zero difference technique", Geophys. Res. Lett., 32, L13806, doi:10.1029/2005GL023109, 2005.
WICKERT, J., G. Beyerle, R. König, S. Heise, L. Grunwaldt, G. Michalak, Ch. Reigber, T. Schmidt: "GPS radio occultation with CHAMP and GRACE: A first look at a new and promising satellite configuration for global atmospheric sounding", Annales Geophysicae,Vol. 23, 653-658, 2005.
WICKERT, J., T. Schmidt, G. Beyerle, G. Michalak, R. Koenig, S. Heise, and C. Reigber, GPS radio occultation with CHAMP and GRACE: Recent results, in "Occultations for Probing Atmosphere and Climate", edited by U. Foelsche, G. Kirchengast, and A. K. Steiner, Springer Verlag, ISBN 3-540-34116-1, pp 3-16, 2006.
WICKERT, J., Michalak, G., Schmidt, T., Beyerle, G., Cheng, C.Z., Healy, S.B., Heise, S., Huang, C.Y., Jakowski, N., Köhler, W., Mayer, C., Offiler, D., Ozawa, E., Pave-lyev, A.G., Rothacher, M., Tapley, B., Arras, C., 2008: GPS radio occultation: Results from CHAMP, GRACE and FORMOSAT-3/COSMIC. Terr. Atmos. and Oceanic Sci., in print, 2008.