Issue n. 2, December 2004 [pp. 88-93]
Status of the European Gravity and Geoid Project EGGP
The latest high-resolution European geoid and quasigeoid models (EGG97) were computed at the Institut für Erdmessung (IfE), University of Hanno-ver, acting since 1990 as the computing center of the International Association of Geodesy (IAG) Sub-commission for the European Geoid (predecessor of the EGGP), for details cf. Denker and Torge (1998). EGG97 is based on high-resolution gravity and terrain data in connection with the global geopotential model EGM96. The evaluation of EGG97 by GPS/levelling data revealed the existence of long wavelength errors at the level of 0.1 to 1 ppm, while the agreement over distances up to about 100 km is at the level of 0.01 m in many areas with a good quality and coverage of the input data (Denker and Torge, 1998; Denker, 1998). Since the development of EGG97, significant new or improved data sets have become available, including strongly improved global geopotential models from CHAMP and GRACE, new national and global terrain data sets, new or updated gravity data sets, improved altimetric results, as well as new GPS/levelling campaigns. Furthermore, also the combination of ship and altimetric data has been refined, and new gravity field modelling techniques, e.g., wavelet techniques, fast collocation, etc., have become operational. Considering all these advancements, a complete re-computation of the European geoid/quasi geoid is appropriate and promises significantly improved accuracies, especially at long wavelengths. Therefore, after the IUGG General Assembly in Sapporo in 2003, it was decided to support this task in the form of an IAG Commission 2 Project, named CP2.1 and entitled “European Gravity and Geoid Project EGGP”. The project is reporting to Sub-commission 2.4 and has strong connections to the International Gravity Field Service (IGFS), with its centers Bureau Gravimétrique International (BGI), Internation-al Geoid Service (IGeS), National Geospatial-Intelligence Agency (NGA), and GeoForschungsZentrum Potsdam (GFZ), as well as to several other IAG bodies, e.g., EUREF. The EGGP is running within the 4-year period from 2003 to 2007 until the next IUGG General Assembly. The project is organised by a steering committee (H. Denker (Chair), J.-P. Barriot, R. Barzaghi, R. Forsberg, J. Ihde, A. Kenyeres, U. Marti, I.N. Tziavos) and has about 50 national delegates (project members) from most of the countries in Europe. The EGGP terms of reference can be found in EGGP (2003). This contribution gives an overview on the general computation strategy and on the progress in the collection of gravity data, terrain data, and global geopotential models from the new space missions CHAMP and GRACE. First updated geoid/quasigeoid solutions are presented based on the new global geopotential models from CHAMP and GRACE. Moreover, results from an improved terrestrial gravity data set, including reprocessed ship gravity and new altimetric anomalies, are presented.