Development of Geoid Modelling at IfE
The Institut für Erdmessung (IfE) was involved in high-resolution and high-precision gravity field modelling since about 1970. Starting with the local test network Westharz (Torge 1977), significant progress was made in regional and global gravity field modelling within the framework of a collaborative research center project (SFB 149, Geodetic and remote sensing methods onshore and offshore) funded from 1975-1985 by the German Research Foundation DFG (e.g., Torge et al. 1984). From this project, the gravimetric quasigeoid EGG1 (European Gravimetric Geoid 1) for Europe and surrounding marine areas (Torge et al. 1982) as well as the corresponding astrogravimetric solution for Europe (Brennecke et al. 1983) evolved. The accuracies of these models were at the dm level. The transition to accuracies at the cm level was demonstrated successfully for the first time in a local test network near Hannover using high-resolution point gravity and terrain data in combination with a global geopotential model (Denker und Wenzel 1987). Corresponding computations with the spectral combination technique and least-squares collocation were then extended to Northern Germany (Denker 1988), the old West German states (Denker 1989) and finally to entire Europe (e.g., quasigeoid model EGG97, Denker und Torge 1998). Further details on the development and the respective status of geoid modelling in Europe can be found in publications in the German "Zeitschrift für Vermessungswesen" by Torge et al. (1983), Torge and Denker (1991), Denker (1996) as well as Torge and Denker (1999). Furthermore, the gravity field modelling studies at the Institut für Erdmessung (IfE) lead to the habilitation thesis from Wenzel (1985) and the dissertations from Weber (1984), Bäumker (1984), Denker (1988), Bašic (1989), Grote (1996), Behrend (1999) and Roland (2005).
The European geoid and quasigeoid computations were carried out at IfE from 1990 to 2003 as the computing center of the IAG (International Association of Geodesy) geoid sub-commission for Europe. Since 2003, the efforts are continued within an IAG commision project, and a complete update is planned until 2007 (e.g., see Denker et al. 2005). The "European Gravity and Geoid Project (EGGP)" proved that significant accuracy improvements are possible in central Europe through the use of updated gravity field data sets and GRACE geopotential models (Denker, 2006). Moreover, the gravity field data sets from the European Geoid Project are also utilized in connection with the validation and calibration of the satellite gravity field missions CHAMP, GRACE und GOCE (e.g., see Denker 2003, Roland 2005).
Besides the gravimetric geoid and quasigeoid computations, also combined solutions were developed utilizing GPS and levelling data (Denker 1998, Denker et al. 2000). A particular example is the combined quasigeoid model for Germany (German Combined (Quasi)Geoid 2005, GCG2005; Liebsch et al. 2006) which resulted from two independent computation methods applied within a cooperation project of the "Bundesamt für Kartographie und Geodäsie" (BKG) in Frankfurt/Main and the "Institut für Erdmessung" (IfE). Furthermore, a number of local and regional gravity field models (especially geoid) were developed in cooperation with scientific and commercial institutions, e.g., computations for Poland, Hungary, the former GUS states, selected countries in South America and Arabia, as well as a cooperation with Japanese colleagues (Kuroishi und Denker 2001).