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Abstract

In the year 2021 a milestone was reached in the absolute gravity research at the Finnish Geospatial Research Institute, when the expansion of the absolute gravity network in Finland was completed. The stations in the network are co-located with the FinnRef permanent GNSS network. This enables studying long-term gravity change, including the Fennoscandian Post-glacial rebound phenomenon, in parallel with deformation monitoring and monitoring of the 3D reference frame. The first absolute gravity measurements in Finland were made in the 1970s and 1980s in Metsähovi, Vaasa and Sodankylä. When the FinnRef network was built in the 1990s, facilities for absolute gravity measurements were established at 5 co-located sites. In 2012-2018 the FinnRef network was modernized and gradually expanded. At the same time, more absolute gravity facilities were built, raising the number of absolute gravity stations from 8 to 19. The latest absolute gravity station added was the Finnström station in the Åland Archipelago, closing a major gap in the Nordic absolute gravity site coverage.The FinnRef permanent GNSS network now consists of 47 stations. The subset of 19 stations contains facilities for absolute gravity measurements. These stations, homogeneously distributed over the country, are repeatedly measured in a 3-year cycle with the FG5X-221 absolute gravimeter, which is the national standard of free-fall acceleration in Finland. The stations also form the zero-order absolute gravity network, to which the renewed First Order Gravity Net (FOGN) is tied. We will describe the absolute gravity stations and the measurements made at them.