Objectives  Marine gravimetry is a critical method for obtaining high-precision, high-resolution earth gravity field information in the marine areas. For geoid improvement, the absolute reference of the gravity is of particular interest (in contrast to, e.g., exploration geophysics, where relative accuracy, or precision, is sufficient). Therefore, a constant drift behavior of the gravimeter and also the reference readings in the harbor are important for this application.

  Methods  The processing strategy of marine gravimetry in the Baltic Sea is studied. The drift function based on gravity differences at crossover points is used to reduce the influence of the abnormal gravimeter drift and the measurement accuracy reached 0.5 mGal. In 2017, the drift stability of the air-marine gravimeter Chekan-AM is significantly improved after an update. Besides, the real measured gravity gradients instead of the normal gravity gradient (0.308 6 mGal/m) in the harbors are used to calculate the gravity differences between the Chekan-AM sensor and connection points due to their large altitude differences in the campaign URD2017.

  Results  The gravimetry data processing results show that the accuracy of the marine gravimetry onboard the conventional research vessel is 0.2 mGal and that onboard the ferry is 0.6 mGal. The accuracy reaches the aim of sub-mGal in the project of Finalising Surveys for the Baltic Motorways of the Sea (FAMOS) and is even close to the current highest accuracy level of 0.1–0.2 mGal in marine gravimetry. The preliminary results of the construction of the local geoid in the Baltic Sea region are given, which proves that the obtained marine gravity measurement data plays an important role in filling data gaps, verifying old gravity data and improving the accuracy of the regional geoid.

  Conclusions  Our research provides the foundation of marine gravimetry technologies and gravity data sets for establishing a unified geoid for the entire Baltic region in the future.