Gravity Measurements along Commercial Ferry Lines in the Baltic Sea and Their Use for Geodetic Purposes

Abstract

In 2017 and 2018 GFZ performed two gravimetry campaigns on commercial ferries in the Baltic Sea. The nature of such “non-dedicated” campaigns is different from “dedicated” campaigns that are performed on research vessels with tracks planned according to gravity measurement needs. The non-dedicated campaigns use non-survey vessels or survey vessels running for other purposes such as hydrographic measurements, which may require additional corrections. To assess the usefulness of non-dedicated campaigns, we analysed gravity measurements collected on two commercial ferries as part of the EU funded FAMOS project. Besides the typical marine gravimetry corrections, we also investigated the corrections for the vertical accelerations due to the ship’s movement and the dynamical effect due to the cross-coupling between horizontal and vertical acceleration components. Taking the latter two corrections into account partly leads to slight improvements, but our results also demonstrate that the standard processing without the two corrections, as used in most of the dedicated campaigns, already delivers good quality end products that fulfil the requirements of a typical marine gravimetry survey with an uncertainty of about 1 mGal. Our findings suggest that gravimetry campaigns on commercial ferries can be used to complement dedicated marine gravimetry campaigns and contribute to geodetic purposes.

Keywords:

• Baltic Sea
• Chekan-AM
• FAMOS project
• ferry gravimetry
• kinematic vertical acceleration
• Shipborne gravimetry

Acknowledgements

The two ferry campaigns were performed within the Finalising Surveys for the Baltic Motorways of the Sea (FAMOS) project that was supported by the European Commission within the Connecting Europe Facility (CEF) Transport Sector under the Grants No. INEA/CEF/TRAN/M2014/1027106 and INEA/CEF/TRAN/M2015/1124688. GFZ’s activities in the ferry campaigns as well as the above-mentioned dedicated campaigns were financially supported for 50% from the FAMOS project. The implementation of these ferry campaigns was made possible by the support of Finish Transport Agency (FTA), Maritime Administration of Latvia (MAL) and German Federal Maritime and Hydrographic Agency (BSH). The shipping companies Stena Line Scandinavia AB Göteborg and Finnlines Oyj Helsinki are acknowledged for supporting our project. The crews on the ferry liners are thanked for their help and understanding during the campaigns and for their hospitality onboard. Mirjam Bilker-Koivula and Hannu Ruotsalainen from Finnish Geospatial Research Institute (FGI) are acknowledged for providing the gravity reference in Helsinki, and Jan Müller and Andreas Reinhold from Federal Agency for Cartography and Geodesy (BKG) for providing the gravity reference and gradient measurements in Travemünde. Finally, the two anonymous reviewers and the associate editor are acknowledged for their helpful comments on an earlier version of this manuscript. The final processed dataset (Ince et al. 2020) can be downloaded from GFZ Data Services. http://doi.org/10.5880/GFZ.1.2.2020.001.