Marine Gravity Measurements for Geoid Determination and Height System Unification in the FAMOS Project

The main component of the FAMOS (Finalising Surveys for the Baltic Motorways of the Sea) project is to finalise hydrographic surveying in those areas of the Baltic Sea that are of interest for commercial shipping. In the Harmonising vertical datum activity of this project, the main goal is to improve the geoid over the Baltic Sea area, to provide an important basis for future offshore navigation. This is also crucial for the on-going efforts of the the Chart Datum Working Group (CDWG) of the Baltic Sea Hydrographic Commission (BSHC) to introduce the European Vertical Reference System (EVRS) as chart datum in the Baltic Sea. To reach the goal of an improved geoid model, new marine gravity data will be collected in connection with the hydrographic surveying, both to check existing gravity data and to fill in empty areas. The activity also includes computation of the geoid model, possibly using alternative methods in order to find a methodology suitable for the area in question. Another important but difficult part is validation. According to the plan, the validated FAMOS geoid model will be ready by 2020. The main purpose of this presentation is to describe on-going and planned activities in the Harmonising vertical datum activity of the FAMOS project.