Improving terrain navigation by concurrent tidal and sound speed error estimation

Terrain navigation in the presence of an unknown tide level has been demonstrated earlier, where both horizontal position and depth errors of a nominal navigation solution can be estimated concurrently. Accurate bathymetric measurements based on acoustic sensors also rely on knowing the sound speed near the sensor and in the water column between the sensor and the sea floor. This is important for vessels operating far from the sea floor, but also for underwater vehicles operating near the sea floor with side-looking bathymetric systems. To enable high performance terrain navigation in those scenarios, the sound speed error must also be considered. This paper proposes three different modifications to a 2D point mass filter to enable concurrent compensation for tide and sound speed error. Simulations so far indicate a great improvement compared to using a regular 2D point mass filter.