Nistad/Westfeld: Fusion of Measured and Synthetic Sound Speed Profiles . 
above. The following is a synthesis of work conducted at the Federal Maritime 
and Hydrographic Agency (Bundesamt für Seeschifffahrt und Hydrographie, 
BSH) to combine synthetic with measured sound speed profile. More detailed 
information is available in Nistad and Westfeld (2022). 
2 Material and Method 
The BSH vessel VWFS Deneb was newly fitted with an AML Oceanographic 
MVP-30 underway profiling system (Fig. 1), which was used to collect a high 
number of sound speed profiles during three multibeam bathymetry surveys, 
which are representative of survey conditions in the southwestern Baltic Sea. 
Fig. 1: The BSH survey vessel VWFS Deneb (left) and the newly installed (June 2020) 
AML Oceanographic MVP-30 underway profiling system (right) 
This high number of profiles, together with the depth measurement data, was 
used to generate the most accurate portrayal possible of the bottom topography. 
This accurate bathymetric model would then serve as reference for statistically 
meaningful comparisons between measured and synthetic profiles. 
BSHcmod is an operational baroclinic regional forecast model operated by 
BSH consisting of two two-way nested grids covering the entire North Sea and 
Baltic Sea. The model version used in this work has a horizontal resolution of 
half a nautical mile (approx. 900 m) and a vertical resolution of approx. 4 m. At 
each node of the model, hourly forecasts of temperature and salinity are availa- 
ble. Synthetic sound speed profiles were derived from BSHcmod using the de- 
pendencies on temperature, salinity and pressure on depth for every available 
node location and time covering the spatial and temporal extent of the survey 
datasets. 
A spatiotemporal interpolation routine from Roemer et al. (2017) was used 
to generate a synthetic sound speed profile at any chosen location and time as 
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