Speed of Sound in Water Calculator
For a specified temperature, salinity, and pressure/depth, this set of calculators estimates the speed of sound in water. The coefficients in the underlying equations are experimentally determined for a particular set of conditions, so check the Range of validity table to determine the correct calculator to use.
The calculators are described in more depth here, including the equation coefficients, their development history, a discussion of their uncertainty, and the references they were compiled from.
While ROVs and other underwater systems frequently come equipped with depth and temperature sensors, salinity sensors are less common.
Average ocean surface salinity levels are 35‰ (parts per thousand), but can vary by global location and proximity to fresh water inflows. An interactive globe of ocean salinity levels with monthly data can be found here. Salinity also varies by depth, although the specifics of this are less well mapped out across the globe because satellite imagery can only estimate salinity at the surface. Typically there is a salinity reduction of about 1‰ over the first 500m or so.,
For a more general understanding of the salinity of different water types, see the following diagram: