either salinity [PSU] (in which case
temperature and pressure must be provided) or
a ctd object (in which case salinity,
temperature and pressure ar
temperature
in-situ temperature [$^\circ$C]
pressure
pressure [dbar]
Value
Sound speed [m/s].
Details
If the first argument is a ctd object, then salinity,
temperature and pressure values are extracted from it, and used for
the calculation.
The sound speed is calculated using the formulation in section 9 of
Fofonoff and Millard (1983).
References
Fofonoff, P. and R. C. Millard Jr, 1983. Algorithms for
computation of fundamental properties of seawater. Unesco
Technical Papers in Marine Science, 44, 53 pp. (See section
9.)