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], defined on
the ITS-90 scale; see Temperature units in the documentation for
swRho, and the examples below.
pressure
pressure [dbar]
longitude
longitude of observation (only used if eos="gsw"; see
Details).
latitude
latitude of observation (only used if eos="gsw"; see
Details).
eos
equation of state, either "unesco" [1,2] or "gsw"
[3,4].
Value
Sound speed [m/s].
Details
If the first argument is a ctd or section object, then
values for salinity, etc., are extracted from it, and used for the
calculation, and the corresponding arguments to the present function are
ignored.
If eos="unesco", the sound speed is calculated using the formulation
in section 9 of Fofonoff and Millard (1983). If eos="gsw", then the
gsw_sound_speed function from the gsw package
is used.
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.)