Calculate salinity from what is actually measured by a CTD, i.e.
conductivity, in-situ temperature and pressure. Often this is done
by the CTD processing software, but sometimes it is helpful to do this
directly, e.g. when there is a concern about mismatches in sensor
response times. Two variants are provided. First, if
"unesco", then salinity is calculated using
the UNESCO algorithm described by Fofonoff and Millard (1983) as in
reference 1. Second, if
"gsw", then the
Gibbs-SeaWater formulation is used, via
in the gsw package. The latter starts with the same formula
as the former, but if this yields a Practical Salinity less than 2,
then the result is instead calculated using
formulae provided by Hill et al. (1986; reference 2), modified to match the
"unesco" value at Practical salinity equal to 2 (reference 3).
swSCTp( conductivity, temperature = NULL, pressure = NULL, conductivityUnit, eos = getOption("oceEOS", default = "gsw") )
a measure of conductivity (see also
in-situ temperature (\(^\circ\)C), defined
on the ITS-90 scale; see “Temperature units” in the documentation for
string indicating the unit used for conductivity.
This may be
equation of state, either
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.
K. Hill, T. Dauphinee, and D. Woods. “The Extension of the Practical Salinity Scale 1978 to Low Salinities.” IEEE Journal of Oceanic Engineering 11, no. 1 (January 1986): 109-12. https://doi.org/10.1109/JOE.1986.1145154.
gsw_from_SP online documentation, available at
Other functions that calculate seawater properties:
# 1. Demonstrate agreement with test value in UNESCO documents swSCTp(1, T90fromT68(15), 0, eos="unesco") # expect 35#>  35# 2. Demonstrate agreement of gsw and unesco, S>2 case swSCTp(1, T90fromT68(15), 0, eos="gsw") # again, expect 35#>  35# 3. Demonstrate close values even in very brackish water swSCTp(0.02, 10, 100, eos="gsw") # 0.6013981#>  0.6013981swSCTp(0.02, 10, 100, eos="unesco") # 0.6011721#>  0.6011721