R: Practical salinity from electrical conductivity, temperature...

swSCTp {oce} | R Documentation

## Practical salinity from electrical conductivity, temperature and pressure

### Description

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 `eos` is `"unesco"`, then salinity is calculated using the UNESCO algorithm described by Fofonoff and Millard (1983) as in reference 1. Second, if `eos` is `"gsw"`, then the Gibbs-SeaWater formulation is used, via `gsw::gsw_SP_from_C()` 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).

### Usage

    swSCTp(
      conductivity,
      temperature = NULL,
      pressure = NULL,
      conductivityUnit,
      eos = getOption("oceEOS", default = "gsw")
    )

### Arguments

`conductivity` | a measure of conductivity (see also `conductivityUnit`) or an `oce` object holding hydrographic information. In the second case, all the other arguments to `swSCTp` are ignored.
`temperature` | in-situ temperature (degC), defined on the ITS-90 scale; see “Temperature units” in the documentation for `swRho()`.
`pressure` | pressure (dbar).
`conductivityUnit` | string indicating the unit used for conductivity. This may be `"ratio"` or `""` (meaning conductivity ratio), `"mS/cm"` or `"S/m"`. Note that the ratio mode assumes that measured conductivity has been divided by the standard conductivity of 4.2914 S/m.
`eos` | equation of state, either `"unesco"` or `"gsw"`.#'

### Value

Practical Salinity.

### Author(s)

Dan Kelley

### References

1. 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.

2. 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.

3. `gsw_from_SP` online documentation, available at `http://www.teos-10.org/pubs/gsw/html/gsw_C_from_SP.html`

### See Also

For thermal (as opposed to electrical) conductivity, see `swThermalConductivity()`. For computation of electrical conductivity from salinity, see `swCSTp()`.

Other functions that calculate seawater properties: `T68fromT90()`, `T90fromT48()`, `T90fromT68()`, `swAbsoluteSalinity()`, `swAlphaOverBeta()`, `swAlpha()`, `swBeta()`, `swCSTp()`, `swConservativeTemperature()`, `swDepth()`, `swDynamicHeight()`, `swLapseRate()`, `swN2()`, `swPressure()`, `swRho()`, `swRrho()`, `swSTrho()`, `swSigma0()`, `swSigma1()`, `swSigma2()`, `swSigma3()`, `swSigma4()`, `swSigmaTheta()`, `swSigmaT()`, `swSigma()`, `swSoundAbsorption()`, `swSoundSpeed()`, `swSpecificHeat()`, `swSpice()`, `swTFreeze()`, `swTSrho()`, `swThermalConductivity()`, `swTheta()`, `swViscosity()`, `swZ()`

### Examples

    # 1. Demonstrate agreement with test value in UNESCO documents
    swSCTp(1, T90fromT68(15), 0, eos="unesco") # expect 35
    # 2. Demonstrate agreement of gsw and unesco, S>2 case
    swSCTp(1, T90fromT68(15), 0, eos="gsw") # again, expect 35
    # 3. Demonstrate close values even in very brackish water
    swSCTp(0.02, 10, 100, eos="gsw")    # 0.6013981
    swSCTp(0.02, 10, 100, eos="unesco") # 0.6011721

[Package oce version 1.2-0 Index]