swSoundAbsorption {oce} | R Documentation

## Seawater sound absorption in dB/m

### Description

Compute the sound absorption of seawater, in dB/m

### Usage

    swSoundAbsorption(frequency, salinity, temperature, pressure, pH = 8,
      formulation = c("fisher-simmons", "francois-garrison"))

### Arguments

`frequency` | The frequency of sound, in Hz.
`salinity` | either practical salinity (in which case `temperature` and `pressure` must be provided) or an `oce` object, in which case `salinity`, `temperature` (in the ITS-90 scale; see next item), etc. are inferred from the object.

`temperature`

in-situ temperature [degC], defined on the ITS-90 scale. This scale is used by GSW-style calculation (as requested by setting `eos="gsw"`), and is the value contained within `ctd` objects (and probably most other objects created with data acquired in the past decade or two). Since the UNESCO-style calculation is based on IPTS-68, the temperature is converted within the present function, using `T68fromT90`.

`pressure` | pressure [dbar]
`pH` | seawater pH
`formulation` | character string indicating the formulation to use, either of `"fischer-simmons"` or `"francois-garrison"`; see “References”.

### Details

Salinity and pH are ignored in this formulation. Several formulae may be found in the literature, and they give results differing by 10 percent, as shown at [3] for example. For this reason, it is likely that more formulations will be added to this function, and entirely possible that the default may change.

### Value

Sound absorption in dB/m.

### Author(s)

Dan Kelley

### References

1. F. H. Fisher and V. P. Simmons, 1977. Sound absorption in sea water. J. Acoust. Soc. Am., 62(3), 558-564.

2. R. E. Francois and G. R. Garrison, 1982. Sound absorption based on ocean measurements. Part II: Boric acid contribution and equation for total absorption. J. Acoust. Soc. Am., 72(6):1879-1890.

3. http://resource.npl.co.uk/acoustics/techguides/seaabsorption/

### See Also

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

### Examples

    ## Fisher & Simmons (1977 table IV) gives 0.52 dB/km for 35 PSU, 5 degC, 500 atm
    ## (4990 dbar of water)a and 10 kHz
    alpha <- swSoundAbsorption(35, 4, 4990, 10e3)

    ## reproduce part of Fig 8 of Francois and Garrison (1982 Fig 8)
    f <- 1e3 * 10^(seq(-1,3,0.1)) # in KHz
    plot(f/1000, 1e3*swSoundAbsorption(f, 35, 10, 0, formulation='fr'),
         xlab=" Freq [kHz]", ylab=" dB/km", type='l', log='xy')
    lines(f/1000, 1e3*swSoundAbsorption(f, 0, 10, 0, formulation='fr'), lty='dashed')
    legend("topleft", lty=c("solid", "dashed"), legend=c("S=35", "S=0"))

[Package oce version 0.9-22 Index]