Compute the sound absorption of seawater, in dB/m

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 (\(^\circ\)C), 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”.

Value

Sound absorption in dB/m.

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 in reference 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.

References

  1. F. H. Fisher and V. P. Simmons, 1977. Sound absorption in sea water. Journal of the Acoustical Society of America, 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. Journal of the Acoustical Society of America, 72(6):1879-1890.

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

See also

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"))