oce (version 0.9-18)

swSoundAbsorption: 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

frequency of sound in Hz

salinity

salinity in PSU

temperature

in-situ temperature [$^\circ$C], defined on the ITS-90 scale; see Temperature units in the documentation for swRho.

pressure

water pressure in dbar

pH

seawater pH

formulation

specify the formulation to use; 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 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.

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/

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"))