Underwater acoustics

API reference

soundspeed(temperature=27, salinity=35, depth=0; γ=0, cₐ=340, ρᵣ=1000)

Compute sound speed in water in m/s, given:

  • water temperature in °C
  • salinity in ppt
  • depth in meters
  • void fraction (γ) in bubbly water
  • sound speed in gas (cₐ) if γ > 0
  • ratio of density of water to gas (ρᵣ) if γ > 0

Implementation based on Mackenzie (1981), Wood (1964) and Buckingham (1997).

shearspeed(c)

Compute shear wave speed based on compressional wave speed c using a regression relationship from Hamilton (1980).

absorption(frequency, distance=1000, salinity=35, temperature=27, depth=0, pH=8.1)

Compute volume acoustic absorption coefficient in water, given:

  • frequency in Hz
  • distance in meters
  • salinity in ppt
  • water temperature in °C
  • depth in meters
  • pH of water

The result is a unitless linear scale factor for sound pressure over the given distance. To get absorption in terms of dB / m, set distance = 1.0 and convert the result to decibels. For instance, at a frequency of 100 kHz:

julia> A = absorption(100e3, 1.0)
0.9959084838594522

julia> α = -20log10(A)
0.035611359656810865

Implementation based on the Francois and Garrison (1982) model.

water_density(temperature=27, salinity=35)

Compute density of water (kg/m³), given temperature in °C and salinity in ppt.

Implementation based on Fofonoff (1985 - IES 80).

dBperλ(x)

Compute dimensionless absorption coefficient δ from dB/λ. Implementation based on APL-UW TR 9407 (1994), IV-9 equation (4).

in_dBperλ(δ)

Compute dB/λ from dimensionless absorption coefficient δ. Implementation based on APL-UW TR 9407 (1994), IV-9 equation (4).

reflection_coef(θ, ρᵣ, cᵣ, δ=0.0)

Compute complex reflection coefficient at a fluid-fluid boundary, given:

  • angle of incidence θ (angle to the surface normal)
  • relative density of the reflecting medium to incidence medium ρᵣ
  • relative sound speed of the reflecting medium to incidence medium cᵣ
  • dimensionless absorption coefficient δ

Implementation based on Brekhovskikh & Lysanov. Dimensionless absorption coefficient based on APL-UW Technical Report 9407.

surface_reflection_coef(windspeed, frequency, θ)

Compute surface reflection coefficient, given:

  • windspeed in m/s
  • frequency in Hz
  • angle of incidence θ (angle to the surface normal)

Implementation based on the APL-UW Technical Report 9407 II-21.

bubble_resonance(radius, depth=0; γ=1.4, p₀=1.013e5, ρ=1022.72, g=9.80665)

Compute resonance frequency of a freely oscillating has bubble in water, given:

  • bubble radius in meters
  • depth of bubble in water in meters
  • gas ratio of specific heats ‘γ’
  • atmospheric pressure ‘p₀’ in Pa
  • density of water ‘ρ’ in kg/m³
  • acceleration due to gravity ‘g’ in m/s²

This ignores surface-tension, thermal, viscous and acoustic damping effects, and the pressure-volume relationship is taken to be adiabatic. Implementation based on Medwin & Clay (1998).

doppler(speed, frequency)
doppler(speed, frequency, soundspeed)

Compute Doppler frequency, given relative speed between transmitter and receiver in m/s. soundspeed is the nominal sound speed in water.