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Viscous-elastic spherical model (VESMS)

Source: R/model-vesms.R
VESMS.Rd

Computes backscatter from a gas-filled spherical inclusion surrounded by an elastic shell and an outer viscous layer, following the wideband backscattering model used by Khodabandeloo et al. (2021). The model is parameterized on ESS objects, where the fluid slot represents the inner gas sphere and the shell slot represents the elastic shell. The external viscous layer is supplied as model-specific arguments.

Details

When radius_viscous and viscous_thickness are both omitted, the model estimates the viscous-layer radius from the neutral-buoyancy relation used by Khodabandeloo et al. (2021, Eq. 18).

Usage

This model is accessed via:


target_strength(
  ...,
  model = "VESMS",
  sound_speed_sw,
  density_sw,
  sound_speed_viscous,
  density_viscous,
  shear_viscosity_viscous,
  bulk_viscosity_viscous,
  radius_viscous,
  viscous_thickness,
  m_limit
)

Arguments

sound_speed_sw

Seawater sound speed (\(m~s^{-1}\)).

density_sw

Seawater density (\(kg~m^{-3}\)).

sound_speed_viscous

Compressional sound speed in the outer viscous layer (\(m~s^{-1}\)).

density_viscous

Density of the outer viscous layer (\(kg~m^{-3}\)).

shear_viscosity_viscous

Shear viscosity of the outer viscous layer (\(kg~m^{-1}~s^{-1}\)).

bulk_viscosity_viscous

Optional bulk viscosity of the outer viscous layer. When omitted, it defaults to the supplied shear viscosity to match the reference implementation.

radius_viscous

Optional outer radius of the viscous layer (\(R_2\), m).

viscous_thickness

Optional thickness of the viscous layer relative to the shell outer radius. Supply either this or radius_viscous, not both.

m_limit

Optional truncation limit for the modal summation. A value of 2 retains the \(m = 0, 1, 2\) terms. When omitted, the model uses \(\max(2, \mathrm{round}(k_1 R_2) + 10)\) at each frequency.

References

Khodabandeloo, B., Agersted, M.D., Klevjer, T., Macaulay, G.J., and Melle, W. (2021). Estimating target strength and physical characteristics of gas-bearing mesopelagic fish from wideband in situ echoes using a viscous-elastic scattering model. The Journal of the Acoustical Society of America, 149, 673-691.

Feuillade, C., and Nero, R.W. (1998). A viscous-elastic swimbladder model for describing enhanced-frequency resonance scattering from fish. The Journal of the Acoustical Society of America, 103, 3245-3255.

Anson, D.S., and Chivers, R.C. (1993). An irregular frequencies solution to acoustic scattering by elastic spheres. The Journal of the Acoustical Society of America, 93, 118-123.