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Body-backbone composite model (BBFM)

Source: R/model-bbfm.R
BBFM.Rd

Computes a coherent composite backscatter prediction for swimbladder-less fish represented as a weakly scattering flesh body plus an explicit elastic backbone. The flesh contribution is evaluated with the distorted-wave Born approximation (DWBA), while the backbone contribution is evaluated with the elastic cylinder modal-series solution (ECMS). The backbone amplitude is then translated into the stored body coordinate frame using a phase factor based on the backbone centroid before the two complex amplitudes are summed.

Usage

This model is accessed via:


target_strength(
  ...,
  model = "BBFM",
  sound_speed_sw,
  density_sw,
  m_limit
)

Arguments

sound_speed_sw

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

density_sw

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

m_limit

Optional modal truncation limit passed to the backbone ECMS solve.

Theory

The model follows the same structural decomposition used for swimbladder-less mackerel by Gorska, Ona, and Korneliussen (2005): the flesh is treated as a weakly scattering fluid-like body, and the backbone is treated as an elastic cylindrical structure. In this implementation, the total complex backscattering amplitude is $$ f_{bs} = f_{\mathrm{flesh}} + f_{\mathrm{backbone}} \exp\left\{ 2 i k_{sw} v_c \right\}, $$ where \(f_{\mathrm{flesh}}\) is obtained from DWBA, \(f_{\mathrm{backbone}}\) is obtained from ECMS, and \(v_c = x_c \cos \theta + z_c \sin \theta\) is the projection of the stored backbone centroid onto the backscatter direction.

References

Gorska, N., Ona, E., and Korneliussen, R. (2005). Acoustic backscattering by Atlantic mackerel as being representative of fish that lack a swimbladder. Backscattering by individual fish. ICES Journal of Marine Science, 62: 984-995.

Stanton, T.K. (1988). Sound scattering by cylinders of finite length. II. Elastic cylinders. The Journal of the Acoustical Society of America, 83: 64-67.

Stanton, T.K. (1989). Sound scattering by cylinders of finite length. III. Deformed cylinders. The Journal of the Acoustical Society of America, 86: 691-705.

Stanton, T.K., Chu, D., and Wiebe, P.H. (1998). Sound scattering by several zooplankton groups. II. Scattering models. The Journal of the Acoustical Society of America, 103: 236-253.