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KRM

Source: vignettes/krm/index.Rmd
index.Rmd

Overview

Benchmarked Validated
Theory Implementation

These pages follow the composite body-plus-swimbladder fish modeling literature initiated for cod and later generalized in open software implementations (C. S. Clay 1991; Clarence S. Clay and Horne 1994).

The Kirchhoff-ray mode model (KRM) is the package’s composite fish family for targets whose body and swimbladder occupy different acoustic regimes. It keeps a weakly contrasting ray-style body treatment and a separate swimbladder treatment that switches between low-mode and high-frequency behavior.

Core idea

Treat the fish body with a Kirchhoff-style short-segment approximation, treat the swimbladder with a simplified cylinder-based modal or high-frequency branch depending on acoustic size, and combine the complex component amplitudes coherently.

Best for

  • Gas-bearing fish whose body and swimbladder should not be modeled by the same exact family
  • Fish-like profile data represented by segmented body and bladder outlines
  • Practical fisheries workflows where composite body-plus-swimbladder structure matters

Supports

  • SBF composite scatterers
  • Body contrasts relative to seawater as medium 1 and swimbladder contrasts relative to the body in the local bladder subproblem
  • Monostatic composite target strength

Main assumptions

  • Short-segment ray-style treatment of the body
  • Simplified swimbladder physics chosen by acoustic size regime
  • Coherent component combination without a full coupled body-bladder boundary-value solve

Validation status

  • Benchmarked against canonical modal-family targets used for isolated gas-filled and weakly scattering cases.
  • Validated against KRMr, echoSMs, and the NOAA KRM applet on bundled fish objects and shared workflows.

Family pages

  • Implementation: scatterer setup, spectra, and validation tables
  • Theory: body Kirchhoff reduction, swimbladder mode/ray branches, and coherent composite sum

References

Clay, C. S. 1991. “Low-Resolution Acoustic Scattering Models: Fluid-Filled Cylinders and Fish with Swim Bladders.” The Journal of the Acoustical Society of America 89 (5): 2168–79. https://doi.org/10.1121/1.400910.
Clay, Clarence S., and John K. Horne. 1994. “Acoustic Models of Fish: The Atlantic Cod (Gadus Morhua).” The Journal of the Acoustical Society of America 96 (3): 1661–68. https://doi.org/10.1121/1.410245.