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KRM

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

Overview

Benchmarked Validated
Theory Implementation

The Kirchhoff-ray mode model (KRM) calculates composite monostatic backscatter from a fish body and an explicitly represented gas-filled swimbladder.

Core idea

Treat the segmented flesh body with a Kirchhoff-style approximation, use an acoustic-size-dependent mode or ray description for the swimbladder, and combine the component amplitudes coherently (Clay 1991; Clay and Horne 1994).

Best for

  • Gas-bearing fish with separate body and swimbladder outlines
  • Frequency and orientation studies where the internal gas component dominates or interferes with the body return
  • Comparison of supported KRM material and embedding variants

Supports

  • SBF objects with body and swimbladder shapes, placement, and orientation
  • Separate body and bladder material descriptions
  • Stored body, swimbladder, and coherently combined outputs

Main assumptions

  • Segment-wise body and simplified swimbladder approximations
  • The selected KRM variant matches the intended material interpretation
  • Coherent first-order component combination
  • No fully coupled body-swimbladder boundary solve or repeated rescattering

Validation status

  • Benchmarked against the canonical spectra stored in benchmark_ts.
  • Validated against KRMr, echoSMs, and the NOAA KRM applet on bundled fish objects and shared workflows.

Family pages

  • Implementation: building fish objects, variants, component output, and comparisons
  • Theory: body term, swimbladder branches, and coherent 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.