Physics-Based Models for Acoustic Target Strength

Acoustic target strength (TS) represents the intensity of an echo returning from an individual scatterer such as bubbles, fish, or zooplankton. TS can be used to convert integrated or volumetric backscatter collected from fisheries acoustic surveys into units of number density (e.g. animals per m^3), abundance (e.g. number of animals), and biomass (e.g. kg). This parameter can also be used to aid in classifying backscatter, such as separating likely echoes of large predatory fish (e.g. adult cod) from smaller prey (e.g. shrimp). One way to estimate TS is to use physics-based models to calculate theoretical TS that comprise exact and approximate solutions as well as analytical approaches. The models provided can help provide TS estimates over broad statistical distributions of model parameters. Applications are described by Lucca et al. (2023) , with fisheries-acoustics principles from Simmonds and MacLennan (2005) .

acousticTS

acousticTS estimates the acoustic target strength of aquatic organisms, calibration spheres, and other individual scatterers with physics-based models. It provides one interface for defining geometry and material properties, running compatible scattering models, and comparing results across frequency, orientation, and morphology.

Package workflow

The package separates geometry, physical interpretation, and model execution:

Shapes and scatterers are implemented as S4 objects. A Shape stores geometry. A Scatterer adds the physical properties, orientation, model inputs, and results needed for an acoustic calculation.

Installation

Install the latest version on CRAN:

install.packages("acousticTS")

Or install the latest developments from the current GitHub version:

install.packages("remotes")
remotes::install_github("brandynlucca/acousticTS")

[!NOTE] acousticTS contains C++17 and Fortran source code. Windows users need the version of Rtools matching their R installation. macOS users need the Xcode Command Line Tools and a compatible GNU Fortran compiler. Linux users need a C++17 compiler, make, and gfortran. See Troubleshooting if compilation fails.

Quick start

Build a shape, attach its acoustic properties, and run a model:

library(acousticTS)

# 1. Build a geometric Shape
krill_shape <- cylinder(
  length_body = 0.03,
  radius_body = 0.003
)

# 2. Wrap it as a fluid-like Scatterer
krill_target <- fls_generate(
  shape = krill_shape,
  g_body = 1.0357,
  h_body = 1.0279,
  theta_body = pi / 2
)

# 3. Calculate and plot target strength
krill_target <- target_strength(
  object = krill_target,
  frequency = seq(38e3, 120e3, by = 2e3),
  model = "dwba"
)

plot(krill_target, type = "model")

The result remains attached to krill_target, so the same object can be plotted, inspected with extract(), or reused in a simulation.

What is included

• Constructors for canonical and arbitrary shapes, including spheres, spheroids, cylinders, and digitized body profiles.
• S4 scatterer classes for fluid-like, gas-filled, elastic, composite, and calibration targets.
• Exact, modal-series, T-matrix, weak-scattering, high-frequency, and composite model families.
• Shape manipulation and reforge() workflows for resizing, resampling, bending, and repositioning targets.
• Repeated parameter studies with simulate_ts().
• Stored-state T-matrix tools for angular scattering, bistatic summaries, and orientation averages.
• Validation registries, benchmark datasets, and documented implementation checks.

Use available_models() for the current model registry and accepted aliases.

Example data

The package includes ready-to-use biological targets and benchmark results:

data(krill, package = "acousticTS")
data(cod, package = "acousticTS")
data(sardine, package = "acousticTS")
data(benchmark_ts, package = "acousticTS")

plot(krill, type = "shape")

See Example Data for the contents and intended use of each object.

Documentation

• Quick Start
• Build Targets
• Run Models
• Model Library
• Function Reference

The documentation explains package conventions, supported formulations, and validation scope. It complements the original scattering literature rather than replacing it.

Citation

To cite acousticTS, run:

citation("acousticTS")

The Zenodo concept DOI, which resolves to the latest archived release, is 10.5281/zenodo.7600659.

Contributing

Bug reports and feature requests are welcome through GitHub Issues. Please include a minimal reproducible example and sessionInfo() when reporting a problem.

acousticTS is licensed under GPL-3. Upstream code attribution and license notices are provided in inst/COPYRIGHTS.