Scatterer-class object for target strength estimation

The acousticTS package uses a variety of defined S4-class objects comprising different types of scatterers, such as fish with gas-filled swimbladders (SBF) and fluid-like crustaceans (FLS).

Slots

metadata

List containing relevant metadata

model_parameters

Model parameters necessary for predicting TS

Data Organization

metadata:

A list comprising any identifying information associated with the scatterer. The default metadata entry includes ID that uses a default character value of "UID" (i.e. ID = "UID"). This can otherwise be formatted in any manner for book keeping purposes.

body/bladder:

A list that includes information relevant to the scatterer's position vector, material properties, tilt/orientation, etc. For some scatterers, this may only include body, but other targets may have an additional parameter such as bladder. Generally, each entry includes:

• rpos: the relevant position vector (r₀) that includes axes such as x, y, z, etc., that depend on the type of scatterer being used.

• radius: in some cases this includes the radius measurements for each cylinders depending on the type of scatterer object.

• theta: the orientation of the scatterer relative to the transmitting transducer or sound source (θ_animal) that can be represented either by degrees or radians, although all functions require radians.

• g, h: material properties that represent the density and sound speed contrasts (g and h, respectively) relative to the ambient/surrounding fluid. Some targets may instead have standard sound speed (c_animal, m s^-1) and density (ρ_animal, kg m³).

shape_parameters:

A list that includes metadata pertaining to the shape of the scatterer and any other features of interest (e.g. gas-filled swimbladder). Generally, each entry includes: overall body length, the number of discrete cylinders that make up the shape (if applicable), and the units related to both θ_animal (e.g. rad, °) and length (e.g. mm, m).

model_parameters:

A list that contains relevant model parameterization once an object has been initialized for modeling σ_bs. This is typically broken up into three categories:

• parameters: A list that includes information such as frequency (Hz), acoustic wavenumber (i.e. k), etc.

• medium: A data.frame including information such as the material properties of the ambient medium.

• scatterer: A list containing summarized information used to parameterize certain scattering models.

model:

A list that collects model results from one or more models in the linear domain (i.e. σ_bs).

Supported Scatterers

• Elastic-based scatterers (ELA)

• Composite multi-component scatterers (CSC)

• Backboned fish (BBF)

• Calibration spheres (CAL)

• Elastic-shelled scatterers (ESS)

• Fluid-like scatterers (FLS)

• Gas-filled scatterers (GAS)

• Swimbladdered fish (SBF)