Sound scattering by several zooplankton groups. II. Scattering models

Area of Science:

• Acoustics
• Marine Biology
• Biophysics

Background:

• Zooplankton acoustic scattering is complex and depends on anatomy.
• Previous work established acoustically inferred boundary conditions for zooplankton.
• Understanding acoustic scattering is crucial for biomass estimation and ecosystem monitoring.

Purpose of the Study:

• To develop and validate mathematical scattering models for different zooplankton anatomical groups.
• To compare model predictions with experimental acoustic backscattering data.
• To identify dominant scattering mechanisms for various zooplankton types.

Main Methods:

• Utilized a combination of ray theory, modal-series solutions, and distorted wave Born approximation (DWBA).
• Developed specific models for fluidlike (euphausiids), elastic-shelled (gastropods), and gas-bearing (siphonophores) zooplankton.
• Applied models to analyze single pings, ping-to-ping variability, and averaged echo data.

Main Results:

• Models qualitatively described target strength versus frequency for single pings.
• DWBA-based models predicted echo levels across all angles of incidence, including end-on.
• A hybrid model combining exact gas sphere solutions and DWBA was developed for gas-bearing animals.
• Reasonable qualitative and quantitative agreement was found between model predictions and experimental data.

Conclusions:

• The developed mathematical scattering models provide a robust framework for predicting zooplankton acoustic responses.
• The models successfully account for diverse anatomical structures and scattering mechanisms.
• These findings advance the acoustic characterization of zooplankton for ecological studies.