Modelling approaches to multibeam echosounders for sound field characterizationa)

Area of Science:

• Marine acoustics
• Bioacoustics
• Environmental impact assessment

Background:

• Growing concerns regarding the effects of multibeam echosounders (MBES) on marine ecosystems.
• The necessity of precise acoustic modeling for evaluating the impact of anthropogenic sound sources.
• The 2022 Joint Industry Program Acoustic Modelling Workshop established verification scenarios for deep-water MBES.

Purpose of the Study:

• To compare and validate different modeling approaches for deep-water multibeam echosounders (MBES).
• To assess the agreement between various acoustic models in predicting sound fields.
• To calculate and compare key acoustic metrics essential for marine life impact assessments.

Main Methods:

• Utilized several acoustic models to compute MBES beam patterns and propagated acoustic fields.
• Employed geometrical acoustics and ray-tracing techniques for sound propagation analysis.
• Calculated and compared key acoustic metrics, including cumulative sound exposure and threshold ranges for marine mammals.

Main Results:

• Geometrical acoustics proved well-suited for the unique radiation patterns of MBES.
• Ray-tracing models demonstrated relevance at short ranges and long horizontal distances with sound speed gradients.
• Accurate near-field modeling significantly influenced final acoustic metrics and impact ranges for marine mammals.

Conclusions:

• Validated acoustic modeling approaches for MBES, confirming the suitability of geometrical acoustics.
• Highlighted the importance of accurate near-field sound propagation modeling for realistic impact assessments.
• Emphasized that cumulative sound exposure is primarily determined by the main transmit beam of MBES sectors.