Mid-frequency sound propagation and attenuation through a biological deep scattering layer

Area of Science:

• Oceanography
• Acoustics
• Marine Biology

Background:

• Environmental variability impacts acoustic propagation and scattering.
• Deep scattering layers (DSL) are biological sound scatterers.
• Previous studies have not fully accounted for DSL effects on acoustic signals.

Purpose of the Study:

• Investigate the effect of environmental variability on acoustic propagation and scattering.
• Quantify the acoustic attenuation caused by a DSL.
• Improve acoustic propagation models by incorporating DSL and physical oceanographic data.

Main Methods:

• Deployed an acoustic autonomous underwater vehicle (AUV) for data collection.
• Utilized a prolate spheroid gas-filled swimbladder scattering model to estimate DSL acoustic attenuation.
• Employed a parabolic equation model to simulate transmission loss and account for physical oceanographic variability.

Main Results:

• A biological deep scattering layer (DSL) was identified approximately 100m below the AUV mission depth.
• The DSL was estimated to cause 1-1.5 dB/km of acoustic attenuation.
• Incorporating DSL attenuation and physical oceanography improved acoustic propagation path comparison results.

Conclusions:

• Biological scattering from DSLs significantly affects acoustic propagation.
• Accurate acoustic attenuation studies must consider both biological scattering and physical oceanographic variability.
• The findings enhance the understanding of sound propagation in marine environments.