Bottom interacting sound at 50 km range in a deep ocean environment

Area of Science:

• Oceanography
• Acoustics
• Geophysics

Background:

• Ocean acoustic propagation experiments provide data on acoustic pulse intensities and travel times.
• Seafloor reflections are a significant factor in acoustic signal behavior, particularly at shorter ranges.
• Interference between bottom-reflected (BR) and surface-reflected, bottom-reflected energy affects refracted arrivals.

Purpose of the Study:

• To analyze the effects of seafloor reflections on acoustic pulses at approximately 50 km range.
• To investigate the necessity of accounting for bottom-reflected paths in acoustic propagation analysis.
• To understand how high mode number energy in BR arrivals aliases into low mode numbers.

Main Methods:

• Analysis of a subset of data from the 2004 Long-range Ocean Acoustic Propagation Experiment.
• Acoustic modeling using the parabolic equation method.
• Modeling the seafloor as a fluid layer without rigidity, 3D effects, or scattering.

Main Results:

• Inclusion of range-dependent bathymetry in acoustic models is essential for accurate data fitting.
• A good model-data fit was achieved for sub-bottom properties estimated from the experimental data.
• Bottom-reflected energy interferes with refracted arrivals and aliases into lower acoustic modes.

Conclusions:

• Knowledge of bottom-reflected paths is necessary for a comprehensive understanding of acoustic processes, including low mode number phenomena.
• Accurate acoustic modeling requires consideration of seafloor properties and bathymetry.
• The study successfully estimated sub-bottom properties using acoustic data and modeling.