Deep sediment heterogeneity inferred using very low-frequency features from merchant shipsa)

Area of Science:

• Ocean acoustics
• Seismic signal processing
• Marine geophysics

Background:

• Merchant ship noise offers a valuable broadband sound source for studying deep seabed layers.
• Ship spectrograms exhibit nested striations, acoustic features linked to the waveguide invariant (β) becoming infinite.

Purpose of the Study:

• To identify β = ∞ frequencies in ship noise spectrograms.
• To perform statistical inference on deep layer sound speeds and thicknesses in the New England Mudpatch.
• To expand upon previous studies by including more ships, acoustic arrays, and a larger geographical region.

Main Methods:

• Identification of singular points (β = ∞ frequencies) in ship noise time-frequency spectrograms.
• Feature-based inversion using these singular points to estimate seabed acoustic properties.
• Correlation analysis between spatial variability of deep layer sound speeds and ship tracks to examine heterogeneity.

Main Results:

• Singular points were identified within the 20–80 Hz frequency range.
• Feature-based inversion provided estimates for the sound speed and a limiting value for the thickness of the first deep layer.
• Spatial variability in deep layer sound speeds was examined in relation to ship tracks.

Conclusions:

• The study successfully utilized ship noise features to infer deep seabed acoustic properties.
• The method provides estimates for sound speed and layer thickness, with potential for heterogeneity analysis.
• This approach offers a scalable method for seabed characterization using ambient noise sources.