A fluctuation-based method for tonal source depth discrimination using a vertical line array in shallow ocean

Area of Science:

• Underwater acoustics
• Signal processing
• Oceanography

Background:

• Distinguishing source depths is crucial for underwater acoustic applications.
• Amplitude fluctuation differences offer a mechanism for source depth discrimination.
• Existing methods like modal scintillation face limitations with vertical line array (VLA) span.

Purpose of the Study:

• To enhance binary source depth discrimination in shallow ocean environments.
• To overcome the performance limitations of existing methods, especially under reduced VLA span conditions.
• To develop a robust method for differentiating surface and submerged acoustic sources.

Main Methods:

• Analysis of physical mechanisms behind amplitude fluctuations.
• Exploitation of modal orthogonality to enhance fluctuation differences without modal decomposition.
• Development of a normalized amplitude fluctuation index for VLA application.
• Integration of signal power across the VLA to suppress interference and preserve depth-dependent fluctuations.

Main Results:

• The proposed method demonstrates robust distinction between surface and submerged sources, independent of source range.
• Simulation results show superior depth discrimination compared to the Modified Modal Scintillation Index method under limited VLA spans.
• Experimental validation using SWellEx-96 data confirms improved discrimination performance.

Conclusions:

• Modal orthogonality effectively enhances amplitude fluctuation differences for improved source depth discrimination.
• The normalized amplitude fluctuation index provides a reliable metric for VLA-based source depth identification.
• The proposed technique offers a significant advancement for underwater acoustic source localization, particularly in challenging shallow water conditions.