Direction of arrival estimation with a vector intensity hydrophone array towed by an autonomous surface vehicle

Area of Science:

• Ocean acoustics
• Array signal processing
• Underwater navigation

Background:

• Direction of Arrival (DOA) finding is crucial for underwater acoustic localization.
• Traditional methods often rely on bulky or less sensitive sensors.
• Vector sensors offer directional information but can be complex and expensive.

Purpose of the Study:

• To demonstrate a compact hydrophone array emulating vector sensor DOA performance.
• To assess the array's capability in determining horizontal DOA of low-frequency signals.
• To validate DOA finding performance in a deep-water, long-range experimental setting.

Main Methods:

• Development of a 33-cm, four-element, tetrahedron-shaped hydrophone array.
• Deployment of the array from an autonomous surface vehicle in deep water.
• Application of pressure gradient-based methodology for DOA estimation.
• Utilizing both coherent and incoherent DOA finding techniques.

Main Results:

• The tetrahedron hydrophone array successfully emulated low-frequency DOA finding performance.
• Horizontal DOA (bearing) was determined for low-frequency (210-310 Hz) transmissions.
• Effective DOA determination was achieved for sources at ~1100 m depth and up to 176 km range.
• Consistent DOA values were obtained for signal-to-noise ratios above 11 dB.

Conclusions:

• The compact tetrahedron hydrophone array is a viable alternative to vector sensors for low-frequency DOA finding.
• The demonstrated system offers effective long-range acoustic source localization in deep-water environments.
• The pressure gradient-based methodology provides robust performance across various signal-to-noise ratios.