Experimental demonstration of remote, passive acousto-optic sensing

Area of Science:

• Acoustics
• Optics
• Oceanography

Background:

• Passive underwater sound detection is crucial for monitoring marine environments.
• Current methods often require direct deployment of sensors, limiting aerial surveillance capabilities.
• Optical hydrophones offer a potential solution for remote, non-invasive acoustic sensing.

Purpose of the Study:

• To investigate the feasibility of an optical hydrophone for remote, aerial detection of underwater sound.
• To assess the performance of an acousto-optic sensor system under various sea surface conditions.
• To develop and test a laser-based system for tracking surface reflections.

Main Methods:

• Utilizing a laser beam directed at the water surface to measure vibration-induced phase modulation.
• Employing a laser Doppler vibrometer to detect acoustically generated surface vibrations.
• Integrating a laser-based surface normal glint tracker to maintain laser alignment on the specularly reflecting water surface.

Main Results:

• Demonstrated the principle of acousto-optic sensor detection on both hydrostatic and hydrodynamic surfaces.
• Validated the effectiveness of the laser Doppler vibrometer and glint tracker system in laboratory settings.
• Presented experimental results comparing sensor performance under different sea surface conditions.

Conclusions:

• The acousto-optic sensor system shows promise for remote, aerial detection of underwater sound.
• Maintaining laser alignment is critical for signal detection, and the glint tracker effectively mitigates this challenge.
• Further research and development could lead to practical applications in naval acoustics and marine surveillance.