Acoustic optic hybrid (AOH) sensor

Area of Science:

• Acoustics
• Optics
• Oceanography

Background:

• Underwater acoustic sensing traditionally relies on hydrophones.
• Laser vibrometers offer a non-contact method for detecting surface vibrations.
• Previous research has explored optical methods for underwater detection.

Purpose of the Study:

• To establish and evaluate the capability of laser vibrometers to detect acoustic echoes from submerged targets.
• To demonstrate the feasibility of using laser vibrometers for underwater acoustic sensing.
• To quantify the effects of surface waves on echo retrieval and develop a 3D imaging system.

Main Methods:

• Utilizing a laser vibrometer to collect sonar echoes from the water surface.
• Conducting experiments to quantify the impact of capillary and gravity waves on echo retrieval.
• Implementing data acquisition and beamforming techniques for 3D image reconstruction.
• Developing a three-dimensional, acoustic-optic, synthetic aperture sonar (SAS).

Main Results:

• Demonstrated feasibility of sensing underwater sound using laser vibrometers.
• Achieved signal-to-noise ratios (SNR) from 6 to 46 dB for acoustic excitation levels of 168 to 195 dB re: 1 microPa.
• Quantified the destructive effects of surface waves on echo retrieval.
• Successfully acquired echoes and generated 3D images of a submerged target.

Conclusions:

• Laser vibrometers are effective for detecting underwater sonar echoes.
• Surface wave mitigation is crucial for optimal performance.
• The developed acoustic-optic SAS system shows promise for enhanced underwater surveillance and mapping.
• This technique offers potential for increased safety and fuel efficiency in airborne towed sonar systems.