Airborne Interferometry for Underwater Sound Source Triangulation
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Solution Overview
Problem
Current interferometry techniques struggle to effectively distinguish and locate sound sources underwater due to the interference between acoustic waves and gravity-capillary waves at the water's surface, as conventional assumptions treat the water surface as rigid and immobile under acoustic excitation, masking the microscopic movements induced by sound waves.
Innovation Solution
The system employs wide-field imaging interferometry and Range-Sheared Interferometry to detect the microscopic movements of the water surface caused by sound waves, exploiting the differences in amplitude, frequency-velocity dispersion, and wavelength between acoustic and gravity-capillary waves, allowing for the separation and detection of sound waves amidst the larger background waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional interferometry techniques are used to detect water surface movements, then the detection capability is limited by the assumption of rigid water surface, but the microscopic movements induced by sound waves can be detected with laser interferometry
Solution Approach 1:
The patent uses laser interferometry as an intermediary measurement technique to detect the microscopic water surface movements caused by sound waves. The laser beam acts as a mediator that interacts with the water surface and converts the mechanical surface displacement into measurable optical interference patterns, enabling precise detection without direct contact with the water
Solution Approach 2:
The patent replaces conventional mechanical or contact-based detection methods with optical laser interferometry. By substituting the mechanical measurement approach with an optical field-based measurement, the system achieves non-contact, high-precision detection of water surface movements while avoiding the limitations of rigid surface assumptions
2Measurement precision
If the water surface is treated as rigid under acoustic excitation, then the measurement system is simplified, but the sound wave detection accuracy deteriorates due to masking by gravity-capillary waves
Solution Approach 1:
The patent transitions from treating the water surface as a static rigid boundary to modeling it as a dynamic, deformable interface that responds to acoustic excitation. By incorporating the water surface's actual physical response to sound waves into the interferometry measurement model, the system can distinguish acoustic-induced surface movements from other surface wave phenomena
Solution Approach 2:
The patent changes the measurement parameters by focusing on specific characteristics of water surface movements that are unique to acoustic excitation, such as the frequency-velocity dispersion relationship and the specific amplitude patterns. By analyzing these changed parameters, the system can differentiate sound wave effects from gravity-capillary waves
3Area of stationary object
If wide-field imaging interferometry is used to capture large area surface movements, then the field of view is increased, but the ability to resolve microscopic displacements may be compromised
Solution Approach 1:
The patent segments the wide field of view into multiple measurement zones or uses a grid pattern of laser beams across the water surface. By dividing the large area into smaller sub-areas, each with its own interferometry measurement, the system maintains high resolution for microscopic displacements while covering an extended spatial domain
Solution Approach 2:
The patent enhances the measurement capability by adding temporal dimension to the spatial wide-field measurement. By capturing interferometry patterns at multiple time points and analyzing the dynamic evolution of surface movements, the system achieves both wide field of view and high precision in detecting microscopic acoustic-induced displacements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the detection and location of underwater sound sources by filtering out gravity-capillary waves and focusing on the faster-moving sound waves, using laser interferometry to capture microscopic surface changes and triangulate the sound source's position.
Implementation Method 1
two copies of the incoming image electromagnetic (EM) field are generated. One copy of the image EM field is optically displaced laterally relative to the other, then the two image EM fields are then combined on a single focal plane to create an image
Implementation Method 2
a target surface, part, or area being observed is illuminated by an expanding laser beam
Implementation Method 3
sound waves do move the sea surface, with typically microscopic amplitudes
Implementation Method 4
the detailed mechanism of pressure release
Implementation Method 5
the laser-illuminated area is viewed through a beam-splitter or similar device designed so that two copies of the incoming image electromagnetic (EM) field are generated. One copy of the image EM field is optically displaced laterally relative to the other
Data Source
AI summary
An interferometry system and method thereof detects movements of the surface of a body of water in response to acoustic waves generated from a sub-surface source interacting with the surface. Movements of the surface of the body of water are viewed over multiple interferometric images that can be pieced together to generate an interferometric movie or video. The interferometric movie or video depicts the movement of the acoustic wave propagating through the viewing area. Once the movement of the acoustic wave propagating through the viewing area is known, then back propagation techniques are employed to determine or triangulate the location of the sub-surface source that generated the acoustic wave.