Phase Resolved Shearography for Buried Object Detection
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Solution Overview
Problem
Non-phase resolved shearography is unable to resolve the phase of acousto-seismic signals, requiring high power laser sources and is impractical for fast-moving platforms, limiting its ability to detect buried objects and requiring further image processing to improve visibility of fringe patterns due to noise and low contrast.
Innovation Solution
A method involving phase stepping of laser beam images with a shearing interferometer to collect and compare specklegrams, allowing for phase-resolved shearography that enhances the signal-to-noise ratio and improves fringe contrast by eliminating random speckle phase noise, enabling the detection of buried objects with improved accuracy and clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If non-phase resolved shearography is used to detect buried objects, then the system can operate with simpler processing, but it cannot resolve the phase of acousto-seismic signals and requires high power laser sources
Solution Approach 1:
The patent applies parameter changes by transitioning from non-phase resolved to phase resolved shearography, utilizing phase stepping techniques to resolve the phase of acousto-seismic signals. This allows the system to extract both amplitude and phase information, enabling inversion methods to identify scattering sources while reducing laser power requirements
2Device complexity
If non-phase resolved shearography is used, then the system setup is simpler, but it is impractical for aircraft and fast moving platforms that require large area coverage rates
Solution Approach 1:
The patent implements dynamics by adapting shearography for use on moving platforms such as aircraft. The system captures sequential images at different positions along the flight path and processes them to reconstruct shearograms, enabling large area coverage rates while maintaining measurement quality on fast-moving platforms
3Measurement precision
If difference images are processed to improve visibility of fringe patterns, then the contrast and signal to noise ratio improve, but the processing complexity increases
Solution Approach 1:
The patent applies preliminary action by performing phase stepping during image acquisition rather than relying solely on post-processing. By capturing multiple images at different phase steps and processing them to generate shearograms, the system improves fringe contrast and signal-to-noise ratio while reducing the complexity of subsequent image processing operations
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
The method achieves enhanced detection of buried objects by improving the signal-to-noise ratio and clarity of fringe patterns, allowing for real-time monitoring of surface changes and subsurface structures with reduced processing burden and increased accuracy.
Implementation Method 1
phase stepping the first, second and third reflected laser beam images with a shearing interferometer
Implementation Method 2
The two images are coherently superposed. The lateral displacement is called the shear of the images. The superposition of the two images is called a shearogram
Implementation Method 3
reflecting sequentially off of a target surface first, second and third laser beams
Implementation Method 4
detect the presence of buried objects (e.g. mines, tunnels etc.)... the full phase and amplitude information of small scale acousto-seismic vibrations
Data Source
AI summary
A shearography system and method provide advances allowing for rapid processing to produce shearograms which provide surface motion information which may be helpful in multiple fields. For instance, amongst virtually endless possibilities, the system and method may allow for detection of underground structures or ordnance and or be used in the medical field to provide non-contact sensing of a person's internal structures or movements.