Shearography Simulation via Phase Screens and Separable OTFs
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Solution Overview
Problem
Current methods for simulating shearographic imaging are cumbersome due to difficulties in capturing phase information and diffraction effects, particularly in airborne systems, where sequential ray tracing is inefficient and aperture size increases degrade image quality.
Innovation Solution
A computational method that generates simulated scenes with variable optical properties, applies shear conditions as numerical phase screens, computes optical transfer functions, and convolves them with electromagnetic fields to create sheared specklegrams, optimizing diffraction computations by treating the optical transfer function as a sum of separable functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sequential ray tracing is used to simulate shearographic imaging, then phase information can be captured, but the simulation becomes cumbersome and inefficient due to the need to track microscopic changes in very long path lengths
Solution Approach 1:
The patent replaces sequential ray tracing (a computational/mechanical process) with a wave optics-based simulation approach that uses optical transfer functions and electromagnetic field propagation. This substitution eliminates the need to track individual ray paths and their phase changes, instead using wave equations to compute the overall optical field, thereby improving simulation efficiency while maintaining phase information accuracy.
Solution Approach 2:
The patent changes the fundamental parameters of the simulation by transitioning from ray-based parameters (path lengths, angles) to wave-based parameters (optical transfer functions, electromagnetic fields). This parameter transformation allows phase information to be captured through the optical transfer function formalism rather than through cumulative ray path tracking, resolving the efficiency problem.
2Measurement precision
If aperture size is increased to improve image quality in conventional imaging, then resolution improves, but in shearography the finite-sized optical-blur function from diffraction is necessary and increasing aperture size degrades image quality
Solution Approach 1:
The patent addresses the aperture size contradiction by changing the simulation parameters to include diffraction effects through optical transfer functions. The wave optics approach naturally incorporates the finite aperture's diffraction pattern into the simulation, allowing the system to model the optimal aperture size that produces the necessary optical blur for shearography without requiring physical aperture adjustments or complex trial-and-error design iterations.
3Ease of manufacture
If sequential ray tracing is used, then imaging simulation can be performed, but capturing diffraction effects becomes cumbersome
Solution Approach 1:
The patent replaces the ray tracing mechanism with a wave optics mechanism that inherently captures diffraction effects. By using electromagnetic field propagation and optical transfer functions, the simulation naturally includes diffraction without requiring special handling or complex computational procedures, thus improving both ease of implementation and accuracy of diffraction effect capture.
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
This approach enables efficient simulation and optimization of shearography systems, avoiding the inefficiencies of sequential ray tracing and improving image quality by accurately modeling phase and diffraction effects, thus enhancing system design and performance prediction.
Implementation Method 1
diffraction from an aperture of a shearographic imager is important for shearography. A finite-sized optical-blur function, such as that caused by diffraction, is typically necessary for shearography.
Implementation Method 2
convolving, for each of the at least two sheared specklegrams, the at least one separable OTF with the simulated scene to simulate electromagnetic (EM) fields of each of the at least two sheared specklegrams
Implementation Method 3
generating at least two shear conditions, relative to the reference shear, expressed as numerical phase screens
Data Source
AI summary
Systems and methods for computationally simulating and optimizing shearography systems are provided. The systems and methods for simulation and optimization avoid ray tracing, and, instead, implement a phase screen approach to image computation. The systems and methods include physics-based surface texture and surface motion simulations, the application of phase screens to computer-generated simulations of shearographic remote sensing, and the inclusion of de-polarization due to multiple scattering and birefringence at a surface being imaged. The systems and methods include further greatly optimize diffraction computations by treating an optical transfer function (OTF) of an arbitrary aperture as a sum of separable OTFs.