Methods and systems for measurement and estimation of normalized contrast in infrared thermography
Inventors
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-9787913-B1
Publication Date
2017-10-10
Expiration Date
2030-12-17
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Abstract
Methods and systems for converting an image contrast evolution of an object to a temperature contrast evolution and vice versa are disclosed, including methods for assessing an emissivity of the object; calculating an afterglow heat flux evolution; calculating a measurement region of interest temperature change; calculating a reference region of interest temperature change; calculating a reflection temperature change; calculating the image contrast evolution or the temperature contrast evolution; and converting the image contrast evolution to the temperature contrast evolution or vice versa, respectively.
Core Innovation
The invention provides methods and systems for converting an image contrast evolution of an object to a temperature contrast evolution and vice versa, including steps such as assessing an emissivity of the object, calculating afterglow heat flux evolution, calculating measurement and reference regions of interest temperature changes, calculating reflection temperature changes, and performing the conversion between image contrast evolution and temperature contrast evolution.
The invention addresses the problem that normalized image (pixel intensity) contrast and normalized temperature contrast differ for objects having emissivity values less than one, which can lead to inaccuracies when these quantities are treated as equivalent. The invention solves this by establishing formulas and methods to estimate normalized temperature contrast from normalized pixel intensity contrast, accounting for reflection temperature evolution and afterglow effects to improve accuracy in non-destructive evaluation using infrared flash thermography.
Claims Coverage
The patent presents six main inventive features disclosed across independent claims relating to methods and apparatuses for converting between image contrast evolution and temperature contrast evolution, assessing object emissivity, and calculating afterglow heat flux evolution.
Method for converting image contrast evolution to temperature contrast evolution
The method involves calculating measurement and reference region of interest temperature changes and reflection temperature change, calculating image contrast evolution, and converting this image contrast evolution to temperature contrast evolution using a processor according to specified equations.
Method for calculating image contrast evolution using temperature measurements
The method calculates the image contrast evolution by measuring measurement, reference, and reflection temperatures and applying a defined equation to determine the image contrast evolution.
Method for calculating image contrast evolution using reflection pixel intensity and camera constant
The method measures measurement and reference temperatures, reflection pixel intensity, calculates a camera constant, and computes the image contrast according to a provided formula.
Calculation of camera constant
The camera constant is calculated using an equation that relates pixel intensities from high emissivity tape and high reflectivity foil, emissivity values, and pre-flash temperature values.
Method for assessing object emissivity
The method measures a pre-flash pixel intensity, calculates a camera constant, and computes object emissivity using an equation relating these values and parameters B and J derived from measurements of tape and foil regions.
Method for calculating afterglow heat flux evolution
This method measures a reflection temperature and calculates afterglow heat flux evolution using the Stefan-Boltzmann constant and the difference between reflected temperature to the fourth power post-flash and pre-flash.
The claims collectively cover innovative methods and apparatuses for precise conversion between image and temperature contrast evolutions by incorporating emissivity, reflection temperature, camera constants, and afterglow heat flux, enhancing accuracy in infrared flash thermography data processing and enabling emissivity assessment and heat flux modeling.
Stated Advantages
Improved accuracy in processing infrared thermography data by distinguishing and converting between normalized pixel intensity contrast and normalized temperature contrast for objects with emissivity less than one.
Capability to measure reflection temperature evolution and model afterglow flux leading to better estimation of temperature contrast evolution and image contrast profiles.
Provision of a technique to estimate object emissivity in real-time using the same infrared camera system during thermography.
Ability to model the compound heat source flux evolution including thermal afterglow for improved simulation and data analysis.
Documented Applications
Non-destructive evaluation (NDE) of thin materials such as laminated or bonded composites in the aerospace industry using infrared flash thermography.
Detection of delamination-like anomalies and surface cracks via IR flash thermography.
Use in IR flash thermography systems involving flash lamps, flash hoods, IR cameras, and computer-controlled data acquisition for inspecting test objects.
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