Methods and systems for measurement and estimation of normalized contrast in infrared thermography
Inventors
Assignees
National Aeronautics and Space Administration NASA
Publication Number
US-9066028-B1
Publication Date
2015-06-23
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 relates to methods and systems for converting an image contrast evolution of an object to a temperature contrast evolution and vice versa, including methods for assessing the emissivity of the object, calculating an afterglow heat flux evolution, and calculating measurement and reference region of interest (ROI) temperature changes as well as reflection temperature changes. It addresses processing digital data acquired from infrared (IR) thermography, specifically to analyze and process a series of IR video images obtained during non-destructive evaluation (NDE) of materials such as laminated or bonded composites.
The problem being solved arises from the difference between normalized image contrast (pixel intensity) and normalized temperature contrast for objects with emissivity values less than one. Existing methods treat these two contrasts as equivalent, which can lead to inaccuracies. The invention provides formulas and methods to estimate normalized temperature contrast from image contrast by measuring the reflection temperature evolution and incident heat flux, thereby improving accuracy in infrared thermography data analysis. The invention also includes techniques to assess emissivity in real-time and appropriately account for afterglow heat flux and reflection temperature in the measurement process.
Claims Coverage
The patent includes multiple independent claims focusing on apparatuses for converting image contrast evolution to temperature contrast evolution and vice versa, incorporating processors and memory units configured to compute temperature changes, reflection temperature changes, and contrast evolutions, and to perform the conversions using specified formulas.
Apparatus configured to convert image contrast evolution to temperature contrast evolution
An apparatus comprising one or more processors and memory units, configured to calculate measurement ROI temperature change ΔT, reference ROI temperature change ΔTref, reflection temperature change ΔTrefl, and image contrast evolution CWl, and to convert the image contrast evolution to the temperature contrast evolution Cl using a specified equation.
Incorporation of IR camera and related hardware for measurement and data acquisition
The apparatus further includes an IR camera operatively connected to the processors, data acquisition electronics, a flash lamp with power supply/trigger unit, a computer interfaced to these units for controlling flash triggering and data acquisition, and a test object with attached foil and tape as used in the measurement process.
Method of calculating image contrast evolution with known ROI temperatures and pixel intensities
The apparatus measures the measurement and reference ROI temperatures and reflection temperature, calculates the camera constant, and computes the image contrast evolution according to the presented formula.
Apparatus configured to convert temperature contrast evolution to image contrast evolution
An apparatus comprising one or more processors and memory units, configured to calculate measurement ROI temperature change ΔT, reference ROI temperature change ΔTref, reflection temperature change ΔTrefl, calculate the temperature contrast evolution Cl, and convert the temperature contrast evolution to image contrast evolution CWl using a specified equation.
Expanded apparatus integrating IR camera and related components for temperature-based measurement
The apparatus further includes an IR camera, data acquisition electronics, flash lamp with power supply/trigger unit, computer, and attachment of foil and tape to the object's surface to facilitate measurement.
Calculation of temperature contrast evolution from pixel intensities and reflection temperature
The apparatus calculates temperature contrast evolution by measuring pixel intensities at measurement, reference, and tape ROIs, measuring reflection temperature, and computing based on the specified equation.
The independent claims cover apparatuses equipped with processors and memory that perform calculations of temperature and reflection changes, image and temperature contrast evolutions, and conversions between image contrast evolution and temperature contrast evolution, incorporating IR cameras and associated hardware, and utilizing mathematical formulas to achieve accurate conversions and measurements in infrared flash thermography.
Stated Advantages
Improved accuracy in converting image contrast to temperature contrast by accounting for emissivity values less than one and reflection temperature changes.
Ability to assess emissivity of the test object in real-time using the foil-tape technique with the IR camera.
Capability to model afterglow heat flux and incorporate its influence on measurement, improving the accuracy of thermal data analysis.
Facilitates more accurate determination of surface temperature and anomaly characterization during infrared flash thermography inspections.
Documented Applications
Non-destructive evaluation (NDE) of thin materials such as laminated or bonded composites, particularly in aerospace applications.
Inspection for delamination-like anomalies and other defects such as surface cracks using infrared flash thermography imaging.
Processing and analyzing infrared thermography data for characterization of anomalies in test objects using IR cameras and associated flash thermography equipment.
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