Fluoride-type IR windows have good transmittance in the mid-wave IR band (3 to 5 micrometers). But, their transmittance drops rapidly in the long wave IR band (8 to 12 micrometers). Many low-cost plastic IR windows are also spectral in nature. Thermographers who measure the bandpass transmittance of these windows with their IR cameras may be in for a surprise or erroneous results when the IR window or the target temperature changes. Previous work, Proc. InfraMation 2004, indicates this is not a serious problem for certain target temperature ranges. This paper expands on the model to include effects of IR window thickness, IR window temperature changes and wider target temperatures. If you use low-cost IR windows, you need to know the results of this study.

This paper presents a thermal measurement system based on a Silicon image sensor camera operating in the Near Infrared spectral band (0.7-1.1 μm). The goal of the study is to develop a low-cost imaging system which provides an accurate measurement of temperature. A radiometric model is proposed to characterize the camera response by using physical parameters considering the specific spectral band used. After a calibration procedure of the model, measurements of black body temperatures ranging from 300 to 1000°C has been performed. The Noise Equivalent Temperature Difference (NETD) is lower than ± 0.18°C at a black body temperature of 600°C. Accurate measurements are provided over the whole temperature range by introducing an automatic exposure time control. The exposure time is adjusted for each frame along the evolution of temperature in order to optimize the temperature sensitivity and the signal-to-noise ratio. The paper also describes the conversion process of the apparent black body temperature to the real temperature of the observed object using its emissivity and surface geometry. The overall method is depicted and the influence of each parameter is analyzed by computing the resulting temperature uncertainty. Finally, preliminary experimental results are presented for monitoring real temperature of moulds in a Super Forming Process (SPF).

Radiometric infrared camera systems are most often used to characterize the IR signature of targets (often an aircraft or rocket) through significant air paths that reduce the received signal. Tactical targets can be imaged at standoff distances up to 1000km or more, but there are many cases where the target is within 1km range, as is the case with a close-in flyby at a test range. This paper compares experimental radiometric data to a theoretical model of the atmosphere. The radiometric data was collected in the 3-5 micron band using an indium antimonide staring-array camera and long focal length lens combined with radiometric analysis software. The system was calibrated to measure target radiances, but can also be used to estimate target temperatures in cases where the in-band target emissivity is well understood. The radiometric data are compared to a model built on MODTRAN code, with conclusions about the attenuation introduced by the atmosphere for standard medium-range imaging systems in “typical” observing conditions.

The idea of combining multiple image modalities to provide a single, enhanced picture offering added value to the observer or processor is well established, but the technology to realise it is somewhat less mature. In the past few years computing power has advanced sufficiently to finally enable affordable, real-time image fusion systems to become a reality and the field has started to move out of the research laboratories and into real products. Although algorithmic techniques for fusing images are now well known and understood, challenges remain with regard to exploiting different sensor modalities, robustness to environmental and operational conditions and proving performance benefit, to name but a few. This paper provides a broad review of the field of image fusion, from initial research published to the latest technology being developed and systems being deployed. Particular emphasis is placed on image fusion developments that have been made for the military community, which were mainly designed to exploit low light devices and thermal imagers. Wider applications of image fusion are also considered as well as all of the main technologies required to produce real-time image fusion systems. A summary of current and near-term products is given, as well as the latest research trends and end-user analyses reported to date.

Due to the modern advent of near ubiquitous accessibility to rapid international transportation the epidemiologic trends of highly communicable diseases can be devastating. With the recent emergence of diseases matching this pattern, such as Severe Acute Respiratory Syndrome (SARS), an area of overt concern has been the transmission of infection through respiratory droplets. Approved facemasks are typically effective physical barriers for preventing the spread of viruses through droplets, but breaches in a mask’s integrity can lead to an elevated risk of exposure and subsequent infection. Quality control mechanisms in place during the manufacturing process insure that masks are defect free when leaving the factory, but there remains little to detect damage caused by transportation or during usage. A system that could monitor masks in real-time while they were in use would facilitate a more secure environment for treatment and screening. To fulfill this necessity, we have devised a touchless method to detect mask breaches in real-time by utilizing the emissive properties of the mask in the thermal infrared spectrum. Specifically, we use a specialized thermal imaging system to detect minute air leakage in masks based on the principles of heat transfer and thermodynamics. The advantage of this passive modality is that thermal imaging does not require contact with the subject and can provide instant visualization and analysis. These capabilities can prove invaluable for protecting personnel in scenarios with elevated levels of transmission risk such as hospital clinics, border check points, and airports.

Equinox Corporation has developed two new video board products for real-time image fusion of visible (or intensified visible/near-infrared) and thermal (emissive) infrared video. These products can provide unique capabilities to the dismounted soldier, maritime/naval operations and Unmanned Aerial Vehicles (UAVs) with low-power, lightweight, compact and inexpensive FPGA video fusion hardware. For several years Equinox Corporation has been studying and developing image fusion methodologies using the complementary modalities of the visible and thermal infrared wavebands including applications to face recognition, tracking, sensor development and fused image visualization. The video board products incorporate Equinox's proprietary image fusion algorithms into an FPGA architecture with embedded programmable capability. Currently included are (1) user interactive image fusion algorithms that go significantly beyond standard "A+B" fusion providing an intuitive color visualization invariant to distracting illumination changes, (2) generalized image co-registration to compensate for parallax, scale and rotation differences between visible/intensified and thermal IR, as well as non-linear optical and display distortion, and (3) automatic gain control (AGC) for dynamic range adaptation.

The MWIR imaging systems developed by L-3 Communications Cincinnati Electronics (L-3 CE) include several video processing algorithms designed to provide enhanced imagery that meets a variety of military and other application requirements. When IR imaging systems are confronted with varying IR conditions, video processing algorithms are designed and selected to optimize human interpretation of specific scene details. The Visual Difference Predictor model has been used and a derived Image Enhancement Score has been developed to provide an objective metric to evaluate the effects of processing algorithms on imagery. Comparing the Image Enhancement Score of the processed image gives an objective measure of the success of the video processing algorithm being evaluated. This paper will describe selected algorithms in the L-3 CE Video Processing Suite, evaluate them against several test scenes and present associated Image Enhancement Scores. These will include a novel local contrast enhancement, general sharpening, and display mapping algorithms. Finally, the direction of ongoing and future efforts in Video Processing Suite development will be discussed.

In order to investigate temperatures reached during orthogonal metal cutting, a novel approach for measuring temperatures at the tool-chip interface has been developed based on high-speed thermography. A thermal infrared camera and a visible camera combined through a dichroic beam splitter form the basis for a synchronized visible and infrared imaging system. Pairing the infrared camera with a higher speed visible camera allows for assessment of thermal images with aberrant chip flow or an obstructed view of the tool/chip interface. This feature facilitates the use of the apparatus in machining environments where machining chips or other debris fly about. The measurement setup also includes a force dynamometer, custom timing circuitry, and a high-speed digital oscilloscope to enable timing of frames together with force measurements so that analysis of the infrared images can be compared against the energy levels measured through the cutting forces. The resulting infrared images were converted to radiance temperatures through comparison to a NIST calibrated blackbody. Emissivity was measured by thermally imaging the machining chips heated to known temperatures. Machining experiments were performed at various cutting speeds and at two different infrared wavelengths. Analysis of these experiments gives insight into the relationships between emissivity, temperature, surface condition, infrared wavelength and motion blur. The analysis shows that using the visible, thermal and force data together is a significant improvement over any of these alone. These insights lead to practical guidance for use of infrared imaging systems to image rapidly moving objects.

This paper describes the methodology that aims at detecting tube temperatures and diagnosis of heating medium in presence of visible and invisible flames, by means of sequences of the narrowband images stored during steady position of the applied camera. The main special feature of elaborated techniques is the dynamic spectrally matched IR thermography, which bases on forming single images that consist of pixels of chosen statistical value, minimum and maximum, noted during adequately long sequence of thermograms with total independence to the moment of their capture. Arrays of these data can be used directly, or as inputs to other artificial images. In this way, additive or suppressed interferences of fluctuating character could be minimalized or exhibited, depending on the type of investigations. By the use of properly chosen optical filters and algorithm, the elaborated method offers a new possibilities to test temperature problems other than more reliable tube temperature measurements, as for example study of heating medium features, symmetry, etc.

Infrared cameras are often used to capture high-speed digital video of scenes with enormous ranges in in-band brightness. A simple example of this is a rocket launch, a scene which can consist of a cold rocket hardbody and an extremely hot exhaust plume. It can be next to impossible to fully span a scene like this with the brightness dynamic range of an infrared camera (typically ~12-14 bits) at a single exposure value. The brightest or hottest parts of the image will often be saturated, while at the same time the darkest or coldest parts of the scene may be buried in the noise floor of the camera and appear black in the image. Varying the exposure by adjusting the camera to an optimal shutter speed or integration time is necessary to maximize the useful information recorded by the camera. Sometimes, however, a single integration time is not enough to fully encompass a scene’s brightness (temperature) variations. The technique of superframing gets around this problem by exploiting the capabilities of high frame-rate IR cameras. The technique involves cycling a camera through a set of integration times on a frame-by-frame basis, then combines the resulting “subframes” into single “superframes” with greatly extended dynamic ranges. If the frame rate is sufficiently high, the scene will not change appreciably from one subframe to the next. The technique and some sample data are described in this paper.

Process heaters are a critical component in the refining of crude oil. Traditional means of monitoring these high temperature vessels have frequently been more art than science, often relying on highly subjective analyses and/or frequently inaccurate thermocouple data. By utilizing an imaging radiometer specifically designed for heater inspections, valuable performance information can be obtained for operating heaters. In the hands of a knowledgeable engineering team, accurate infrared data can be utilized to significantly increase heater throughput while helping to ensure safe operation of the heater. This paper discusses the use of infrared thermography for online monitoring of operating crude heaters and the special challenges associated with this application.

This paper describes a methodology that aims to detect and diagnosis faults in lightning arresters, using the thermovision technique. Thermovision is a non-destructive technique used in diverse services of maintenance, having the advantage not to demand the disconnection of the equipment under inspection. It uses a set of neuro-fuzzy networks to achieve the lightning arresters fault classification. The methodology also uses a digital image processing algorithm based on the Watershed Transform in order to get the segmentation of the lightning arresters. This procedure enables the automatic search of the maximum and minimum temperature on the lightning arresters. These variables are necessary to generate the diagnosis. By appling the methodology is possible to classify lightning arresters operative condition in: faulty, normal, light, suspicious and faulty. The computacional system generated by the proposed methodology train its neuro-fuzzy network by using a historical thermovision data. During the train phase, a heuristic is proposed in order to set the number of networks in the diagnosis system. This system was validated using a database provided by the Eletric Energy Research Center, with a hundreds of different faulty scenarios. The validation error of the set of neuro-fuzzy and the automatic digital thermovision imagem processing was about 10 percent. The diagnosis system described has been sucessefully used by Eletric Energy Research Center as an auxiliar tool for lightning arresters fault diagnosis.

Furnas Centrais Elétricas S.A is one of the greatest companies of the Brazilian electric power sector and a pioneer in using infrared thermography. In the early 70s, the maintenance policy used was a centralized approach, with only one inspection team to cover all the company’s facilities. In the early 90s, FURNAS decided to decentralize the thermography inspections creating several inspection teams. This new maintenance policy presented several advantages when compared to the previous one. However the credibility of the results obtained with the thermal inspection was frequently being questioned, in part due to the lack of a detailed planning to carry out the transition from the centralized inspection to the decentralized one. In some areas of the company it was suggested the inactivation of the thermography. This paper presents the experience of FURNAS with these different maintenance policies and details the procedures which have been taken that nowadays the infrared thermal inspection has become one of the most important techniques of predictive maintenance in the company.

The UK Home Energy Conservation Act puts a duty on local authorities to develop strategies to improve energy efficiency in all public and private sector housing in order to tackle fuel poverty and reduce carbon dioxide emissions. The City of Nottingham, UK turned to aerial Thermal InfraRed Thermography (TIRT) to try and identify households where energy savings can be made. In this paper, existing literature is reviewed to explain the limitations of aerial TIRT for energy conservation in the built environment and define the techniques required to overcome them. This includes the range of suitable meteorological conditions at the time of the survey, the use of ground truth data, the need to account for all radiation paths and losses when calculating roof surface temperature and the assumptions that must be made when calculating insulation levels. Atmospheric calibration, roof surface emissivity and sky view factor must also be determined by some means and approaches to these problems are reviewed from the wider literature. Error analysis and benchmarking are important if the technique is to be validated and these are discussed with reference to the literature. A methodology for determining the thickness of loft insulation for residential buildings in the city of Nottingham, UK using aerial TIRT data within a GIS software environment is proposed.

A great development of technologies for the detection of buried objects took place in the last years. Applications in archeology, finding of pipe lines and others were important, but most attention was paid in humanitarian detection of land mines and unexploded ordnances. Among these technologies, thermography is one of the most useful techniques and has been applied concurrent with other ones (Ground Penetrating Radar, Electromagnetic Induction, etc.) We have made several experiments to obtain thermographic images of buried objects in the middle and far infrared, in laboratory and in field, and in different types of terrain: naked ground, ground covered with grass and sand. We employed, as warming methods, natural sun radiation and blowing of warm air or halogen lamps. We have used metallic and dielectric objects of different sizes and shapes so as to recognize them by their characteristics. The acquired images were improved using noise reduction and image enhancement techniques. In this work we present the thermographic images obtained. All measurements were made at short distance, less than 100 cm, as the objective of our work is to develop a thermographic imaging system for the detection of buried objects to be installed in an autonomous ground robot.

Many applications of IRT on buildings require active approach. The solicitation has to be properly calculated, and the application has to take in account the optical characteristics of the surface and its thermal properties. In fact, non-homogeneities of the surface definitively affect the absorbance and reflectance of materials, as shown in literature. Therefore, in case of different colors like artistic paintings, dark stains and salts deposition a convection heating results more effective for IRT inspection, because it does not stimulate different localized absorption due to the colors. Using fan coil heaters, major difficulty is to obtain an even heating on the wall under inspection. The laboratory tests permitted to verify that the strength of rising warm air is higher than the one due to the heater ventilation. As a consequence, the effects of heating on the wall start from the upper part and decrease in a non-proportional way to the bottom. On the other side, thermal flux from a heater changes direction according to the geometry of the room, ambient conditions (initial temperature of the air, openings, etc), technical characteristics of the heater (power, speed of the fan, shape, etc) and its location (orientation, elevation, distance from the surface under investigation, etc). In addition, the increase of air temperature does not directly correspond to the increase of the surface temperature. The paper shows the characterization of a convective heating source, by laboratory measurements; to map the distribution of heat in time, the 14.000-26.000 kcal/h heater flux was measured following a 3D grid, by anemometers, probes, and IR Thermography.

Approximately 5 billion dollars in US revenue was lost in 2003 due to open area fires. In addition many lives are lost annually. Early detection of open area fires is typically performed by manned observatories, random reporting and aerial surveillance. Optical IR flame detectors have been developed previously. They typically have experienced high false alarms and low flame detection sensitivity due to interference from solar and other causes. Recently a combination of IR detectors has been used in a two or three color mode to reduce false alarms from solar, or background sources. A combination of ultra-violet C (UVC) and near infra-red (NIR) detectors has also been developed recently for flame discrimination. Relatively solar-blind basic detectors are now available but typically detect at only a few tens of meters at ~ 1 square meter fuel flame. We quantify the range and solar issues for IR and visible detectors and qualitatively define UV sensor requirements in terms of the mode of operation, collection area issues and flame signal output by combustion photochemistry. We describe innovative flame signal collection optics for multiple wavelengths using UV and IR as low false alarm detection of open area fires at long range (8-10 km/m²) in daylight (or darkness). A circular array detector and UV-IR reflective and refractive devices including cylindrical or toroidal lens elements for the IR are described. The dispersion in a refractive cylindrical IR lens characterizes the fire and allows a stationary line or circle generator to locate the direction and different flame IR “colors” from a wide FOV. The line generator will produce spots along the line corresponding to the fire which can be discriminated with a linear detector. We demonstrate prototype autonomous sensors with RF digital reporting from various sites.

Air leakage occurs in a variety of different ways through all types of exterior walls. In cold or warm climates, air leakage is accompanied with moisture transport. This moisture transport when migrating through dew point temperatures, leads to moisture accumulation within wall assemblies. This moisture accumulation may result in premature deterioration and mould formation given appropriate prolonged environmental conditions. Commissioning of air barrier assemblies using infrared thermography is an effective means of locating areas of air leakage defects. Since the environmental conditions that commissioning or building condition inspections are carried out vary considerably, the resultant air leakage thermal patterns on wall surfaces vary accordingly. This paper will outline the various types of thermal patterns created by both positive and negative building pressures during exterior inspection of various types of masonry clad buildings. These thermal patterns can be extrapolated to similar naturally occurring air leakage thermal patterns created by wind, stack effect and lack of existing mechanical system pressurization. This paper will outline the variable thermal pattern conditions created by cavity wall construction in addition to homogeneous solid wall construction and face seal type assemblies.

Thermography has been used in Finland in building survey from the late 70s. The service has been provided by consultants, whose background is varied. When technology and devices have improved and the prices have increased, more and more doers have come into the market. At the same time, building developers and contractors have begun to use thermography for quality control in new building. Thermography has also been used in renovation planning. The problem is, that there are no procedures for building thermography, no guidelines to order the thermography services, no instructions how to scan, how to report and most important -- how to interpret the results. That fact has caused a lot of problems and also damaged the reputation and reliability of the method. In this year 2004 the various organizations in building trade launched a pilot project to certificate building thermographers. The procedure is divided into two parts: Part 1 is Level I (the basis of thermography) and Part II (divided into two periods) thermography applications of buildings, including also information on building physics, heat and mass transfer and structures. Both parts will take a week, two weeks in total with the examinations. The procedure follows moisture measurement procedure -- certification of building moisture measurements started a couple of years ago. In the paper the procedure, problems and the future plans are introduced. The following big issue is to develop and improve the interpretation procedure for reporting the results of thermography.

For years the pest Management Professional has relied on visual and manual inspections to locate insect pest infestations. As building materials have improved, the ability to locate pest problems has become more difficult since building materials are often able to mask the existence of pest infestation. Additionally, these improved building materials have contributed to the pest problem by providing a convenient food and nesting source. Within the past five years, the Pest Management Industry has become aware that IR thermography can aid in the detection of pest infestation by detecting evidence of latent moisture within structures. This paper discusses the use of thermal imaging to detect thermal patterns associated with insect infestation, verification of data and special challenges associated with the inspection process.

Using a previously developed and validated modeling approach for FEA-based heat transfer, the impact of the amount of water and its location in a wall or similar structure on the thermal signature of the surface is examined. The results are used to determine whether or under what conditions the IR results can be used to determine the amount of water and its depth in the structure. The amount and location of the water has significant effects on the thermal signature of the wall. This approach can also be used to examine the impact of the depth of a delamination or other subsurface features on the thermal signature with the potential for providing guidance to applying IR for quantification of these features as well.

The objectives of this research were to (1) understand the impact of vibration on electronic components under ultrasound excitation; (2) model the thermal profile presented under vibration stress; and (3) predict stress level given a thermal profile of an electronic component. Research tasks included: (1) retrofit of current ultrasonic/infrared nondestructive testing system with sensory devices for temperature readings; (2) design of software tool to process images acquired from the ultrasonic/infrared system; (3) developing hypotheses and conducting experiments; and (4) modeling and evaluation of electronic vibration stress levels using a neural network model. Results suggest that (1) an ultrasonic/infrared system can be used to mimic short burst high vibration loads for electronics components; (2) temperature readings for electronic components under vibration stress are consistent and repeatable; (3) as stress load and excitation time increase, temperature differences also increase; (4) components that are subjected to a relatively high pre-stress load, followed by a normal operating load, have a higher heating rate and lower cooling rate. These findings are based on grayscale changes in images captured during experimentation. Discriminating variables and a neural network model were designed to predict stress levels given temperature and/or grayscale readings. Preliminary results suggest a 15.3% error when using grayscale change rate and 12.8% error when using average heating rate within the neural network model. Data were obtained from a high stress point (the corner) of the chip.

Sonic IR is an emerging, thermal-based, nondestructive evaluation (NDE) technique. Typically a short burst of high power acoustical energy is injected into an object being studied and certain types of defects heat up and is detected using a thermal imaging camera. This inspection technique is very fast, lasting only a few seconds for total inspection time. However due to many uncertainties in the inspection process it has yet to be adopted widely by industry. There are many unknown parameters governing sonic IR, which need to be understood before it becomes a widely used NDE technique. This paper shows that under certain conditions cracks can grow when subjected to the sonic IR technique. We also examine the effects of various experimental parameters on the technique.

In the case of thermo-inductive probing the material is heated by HF-induced eddy currents and the emission from the material surface is detected by an infrared camera. Anomalies in the surface temperature correspond to in-homogeneities in the material. Due to the high excitation frequency (200 kHz) and the magnetic properties of the material, the penetration depth of the current is very small (about 0.03 mm). Therefore the eddy current 'flows around' surface cracks with a depth of 0.1-1 mm. This causes a higher current density and higher temperature around the failures, which are made visible by the infrared camera. Experiments have been carried out on steel wires with a diameter of 4.5-10 mm and with longitudinal surface cracks with a depth of 0.1-0.2 mm. Due to the high heat conductivity of the material, the temperature difference diminishes very quickly. Therefore short heating pulses with duration of 0.1-0.5 sec have been applied. The measurement result shows, that the thermo-inductive method is well suited to detect such shallow flaws. An analytical model has been derived, to calculate the temperature distribution in the wire and around the failure. The model also shows the dependence of the temperature distribution on the parameters of the experiments, as e.g. the length of the heating pulse, which helps to optimize the measurement setup. Additionally, finite element simulations have been carried out. The results of the model-calculations and the simulations are successfully compared with the experimental results.

The study deals with the long-term reliability of a high precision pressure sensor using bellows mainly made of electroplated Ni. Bellows are expected to stay in service for many decades. Their high cycle fatigue behavior has to be known to assess the probability of airtightness loss. A specific high cycle fatigue setup, put in a resonant machine that is displacement-controlled, has been designed. An infrared thermographic technique is used to determine the mean fatigue limit of bellows. Increases in the mean temperature of the bellows with the displacement range are monitored. Several authors empirically relate the mean fatigue limit of a flat specimen to a rapid temperature change. A similar analysis is performed in the present case by using the bellows mean temperature. Finite element computations allow us to estimate a mean fatigue stress threshold for electroplated Ni. This result is compared with those obtained mechanically in a Woehler diagram.

Utilizing the Thermal Infrared (TIR) imaging technology, the transient process of solids (Three kinds of rocks and one kind of PMMA) impacted by free-falling steel balls are monitored with an infrared camera. It is discovered that: (1) as for rock materials, the increments of IR temperature (both the maximum and average, i.e., ΔT_max and ΔT_avr) are all linear related to the impacting height, the difference are the statistical correlation coefficients (R): relatively homogeneous rock (marble, R=0.93~0.95); non-homogeneous rocks (granite: R=0.88~0.92; gabbro: R=0.80~0.84); while for PMMA, there exists a critical height (h≈5m), within this height, ΔT_max is quadratic related and ΔT_avr is linear related to the impacting height, and when above this critical height, both ΔT_max and ΔT_avr are linear related, comparison to rocks, the statistical correlation coefficients are somewhat higher (R=0.94~0.96); (2) the amplitude of IR temperature increments are different, it is somewhat less of IR temperature variations for relatively hard rocks (granite) than others (gabbro, marble and PMMA), for example, when impacted at a height of 2 meter with a standard ball (1 inch in diameter), the higher ΔT_max≈2~4K, while others are within 1K, and (3) it is verified that the parameters about the impaction could be well inversed qualitatively to quantitatively, not only the type of rocks can be identified exactly, but also the impacting height can be accurately estimated especially for the relatively homogenous materials, as for marble rock and PMMA, the relative mean errors of inversion are less than 11.3% and 6.2%, respectively.

IRT technique applications for the detection of the plasters defects in historic buildings are widely documented by scientific literature. Previous studies demonstrated the advantages of tomographic techniques to obtain quantitative results by IRT. With a quantitative approach, the dynamic measures of IRT, versus time and maximum value of thermal contrast, allows to locate the delamination and calculate its volume inside the thickness of the plaster. Nevertheless, effects are not prominent if compared with the ones caused by the interaction between surface and irradiation. Moreover these effects are lower than the noise due to the approximation of the spectral coefficient value. Authors already showed that the multispectral evaluation of the reflectance coefficients, in the range of visible and near IR, contributes to a proper evaluation of the thermograms shot on surfaces affected by chromatic alterations. In the study case, the evolution of the surface temperature in time allows to quantify the effects of spectral absorption (absorbance) in the thermograms. By comparing the thermograms to the maps of damages and intervention, it has been possible to correlate the materials and its state of conservation to the evolution of the thermal profile corresponding to each analyzed area.

At the conclusion of the Columbia Accident Investigation, one of the recommendations of the Columbia Accident Investigation Board (CAIB) was that NASA develop and implement an inspection plan for the Reinforced Carbon-Carbon (RCC) system components. To address these issues, a group of scientists and engineers at NASA Langley Research Center proposed the use of an IR camera to inspect the RCC. Any crack in an RCC panel changes the thermal resistance of the material in the direction perpendicular to the crack. The change in thermal resistance can be made visible by introducing a heat flow across the crack and using an IR camera to image the resulting surface temperature distribution. The temperature difference across the crack depends on the change in the thermal resistance, the length of the crack, the local thermal gradient, and the rate of radiation exchange with the environment. The current paper describes how the authors derived the minimum thermal gradient detectability limits for a through crack in an RCC panel. This paper will also show, through the use of a transient, 3-dimensional, finite element model, that these minimum gradients naturally exist on-orbit. The results from the finite element model showed that there exists sufficient thermal gradient to detect a crack on 96% of the RCC leading edge.

One of NASA’s Space Shuttle Return-to-Flight (RTF) efforts has been to develop thermography for the on-orbit inspection of the Reinforced Carbon Carbon (RCC) portion of the Orbiter Wing Leading Edge (WLE). This paper addresses the capability of thermography to detect cracks in RCC by using in-plane thermal gradients that naturally occur on-orbit. Crack damage, which can result from launch debris impact, is a detection challenge for other on-orbit sensors under consideration for RTF, such as the Intensified Television Camera and Laser Dynamic Range Imager. We studied various cracks in RCC, both natural and simulated, along with material characteristics, such as emissivity uniformity, in steady-state thermography. Severity of crack, such as those likely and unlikely to cause burn through were tested, both in-air and in-vacuum, and the goal of this procedure was to assure crew and vehicle safety during re-entry by identification and quantification of a damage condition while on-orbit. Expected thermal conditions are presented in typical shuttle orbits, and the expected damage signatures for each scenario are presented. Finally, through statistical signal detection, our results show that even at very low in-plane thermal gradients, we are able to detect damage at or below the threshold for fatality in the most critical sections of the WLE, with a confidence exceeding 1 in 10,000 probability of false negative.

Designed to fulfill a critical inspection need for the Space Shuttle Program, the Infrared On-orbit RCC Inspection System (IORIS) can detect crack and surface defects in the Reinforced Carbon-Carbon (RCC) sections of the Space Shuttle’s Thermal Protection System (TPS). IORIS performs this detection by taking advantage of the natural thermal gradients induced in the RCC by solar flux and thermal emission from the Earth. IORIS is a compact, low-mass, low-power solution (1.2cm3, 1.5kg, 5.0W) for TPS inspection that exceeds existing requirements for feature detection. Taking advantage of ground-based IR thermography techniques, IORIS provides the Space Shuttle program with a solution that can be accommodated by the existing inspection system. IORIS augments the visible and laser inspection systems and finds cracks that are not easily measurable by the other sensors, and thus fills a critical gap in the Space Shuttle’s inspection needs. Based on crack IR signature predictions and on-orbit gradient expectations, IORIS can achieve crack detection over approximately 96% of the wing-leading edge RCC (using multiple inspections in an orbit period). This paper discusses the on-orbit RCC inspection measurement concept and requirements, and then presents a detailed description of the IORIS design.

Thermographic inspection techniques fundamentally vary by method of heat deposition. Some systems use a short burst of energy from a flash lamp while others control the motion of a quartz lamp over the material. Both techniques have had a history of successful inspections on aircraft and boiler tubes, for example. Historically, the system used for inspections was determined by the thermographic equipment available to the researcher. This paper will compare the flash and line scan thermographic systems on Reinforced Carbon-Carbon. Reinforced Carbon-Carbon (RCC) is a brittle composite material that is found on the Space Shuttle’s nose section, wing leading edges, and chin panel. It is used to protect the orbiter’s aluminum frame from superheated air during flight. In the time since the Columbia accident, impact tests on RCC panels have been ongoing. Flash thermography has been successfully used to scan the impact site for delaminations. While the system has proven effective, it is not without limitations. A single scan yields only that section of material that is in the field of view of the infrared camera. Additionally, delaminations deep within the material may not be resolved as well as with quartz heating. A comparative study was conducted using a RCC panel with flat-bottom holes varying in diameter and depth. The panel was scanned with the Thermal Line Scanner, the Thermal Photocopier, and the Echotherm from Thermal Wave Imaging. Signal to noise ratios were calculated for the defects and used to compare the three systems. This paper will discuss the details of the study and show the results obtained from each of the three systems.

Thermal non-destructive testing (NDT) is commonly used for assessing aircraft structures. This research work evaluates the potential of pulsed -- transient thermography for locating fixtures beneath aircraft skins in order to facilitate accurate automated assembly operations. Representative aluminium and carbon fibre aircraft skin-fixture assemblies were modelled using thermal modelling software. The assemblies were also experimentally investigated with an integrated pulsed thermographic evaluation system, as well as using a custom built system incorporating a miniature un-cooled camera. Modelling showed that the presence of an air gap between skin and fixture significantly reduced the thermal contrast developed, especially in aluminium. Experimental results show that fixtures can be located to accuracies of 0.5 mm.

Pulsed Phase Thermography (PPT) is rapidly evolving as a solid NDT&E technique. Acquisition is accomplished in a similar way as in classical Pulsed Thermography, thermal data is processed afterward using a transformation algorithm, e.g. the Fourier Transform (FT), providing amplitude and phase delay data. The authors have recently presented an extended review on PPT theory, as well as a new inversion technique for depth retrieval using phase. Furthermore, an automatic defect depth retrieval algorithm had also been presented. Due to the Time-Frequency Duality of the discrete FT, PPT sampling and truncation parameters should be carefully selected to produce the desired frequency response. An interactive methodology for the optimal selection of these parameters has been proposed. Nevertheless, this is not always a simple task. On one hand, there exists stored data for which sampling and truncation was performed without considering the time-frequency relationship; and on the other hand, there is not always possible to produce the desired frequency output because of equipment limitations. In this paper, two situations are considered. First, two composites plates (CFRP and GFRP), for which adequate parameters have been used. In this case, we demonstrate that depth can be directly estimated from the diffusion length equation as is done by Lock-In Thermography. Secondly, an aluminum specimen that has been incorrectly sampled is considered. In this case, we propose the normalized diffusion length μ_n, and the normalized diameter D_n, to account for defect size variation.

Pulsed Phase Thermography (PPT) has been proven effective on depth retrieval of flat-bottomed holes in different materials such as plastics and aluminum. In PPT, amplitude and phase delay signatures are available following data acquisition (carried out in a similar way as in classical Pulsed Thermography), by applying a transformation algorithm such as the Fourier Transform (FT) on thermal profiles. The authors have recently presented an extended review on PPT theory, including a new inversion technique for depth retrieval by correlating the depth with the blind frequency f_b (frequency at which a defect produce enough phase contrast to be detected). An automatic defect depth retrieval algorithm had also been proposed, evidencing PPT capabilities as a practical inversion technique. In addition, the use of normalized parameters to account for defect size variation as well as depth retrieval from complex shape composites (GFRP and CFRP) are currently under investigation. In this paper, steel plates containing flat-bottomed holes at different depths (from 1 to 4.5 mm) are tested by quantitative PPT. Least squares regression results show excellent agreement between depth and the inverse square root blind frequency, which can be used for depth inversion. Experimental results on steel plates with simulated corrosion are presented as well. It is worth noting that results are improved by performing PPT on reconstructed (synthetic) rather than on raw thermal data.

In conventional flash thermography a brief pulse of light with a full width half maximum duration of 2-4 ms is applied to the surface of a solid sample and the surface temperature response is recorded with an infrared camera. In practice, the flash duration is typically fixed, and the amplitude is the only adjustable flash parameter. Flash amplitude is normally adjusted to provide maximum illumination of the sample surface without causing saturation of the camera detector array. However, more precise interrogation of the subsurface structure is obtained if the timing parameters of the flash excitation and the detector are carefully determined and controlled. In particular, limiting the pulse duration and the offset between the pulse and the detector integration time significantly increases correlation between modeled and experimental results during the early post-flash frames. Additionally, a new method is described to precisely detect the initiation and duration of the pulse for common high performance infrared cameras.

A soft material testing, as leather is more difficult than a rigid material one, especially for the variable shape. A complex processing is actually performed to accomplish the industry requirements and much more information about the internal structure is requested than simple visual inspection. Pulsed Phase Thermography is a suitable tool for a fast and reliable testing of such materials. A first step is the Non Destructive Testing devoted to the identification of hidden scratches. A more complex analysis is required to visualize the texture in depth, evaluating the quality of the final product. Thermal diffusivity and effusivity proven their usefulness to distinguish among different leather types. Experimental results on different specimens containing intentionally fabricated defects and normal samples are presented. The used experimental procedure is described. A mathematical model of the leather covered by a finishing layer has been applied to interpret experimental data.

Rolling Contact Fatigue (RCF) is one of the main issues that concern, at least initially, the head of the railway; progressively they can be of very high importance as they can propagate inside the material with the risk of damaging the railway. In this work, two different non-destructive techniques, infrared thermography (IRT) and fibre optics microscopy (FOM), were used in the inspection of railways for the tracing of defects and deterioration signs. In the first instance, two different approaches (dynamic and pulsed thermography) were used, whilst in the case of FOM, microscopic characterisation of the railway heads and classification of the deterioration -- damage on the railways according to the UIC (International Union of Railways) code, took place. Results from both techniques are presented and discussed.

In the thermoelastic stress analysis, stress distribution is measured by lock-in infrared thermography, which correlates temperature change due to the thermoelastic effect with reference loading signal. Loading signal from external source, such as load-cell, strain gage or displacement gage, is usually employed as a reference signal in the conventional lock-in technique. In this study, a self-reference lock-in infrared thermography was newly developed, in which a reference signal was constructed by using the same sequential data on thermoelastic temperature change. Temperature change in a region of interest was correlated with that in a remote area for reference signal construction. The lock-in algorithm based on the least squares method was employed for signal processing under random loading. It enabled us to measure the distribution of relative intensity of applied stress under random loading without using any external loading signal. Proposed self-reference lock-in thermography was applied for crack identification based on the detection of significant thermoelastic temperature change due to the singular stress field in the vicinity of crack tips. It was found that significant temperature change was observed at the crack tip in the self-reference lock-in thermal image, demonstrating the feasibility of the proposed technique.

Recent developments in infrared camera technology, testing methods and data processing algorithms have brought significant progress for high resolution spatial and temporal analysis of thermal radiation. Together with industry standard automation technology and specific infrared image data processing it became possible to non destructively inspect laser welded seams and other types of joints using heat flux analysis subsequent to active thermal excitation. High thermal diffusion coefficients of the usually metallic samples under test make the availability of high-speed infrared cameras as a key hardware component indispensable. Since high-speed infrared cameras with frame rates of at least 500 Hz have become available for commercial applications, non-destructive testing systems with a new class of performance were designed, manufactured, and implemented at industrial sites. Heat flux analysis as a new and robust method of non-destructive testing has been implemented for various types of equipment, ranging from off-line tools for laboratory use to automated robot based systems enabling fast and operator-free in-line inspection. Depending on environment, implementation surroundings, and geometry of objects to be inspected, different types of pulsed or continuous operating heat sources (e.g. flash light, laser, ...) are selected. Due to its outstanding industrial relevance some examples of non-destructive testing of laser welded seams in automobile manufacturing are shown.

Analysis of thermal data requires the processing of large amounts of temporal image data. The processing of the data for quantitative information can be time intensive especially out in the field where large areas are inspected resulting in numerous data sets. By applying a temporal compression technique, improved algorithm peformance can be obtained. In this study, analysis techniques are applied to compressed and non-compressed thermal data. A comparison is made based on computational speed and defect signal to noise.

Flash thermography is widely used to inspect Thermal Barrier Coatings (TBC) during manufacturing and maintenance for defects such as delamination or contamination. However, attempts to use thermography to quantify TBC thickness have been less successful. In conventional thermographic NDT applications, the sample surface is opaque to an incident light pulse, and highly emissive in the infrared. The situation is more complex in TBC's, as the coatings are translucent to visible light and near-IR radiation (including the IR component of the flash). Furthermore, TBC's are translucent to the mid-IR wavelengths at which many IR cameras operate. Thus, in the absolute worst case, the flash pulse does not heat the coating, and the camera does not see the coating. Although the latter problem can be mitigated by judicious choice of camera wavelength, it must also be recognized that both the heating and cooling mechanisms in a flash-heated TBC are different from the usual thermography model, where transit time of a heat pulse from the sample surface to a layer interface is an indicator of coating thickness. The resulting time sequence is processed using the Thermographic Signal Reconstruction to generate thickness maps which are accurate to an accuracy of a few percent of the actual coating thickness.

The paper contains new results obtained in detecting and evaluating water hidden in honeycomb panels of aircraft under exploitation. The accent is made on evaluating water content by using the ice-to-water phase transformation and visible size of temperature patterns in water sites.

A thermal, non-destructive evaluation (NDE) technique has been employed by ThermTech Services, Inc. in cooperation with NASA Langley Research Center that allows for quantitative measurements of wall thickness in steam boilers. By determining the thickness of the walls, one can easily determine how much thinning has occurred due to corrosion. This type of NDE can be applied to the inspection of wings and fuselages on aircraft and spaceflight vehicles including the shuttle. The NDE technique employs the linear movement of a heat source (lamp) and an infrared imager that is situated at a fixed distance behind the heat source. The instruments are aligned on a platform that moves up and down across the outer surface of a test sample. By analyzing the induced surface temperature variations, and processing images collected with the infrared imager, it can be determined where material loss of the tubes has occurred. After an image sequence has been collected, a line-by-line subtraction methodology is utilized to discard irrelevant information so that defects are displayed in a re-created image. The overall goal of this project is to provide a proof of concept for a portable, hand-operated thermographic line scanner that would provide an alternative to the existing mass- and power-intensive instrument that utilizes a cooled infrared imager. In this project, two different microbolometers are first analyzed using different metal- and carbon epoxy-based targets to determine which provides better resolution for detection of subsurface, manufactured defects. The feasibility of using uncooled bolometer technology to support the development of a portable instrument to conduct this type of NDE technique was proven.

To date, a full-scale solar sail has never flown in space. Furthermore, solar sail technology development represents a field that only recently has enjoyed significant support. The goal of this work is to contribute to the development of a low-mass ODS for solar sails that would include research and development in the areas of photogrammetry and thermography. The focus of this work was on the development of the thermography system. A measurement protocol was designed for obtaining accurate temperature measurements using thermal imaging when heat was applied to the membrane surface. Two main limitations were considered during the experimental process. The first is that conventional infrared detector arrays must be kept cool. To minimize the effect that an imager’s operating temperature would have on the ODS, a miniature, un-cooled microbolometer was used to acquire temperature measurements from the membrane surface. A second limitation is that a detector array cannot distinguish between emitted and reflected photons, thus presenting a significant problem if one cannot predict the reflected component or if the reflected component is significantly greater than the emitted. To address this limitation, spectral properties of the membrane, including reflectance and transmission, were analyzed using a Hemispherical Directional Reflectometer (HDR) to predict the effects that optical properties would have on sail membrane temperatures. A thermal modeling strategy was also developed. The results of this investigation are presented.

This paper is a slightly modified version the one presented orally at THERMOSENSE XXVI April 13 - 15 2004 SPIE [5405-46] Session 8: Research & Development. Many industrial applications exist for which, due to the lack of access or for other reasons, thermal images or thermometry measurements cannot be generated. This happens especially when the target is inside an enclosure and cannot be viewed, for safety -- process reasons, except through a window transparent to visible energy only. The traditional materials transparent to visible radiation ~380 nm - ~780 nm are not, in general, transparent to infrared radiation. It is clear there is a more specific exception in the NIR band. This lack of IR transmission in traditional glass/crystals has required the search for other alternatives in order to carry out measurements or generate images with instruments that work in the thermal bands (MWIR - LWIR) of the electromagnetic spectrum. This paper includes infrared windows basics and a study of attenuation with LWIR sensor of two windows two colors transmission (MWIR/LWIR) commonly installed in medium voltage electrical enclosures.