Arao Kamoi

Experimental study on the effect of environmental fluctuations affecting thermal images of infrared radiometer

Infrared radiometer IR has been recently used as a remote sensing instrumentation system in various fields of industries. The IR displays the radiant energy distribution of the material to be measured as a 2D thermal image, and measures its radiation temperature and emissivity which are influenced by the environmental factors. As to applications of IR such as surface and internal defects of construction structure, existence of underground object and so on, it has been frequently experienced that the thermal images on a CRT display are fluctuating and those true temperatures cannot be measured correctly. This phenomenon is considered to be due to fluctuations of the meteorological and environmental factors, mainly influenced by irradiance (solar injection flux), wind velocity, atmospheric temperature, and so on. Our experimental study clarifies the correlation between variance of the thermal images of the CRT display and fluctuations of the above-mentioned environmental factors by analyzing the environmental factors and their power spectrum density as a function of frequency.

Study on Detection Limit of Buried Defects in Concrete Structures by Using Infrared Thermography

In Japan it happens that concrete parts suddenly collapse to create obstacles to the traffic in tunnels, on highways and bridges. Thus, the safety issue has become a serious social problem. Therefore, the detection of hidden defects in concrete building constructions in order to prevent an accidental damage is the important application area for nondestructive testing (NDT) techniques. Until now, the inspection is typically performed by using a hammer that is subjective and takes too much time. Infrared thermography is a promising NDT technique that might help in the fast detection of invisible (hidden) defects. Transient, or active, thermal NDT requires external thermal stimulation of the objects under test by warming up or cooling down the object surface. However, low-power and long heating is significantly affected by environmental conditions. Recent Japanese research in this area has been rather qualitative, i.e. without putting the accent on evaluating parameters of hidden defects. In this study, the experimental results are modeled and processed by using the thermal NDT software package developed at the Tomsk Institute of Introscopy. This has allowed not only optimizing test parameters but also obtaining reasonable estimates of defect parameters for air-filled voids and inclusions in concrete. It is shown that MRTD values measured by ourselves for the first time are of a little help while evaluating detection limit. Introduction Endurance and failure of concrete construction have recently become a social problem, because some accidents related to falling down of surface concrete blocks happened in the tunnel of New Tokaido Line and the girders of high way road. Ultrasonics and hammer sound as conventional inspection means have been tried and showed a low effectiveness. Infrared thermography has been recently recognized to be an effective NDT means in these fields [1]. This research is devoted to the analysis of detection limits while detecting air voids in mortar by applying external heating and monitoring temperature by means of an infrared camera. Most accidents, such as above-mentioned, occurred because defects of different natures were undetected in concrete structures during regular inspections (inclusions and cavities, as well as concrete degradations caused by salt attacks on a sea-side). These phenomena result in accidents and hazards with injury or death. Therefore, it is strongly expected to protect progressing degradation of concrete surface and to establish fast inspection, evaluation and maintenance technologies in order to realize a possible long life of concrete constructions. The inspection methods, except infrared thermography, are not suitable in detecting internal defects on-site for a short time, because sensors should be directly contacted to concrete surface and inspected areas are comparatively small. Infrared thermography is a noncontact technique due to remote sensing of radiation energy from concrete surface, allowing the visualization of concrete surface temperature as two-dimensional thermograms. The review of papers published in Japan from 1992 to 2002 on the inspection of internal defects in concrete parts Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1549-1555 doi:10.4028/www.scientific.net/KEM.270-273.1549

Studying the inspection limits in detecting buried objects by using infrared thermography

In Japan it happens that building parts made of concrete suddenly collapse to create obstacles to the traffic in tunnels, on highways and bridges. Thus, the safety issue has become a serious social problem. Therefore, the detection of hidden defects in concrete building constructions in order to prevent an accidental damage is the important application area for nondestructive testing (NDT) techniques. Until now, the inspection is typically performed by using a hammer that is subjective and takes too much time. Infrared thermography is a promising NDT technique that might help in the fast detection of invisible (hidden) defects. Transient, or active, thermal NDT requires external thermal stimulation of the defects under test by warming up or cooling down the defect surface. However, low-power and long heating is significantly affected by environmental conditions. Recent Japanese research in this area has been rather qualitative, i.e. without putting the accent on evaluating parameters of hidden defects. In this study, the experimental results are modeled and processed by using the thermal NDT package developed at the Tomsk Institute of Introscopy. This has allowed not only optimizing test parameters but also obtaining reasonable estimates of defect parameters for air-filled voids and inclusions in concrete. It is shown that MRTD values experimented by us are of a little help while evaluating detection limits.

Evaluation methods of NETD and MRTD for IR camera by using FLIR collimator

An application of infrared radiometer or IR camera has been widely spread in many industries for these twenty years, because of its convenience to use, wide measuring range by remote sensing, and visual survey due to thermal image. In this IR method it is very useful to detect invisible surface and internal flaws. Conventional IR makers are accustomed to use NETD as the resolution characteristics of IR camera, but general customers using IR camera cannot evaluate the minimum detectable size of measuring object, if they cannot evaluate MRTD. The study of the quantitative evaluation to clarify the relation between NETD and MRTD is very little. This paper represents evaluation methods of NETD and MRTD, and their quantitative relation by using collimator FLIR testing.

Dynamic Performance and Analysis of Moving Human Body

A visual digital recorder system (DVR) is widely used to visualize and analyze the dynamic image of moving body. The simultaneous instrumentation system of the DVR and infrared radiometer (IR) was applied to study two-dimensional moving images of the human body under walking and Gymnastic training. Dynamic behaviors of human body segments like location velocity and force are measured and analyzed by DVR, IR and the personal computer. Single-and multi-flash imaging methods of the human body were visualized and evaluated by using the multi flash motion recorder. Lastly, a fluctuation performance of the moving human body was quantitatively obtained and expressed in form of frequency, power spectrum density and coherence coefficient

Simultaneous visualization study on dynamic motion and temperature in moving bodies by means of infrared radiometer

In the field of dynamic engineering and biomechanics, the digital video recorder (DVR) is widely applied to visualize two- and three-dimensional images of moving machineries and human beings using several visual markers on the body surface. On the other hand, high-speed infrared radiometers (IR) are often used to visualize and analyze the dynamic image of moving body as well as their temperature distributions. IR radiometric systems are mainly applied to detect external and internal flaws of dynamic components and etiological causes of human beings in the field of industry and medicine, as remote-sensing non-destructive and diagnostic methods. Simultaneous visual studies of dynamic motion and temperature distribution of the moving body are very little to apply industrial and biological engineering systems. Quantitative analysis using the high-speed IR system was carried out to visualize and motion and thermal images of the moving bodies simultaneously. In this study, the high-speed IR system measures the dynamic and thermal images of the moving bodies using passive and artificial thermal markers and friction marks of the moving interface boundary. Dynamic motion characteristics of measured images by digital video recorder DVR and IR were quantitatively compared. Characteristics of single- and multi-flash imaging methods were measured and analyzed using the triggered motion coder. The IR radiometric systems are quite useful in the visualization and analysis of the motion and thermal distribution of the moving mechanical components, human bodies and their supporting components. These characteristics are well related to motion physiology, human welfare, health management etc.

Minimum radiation temperature difference and detection limit of flaws by means of an infrared radiometer

The infrared detection method has been carried out to detect the invisible flaw existing in a medium by observing a transient phase difference of a radiation temperature difference of deterioration parts and invisible flaws using the infrared radiometer. In order to evaluate the detection limit of the flaw using the infrared radiometer, it is important to confirm resolution characteristics of the radiometer like noise equivalent temperature difference NETD, minimum detectable temperature difference MDTD and minimum resolvable temperature difference MRTD under jurisdiction of ASTM, JIS and so on. However, the detection limit of the flaw displayed in the CRT of the radiometer is determined by the function of those values and surface radiation characteristics like emissivity, reflectivity and their spatial variance of the material and flaws used. The paper represents experimental and numerical results on the relation between the detection limit of the flaw and resolution characteristics of the radiometer itself.