The requirement for lower cost infrared systems has led to interest in sensors based on linear pyroelectric array technology. Like all pyroelectric detectors, linear arrays are free from the constraints of temperature control, operating over the full military temperature range with minimal reduction in performance. Since most objects of interest have, or can be arranged to have, movement with respect to the observer, this motion is used to produce a 2-dimensional image rather than an optical scanning mechanism. Here we describe a linear pyroelectric array which is designed to have good thermal sensitivity, low microphony, low power consumption, and to be easy for the system designer to use without taking special measures. We also describe a sensor head system design which makes use of the features of the detector in order to achieve a good thermal sensitivity along with a practical, low cost sensor design.
This paper describes the principles of measurement and main features of operation of an infrared linescanner system developed by Sira Ltd for measurement in a refining process. The output from the unit is a thermographic picture of the electrolytic tank surfaces in which thermal anomalies appear as a darkening/linghtening of the picture detail.
The increasing use of fibre reinforced composite materials in structural components, mainly in the aircraft industry has induced manufacturers to acquire appropriate non destructive testing means. Then the necessity to manufacture with larger production rate and tighter quality control requires inspection techniques having higher speed and finer resolution with more accuracy and intelligence than the conventionnal one's used today, namely ultrasonics and X - radiography. A large assessment program has been carried out in order to demonstrate the applicability and reliability of infrared thermography as a method for the inspection of composite and bonded materials.The technique has been developed for an industrial utilization and to specify the systems required for its application. The developments undertaken and the results we have obtained in the final stage of the program are presented.
A computerized infrared (IR) imaging system is evaluated as a diagnostic tool for aerodynamic research by performing experimental tests in a subsonic wind tunnel. In particular, the IR technique is used to characterize the behaviour of the boundary layer on two wing models, having different cross-sections, by measuring the temperature distribution over their heated surfaces. The results show that IR thermography is capable of immediately yielding accurate information on the location and extent of the transition between laminar and turbulent flow and on the region of separation, for the whole boundary layer over the surface of a model wing.
The human body has a unique and sophisticated thermoregulation. It is one of the important processes, which enable man to function in a range of ambient conditions. The skin is a vital organ in this process, serving as an interface between the body and its immediate environment. Skin behaves as a near black body, with a high emissivity. The presence of hair is shown to an insulator, trapping the infra red emission from the scalp or skin surface. Man also needs protection in most climates, and uses clothing materials to insulate the body from direct heat loss. The warm air trapped between the body space and clothing creates a 'microclimate' which is subjectively adjustsed for comfort'.
A high resolution medical thermal imaging system using an 8 element SPRI1E detector is described. Image processing is by an Intellect 100 processor and is controlled by a DEC LSI 11/23 minicomputer. Image storage is with a 170 Mbyte winchester disc together with archival storage on 12 inch diameter optical discs having a capacity of 1 Gbyte per side. The system is currently being evaluated for use in physiology and medicine. Applications outlined include the potential of thermographic screening to identify genetic carriers in X-linked hypohidrotic ectodermal dysplasia (XED), detailed vas-cular perfusion studies in health and disease and the relation-ship between cutaneous blood flow, neurological peripheral function and skin surface temperature.
An attempt is made to show how Infrared Thermography may effectively aid in yielding realistic assessments of both hardware and human reliability parameters, such as failure/ error rates, corresponding to working conditions actually sensitive to and/or reflected in the existing thermal environment, which usually are not explicitly and specifically accounted for in current quantitative reliability and risk analyses. An analysis, emphasizing first principles and measurable phenomena, is made conducive to characterize specific functional relationships between the relevant thermal patterns and those reliability parameters which may lead to the actual assessment of the latter. The application of this analysis to fault/failure mode diagnosis, and both preventive maintenance and risk analysis is also addressed.
Infrared thermography is a useful method of recording skin temperature distributions. It can be shown that the thermal pattern of an individual is a complex function of surface topography, anatomy, blood perfusion in subcutaneous tissues, superficial vascularity and environmental temperature. A variety of physiological and pathological factors can also affect skin temperature. Three examples are illustrated: the scrotal varicocele, vascular changes associated with malignancy and the effect of large doses of ionizing radiation on the skin.
A very high sensitivity scanning radiometer has been developed for remote sensing in the 8-12 μ.m spectral region. The paper describes this system which, under computer control, can automatically monitor the thermal emissions from one point or many points within a preselected field of view. The thermal data is displayed either digitally or in the form of graphs or as colour coded thermal maps of the area under inspection. This instrument offers a highly versatile scanning system combined with a thermal resolution much greater than usually available from current thermographic systems down to 1 mK. Furthermore, in addition to point, line and area scans, temperature vs time plots of single points may be produced. Many digitally recorded scans may be stored and quickly recalled for examination. The range of potential uses is wide and it is envisaged that the instrument would be particularly valuable in those applications requiring up to 100x the resolution of typical thermographic systems.
A multi- channel spectroradiometer has been developed by Sira Ltd for the study of rapidly varying events in the near infrared. The instrument is being used in the examination of gun flashes, rocket motor exhaust efflux analysis and ordnance or pyrotechnic flash studies. The spectral range of about 1.4 to 5.2 microns is covered in two bands with the first order dispersion from a pair of ruled blazed gratings being imaged onto a pair of detector arrays. Data may be logged at a rate of 1000 complete spectra per second.
This paper discusses the advantages that can be achieved by replacing traditional filter wheel constructions with integrated multichannel detectors in infrared process analyzers which are used in hostile industrial environments. The two fabricated detector constructions described are a basic two-channel thermoelectrically cooled detector and a self-contained four-channel detector assembly in which all the supporting functions needed by photoconductive lead-salt detectors are incorporated. The paper also deliberates upon the limitations of the multichannel detector technique and presents the performance level attained in the accomplished detectors.
This paper discusses the design of a Staring Radiometer to operate principally in the infrared waveband. The basic concepts are that it should incorporate a reflecting optical system of large area and high quality and use the latest digital techniques for both processing and control. Different customer specifications may be easily incorporated due to the modular design. An analysis of instruments made in the past few decades indicates that little redesign or updating has occurred, although PC computers have been added for data reduction purposes. This implies modernisation, making the old hardware look impressive. However, it is the hardware that limits the performance, so this was the area to which we addressed considerable design effort. In the 1960's the Barnes 4" radiometer was developed to quite a high level of sophistication. Discreet filter and circular variable filter wheels were incorporated for spectral analysis and the electronics progressed through the transistor stage into the microcircuit era. However, the optics design is poor, has gross aberrations and by modern standards poor temperature stability. Several other manufacturers have made radiometers but the designs have still not progressed significantly. Customer specification is now outstripping instrument capability.
This paper reports the use of Raman microscopy to investigate the deformation properties of fibres and of composites. In the past the authors and others have found that the Raman active bands of high modulus fibres can be sensitive to the level of strain in the fibre. Such fibres include polydiacetylene single crystalsl-3 , carbon fibres6, Kevlar5, poly(p-phenylene benzobisthiazole) (PBT) fibres6, poly(p-phenylene benzobisoxazole) (PBO) fibres' and silicon carbide fibres8. Two types of applications are discussed here. The first is to follow the deformation of individual bonds in a single fibre. The second is the use of this information to investigate the micromechanics of composites reinforced with such fibres. That the technique is applicable to composites is well established9 and so here we concentrate on some latter results.
A miniature infrared semiconductor laser based Doppler velocimeter system has been built and tested for use in characterising particle dynamics in fluid flow. Validation tests confirm that the instrument can perform just as well as established, visible wavelength, gas laser systems. The types, operation and approximate costs of the infrared lasers that could be used and the detectors operating in their wavelength range are briefly discussed. Future development and applications are also outlined.
The use of satellite-borne sensors for remote sensing in the visual waveband in now a well established technique. There are many application areas in which an extension into the thermal waveband has been shown to be beneficial. The technology for such infrared (IR) satellite systems is arguably less well developed than that for the visible sensors, for instance compared with the high spatial resolution and area coverage of modern commercial satellites such as the French SPOT series. Infrared technology has, however, progressed markedly in recent years for terrestrial requirements - the application of these advances to the remote sensing area is therefore studied. The constraints imposed by using terrestrial IR system technologies in space-based remote sensing systems are outlined and an indication given of the future requirements on IR sensor components for space applications.
The current European Meteosat satellite system is planned to be operated through 1995. By then, the basic concept will be some twenty-five years old. Work is now progressing to define the replacement, second generation system. This paper identifies the infrared requirements and the technical and technological concepts and problem areas of this new system.
The Improved Stratospheric and Mesospheric Sounder (ISAMS) is an eight channel infrared radiometer which uses the technique of pressure modulation radiometry to measure the temperature and composition of the upper atmosphere. ISAMS will be one of nine main experiments which will be launched on the NASA Upper Atmosphere Research Satellite (UARS) early in the next decade. The programme is directed at studying radiation, photochemistry, dynamics and their interaction in the Earth's atmosphere. ISAMS has an optical system which is designed to produce a well-defined and accurately pointed field of view and it must be critically aligned to yield the expected performance.
The use of thermal imagers within the Central Electricity Generating Board (CEGB) to monitor plant performance is described. Helicopter-borne high resolution thermal imagers are used to monitor the transmission system and the range of defects that can be detected has been extended in recent years. Similar equipment is used to monitor cooling water discharge behaviour over a tidal cycle while satellite imagery is employed to analyse general warming of the water near a power station. The applications of fault detection and plant monitoring to electrical plant and heated surfaces within substations and power stations is described for several plant items.
Laser beam profiling measurement is a difficult task to perform. Various techniques have evolved over the past twenty years. These have ranged from intercepting the beam with a simple piece of paper and viewing it by eye to x,y scanning of the beam with a simple detector. The drawbacks of these approaches range from inaccuracy to slow capture of data. A need exists for a fast real time detector that can operate in a staring array mode. It must use a wide spectral range to cover lasers operating out of the visual waveband, particularly the middle and far infrared. High definition staring arrays operating at these w.ivelengths are only at the research phase, except one. The pyroelectric vidicon has been commercially available since the 1970's. Not often thought of as a staring array it is however, a very good one. A 16mm slice of D.T.G.S. gives a circular array of approx. 200 by 200 pixels. Spectral response is flat from ipm to 20μm when combined with a ZnSe faceplate. Signal readout is by scanning with an electron beam. These devices are used in low cost thermal imagers operating in the 8-14μm window. We have optimised the tube and camera operation to perform laser beam profiling. These changes take into account the much higher power available from a laser and have concentrated on extending dynamic range. This has lead to a peak signal to peak noise ratio of 30:1. Care has been paid to the optical path to minimise unwanted moire fringes. Maximum power for signal overload and damage threshold have been verified together with ensuring a linear transfer function in the normal operating range. Both C.W. and pulsed lasers can be accommodated. A mechanical shutter allows capture of single pulses from lasers of less than 500Hz rep rate. The research allows TV images of laser profiles. However, other means is display and analysis have been investigated. Firstly a pseudo 3D display utilising an oscilloscope providing real time, low cost performance. Secondly computer analysis of the images allows high accuracy ,nd quantitative data to be extracted. These developments permit laser profiles to be carried out as a matter of routine and at moderate cost.