(i) The high speed of Fourier Transform spectrometry can give Quantitative spectra at a sufficiently high rate to be useful for on-line analysis in the wavelength 2.5-15 μm. By designing an instrument for on-line use, a simplified interferometric spectrometer has been developed at a cost that is viable for on-line use. The method may be applied for analysis of gases, liquids and certain types of solids. (ii) A single-component infrared analyser has been developed, which achieves absorption of the beam by the liquid sample using an attenuated total reflection crystal. Although the optics and wavelength selection method (interference filters) are conventional, the infrared measuring head has been built as a miniature sealed arrangement that can be submerged in the process stream if required. It has been found suitable for measurements on a range of samples including aqueous solutions.
This paper presents a summary of various applications of pyroelectric vidicons to thermal imaging of operating units in the processing industries. It is not within the scope of the report to provide detailed descriptions of the chemical engineering aspects of the work and the report is confined to a presentation of the range of applications covered and the rationale adopted in the survey work. Applications included heater ducting, boiler plant, rotating kilns, internally insulated reactors, fin fan coolers and insulated road tankers. Almost invariably the work was carried out on running plant. Thermal imaging was used to obtain only qualitative display of variations in surface temperature conditions. Where appropriate actual temperature measurements were obtained by emissivity compensated contact pyrometers.
Infra-red imaging techniques offer the possibility of mass monitoring the external temperatures of buildings such as factories and dwellings on a non-intrusive basis with the object of determining those losing an excessive amount of heat. It is shown that typically external surface temperatures are only a few degrees above ambient, and in order to relate thermal images to the surface temperature the emissivity of the material must be accurately known. Emissivities of common building materials in the range 2 - 5.6 μ have been determined and are tabulated.
In attempting to reduce the heat losses from buildings and other structures greater attention should be paid to radiation losses. These are less well understood and less easily controlled than conduction and convection losses. The sources of radiation range from the sun (6000K) to room temperature objects (293K) and the range of wavelengths being radiated is very large. Materials which are transparent at some wavelengths can be opaque or highly reflecting at others. Use can be made of such wavelength selective properties and new selectively reflecting materials are being developed. The requirement for windows for example are very different than for walls or for industrial insulation. Assessment of the properties of these materials requires new techniques both in the laboratory and in the field.
Moisture measurement by infrared absorption is gaining acceptance in many industries as a rapid, contactless technique which can cover a wide range of moisture values. Following laboratory investigations, Sira Institute has conducted several applications exercises demonstrating the on-line performance of the technique on a number of materials. For granular materials it is common practice to use a backscatter technique. The instrument can be mounted to view material as it passes on a conveyor belt and data obtained during on-line calibration trials on clay dust, sand, iron ore and coke, etc will be presented, together with installation details. In some plant applications the material can be viewed as it passes a window. The wetting up of peat in a mixer, and the drying of straw, are two such applications which will be described. In the above cases, information on the control systems employed and the financial savings resulting will be given. Certain materials such as iron ore, coal, are opaque to infrared radiation and investigations have shown that the infrared reflectance technique then responds to the thickness of the water film around the particles. For certain processes, such as pelletising and pressing, it is believed that water film thickness is the parameter which determines optimum process conditions.
Pyroelectric detectors are thermal sensors which monitor change in radiation power and are therefore well suited to surveillance applications. They operate without cooling and are readily used in alarm systems which are self contained, have low power consumption and are sensitive while maintaining an excellent false alarm rate.
A trap camera is an "on demand" surveillance camera, that is left unattended on a premises to photographically record intruders. A survey was made of the requirements of Police groups within the U.K. for such a device and showed that the only acceptable method of imaging, on economic grounds, was to use infr-red electronic flash incorporated in a new design of silent 35mm motor drive camera. An extensive market search indicated that no such camera was in production at the time of the survey. Infra-red light of the wavelength and intensity required to correctly expose Kodak High Speed Infra-Red film can be observed, even at high ambient light levels as a dull red. At near total darkness with the dark adapted eye, the infra-red flash becomes clearly visible. This was not acceptable for a multishot camera. The way in which this problem was overcome is discussed in the paper. Prototype models have been constructed under contract and these are now undergoing field trials. Quantity production by the same company is imminent.
Thermal imaging systems are, in general, considerably more effective than image intensifiers for surveillance at night, particularly for the detection of personnel, vehicles, boats, etc. Large thermal equipments exist for use on military vehicles and are capable of giving very high performance, usually at high cost and weight. The police have a requirement for a hand-held thermal imager with modest optical performance, but with a compact and lightweight design. This equipment is needed for direct viewing, usually at night, for the detection of missing persons, fugitives etc. in ground and air searches of countryside. A number of existing thermal imaging equipments, including pyroelectric vidicons, and scanned arrays with pyroelectric or cooled detectors have been evaluated. It is concluded that there is no equipment either available now or in the near future that meets the police requirement. A contract has therefore been placed for the development of a thermal viewer and the first of these is expected by September 1977; the specification for this equipment is given.
Infrared astronomy is considerably affected by the continuing advances in detectors, electronics and computing for control and instrumentation; it also makes important contributions in these areas. Ground-based astronomy at one to thirty-five microns is now background shot-noise limited for broadband photometry in most atmospheric windows. Present techniques under development emphasize higher spatial and spectral resolution, and on-line presentation of results. Telescope design has evolved to ensure lower instrumental contribution to the background radiation, and both imaging and positional control have improved to allow efficient utilization of the new instrumentation. In a non-specialist qualitative approach, some of the more interesting developments are briefly discussed.
The broad spectral response of pyroelectric vidicons has led to their se with a wide variety of lasers; moreover, the storage property of the pyroelectric target permits imagery with pulsed radiation. Specific applications include : 1. Recording interferograms for evaluation of infra-red optical materials and complete lenses. 2. Measuring the spectra of backscattered radiation from plasmas produced by pulsed lasers. 3. Mutual alignment of visible and infra-red lasers for precise intercomparison of wavelengths.
Infrared Astronomy is the last part of the electromagnetic spectrum to be developed. Over much of this spectral range, stretching from the visible to ~ 300 microns, absorption by water vapour and other gases in the atmosphere precludes observations from the ground except in those spectral regions where the absorption is low and so called 'windows' exist, such as at 10 and 20 microns. No good windows exist at longer wave-lengths where astronomical bodies at temperatures of a few tens of degrees radiate most of their energy. So, for much of the infrared region it is important to be able to get above the atmosphere. This can be done in a number of ways. To date observations have been made from aeroplanes, ballons and rockets and plans are well advanced for an infrared survey satellite and the use of the space shuttle. Each type of vehicle has its own particular advantages and disadvantages. Thus the use of an aeroplane, for example NASA's C141 (the Kuiper Airborne Observatory) in which a 1 metre telescope has been mounted, is very convenient and is ideally suited to making broad band observations. However, it is at a disadvantage for high resolution observations due to the lines from the remnant water vapour in the atmosphere and here observations from a ballon borne telescope are preferable but somewhat more difficult to make. Rockets are good in as much as they get above essentially all the atmosphere but the observation time is short. The main driver for an infrared satellite, which is a joint Dutch/US/UK enterprise, is to make an all sky IR survey at wavelengths between 8 and 120 microns. There is no doubt that a comprehensive survey out to such long wavelengths is urgently needed. Another urgent requirement is to achieve high angular resolu-tion at the longer wavelengths and this is the purpose of mounting a 3m. dish onto the shuttle. The equivalent NASA proposal is for a somewhat smaller telescope cooled to cryogenic temperatures to reduce the photon noise and so achieve a higher detector sensitivity.
The human body is an efficient radiator. Infra red energy can be detected and displayed to provide a thermal map of the skin surface. Many biological factors control skin temperature, and strict control of technique is essential, to establish meaningful measurements. A variety of options in instrumentation are currently available including computerised data processing. Temperature abnormalities may be used to aid diagnosis, and monitor treatment. Thermography can be used to indicate changes in thermal pattern, temperature range, and response to a stimulation test. In articular joint diseases, metabolic disorders, and circulatory diseases the value of quantitative thermography has been demonstrated.
Recent uses of infrared colour thermography in environmental physiology are outlined. These include analysis of the normal thermogram and recording, on colour cine film, the temperature changes that occur during exercise. Skin temperatures in warm ambient conditions and during exposure to direct sunlight have also been recorded and the cooling effect of a hot drink in warm weather has been demonstrated. The use of thermography to assess the effectiveness of garments for use in the harsh conditions beneath hovering helicopters is described.