A great many advances have recently occurred in the fabrication of high density, two-dimensional IR detector arrays using CCD and CID technology, as well as novel packaging techniques. The present state-of-the-art in two-dimensional mosaic arrays is summarized and examples of imaging and non-imaging applications are given.
A systematic method is presented to design and evaluate mosaic sensors for detecting targets in the presence of background. The basic sensor system includes optical elements, a matrix array of discrete detectors, electrical filters, and signal processing electronics. Major considerations in synthesizing a mosaic sensor are described. The process starts by translating mission requirements into quantities such as sensor sensitivity and resolution. The initial sensor design (optics and focal plane) is then configured. Response to target and background sources as well as detector noise is examined. The resulting point design is then evaluated against mission requirements. The process is recycled until the mission requirements are satisfied.
Applications of charge coupled devices (CCDs) for reading out high density detector arrays are reviewed; the use of indium antimonide, mercury-cadmium telluride, and extrinsic silicon detector materials and associated focal plane assemblies is emphasized. The new flexibility available by employing high density detector/CCD structures is illustrated by design examples, including those of representative scanning and staring sensor concepts. The increased number of detector channels and the greater sensitivity of advanced infrared sensors places an ever increasing burden on the associated signal processing electronics. The low power and small size of CCD structures make them very attractive for a variety of analog and digital processing functions. Specific examples discussed include analog matched filters, recursive filters for operations on multiplexed data streams, line converters, and digital memories.
This paper discusses four types of (Hg,Cd)Te photodiodes developed recently at the Honeywell Radiation Center: 1. 2.06μm (Hg,Cd)Te avalanche photodiodes 2. 10.64m (Hg,Cd)Te photodiodes 3. High D* 10.6μm photodiodes with RoA products of 0.7 ohm-cm2 4. Thermoelectrically cooled 10.64m photomixers The 2.064m avalanche photodiodes were developed for the Q-switched Ho:YLF laser. The structures exhibited avalanche gains from 9 to 36. The 10.6μm photodiodes have average quantum efficiencies of 30 percent. This program has produced 5 element linear arrays with 250μm x 250μm elements, 17μm spacing and 350 MHz bandwidth. RoA products as high as 0.7 ohm-cm2 have also recently become possible in 10.64m (Hg,Cd)Te photodiodes. 10.6μm diodes operating at 170°K with a 6-stage thermoelectric cooler have high quantum efficiency (20%) and moderate D* and are suitable for direct detection or heterodyne applications requiring 100 MHz bandwidth.
The RM-20B mosaic differs from the types of systems that have been investigated in the past in that it only responds to image intensity modulation in its image motion-compensated (stationary) field of view. These intensity variations could be the result of either target motion or absolute radiance level shifts. If the background is relatively constant within the frequency band of interest, the number of false signals that are generated by the detector will be greatly reduced and the signal-to-noise ratio will be improved, resulting in a higher probability of target detection and lower data rates. If, however, the background has scintillation within the sensor bandpass, noise signals will be produced. No flights to date have made any measurements of background short-time (less than a second) variations. This paper discusses one attempt at obtaining mosaic data.
The RM-20A Radiometric Measurements package consisted of an optical system which included an internal dithering mirror, optical filters, a detector focal plane, data conditioning electronics packages, gimballing and servo control mechanisms, passive cooling and thermal control, and a logic unit for commanding. Radiometric measurements for both backgrounds and targets were planned to be performed by preprogramming the motion of the radiometer to retain the background of interest or the target within the field of view. The sensor consisted of an all reflective corner-corrector Schmidt optical system which focused incoming energy on a focal plane consisting of nearly 600 indium-antimonide photo-voltaic detectors and 20 silicon detectors for observation in the MWIR, SWIR, and visible spectral regions. It was to have been launched into a circular polar orbit onboard the P72-2 spacecraft in April 1975; however, the spacecraft did not achieve orbital flight because of a launch vehicle failure. Nevertheless, a brief description of the RM-20A experiment is expected to be of interest to the photo-optical instrumentation community.
Modern scanning radiometers may produce sufficient data to completely inundate the data user. This paper describes such a radiometer, the methods used to select and distill the data, and data presentation formats. The instrument, the RM-20A Radiometric Measurement package, was the latest in a series of Lock-heed Missile & Space Company designed and operated satellite-borne infrared radiation measurement payloads. It was designed to gather information on geosphere and space backgrounds observable in MWIR and SWIR bands. Data rates were on the order of a megabit which dictated efficient data handling techniques in order to accommodate both overall background surveys and detailed analysis for phenomenology purposes. The instrument will be described only in detail sufficient to make data processing problems and objectives understandable. Emphasis is on the processing required to present and format the data for users with varied requirements. Topics covered include removal of instrument effects from the data, transformation and calibration of data-so that it can be compared with that gathered by other instruments, gray scale picture composition, transfer function and PSD generation and tracking of fixed and moving points by data processing.
The thermopile has undergone tremendous changes since it was first used as an IR radiation detector over 150 years ago. Thin film construction has permitted the production of detectors that are physically small and extremely rugged, and with better response times and responsivities than their mechanical predecessors. In the past five years, manufacturing processes have been developed to make the thin film thermopile an economical candidate for many commercial applications, including non-contact temperature sensing, gas analyzers and fire and intrusion detection. The construction and performance of the thin film thermopile will be described as well as their use in several commercial applications.
Since the summer of 1959 a one-week intensive course on Fundamentals of Infrared Technology has been offered through the Engineering Summer Conferences, College of Engineering, University of Michigan. That first course was presented by five faculty members* from the Willow Run Laboratories, all of whom are still active in this and/or closely related fields. William Wolfe and I were co-chairman of that course for several years. The course is still given now under the chairmanship of A. J. LaRocca with lecturers largely from ERIM, formerly the Willow Run Laboratories of the University of Michigan. Prof. Wolfe is an active participant.
Infrared measurement programs are greatly affected by the medium through which radiances must traverse from a source to a sensor. With most civilian and military optical systems the optical path must include, wholly or in part, the earth's atmosphere. Failure to account for the actual state of the atmosphere along the path at the time of the measurement can severely limit the success of any mission. Conversely, the judicious application of meteorological resources to these programs, in the form of appropriate weather climatologies, observations or forecasts, can greatly enhance their chances for success. This paper describes the utility and availability of various meteorological data and gives examples of the application of meteorological support to certain military programs.
Geostationary orbit is a unique vantage point from which to view the earth and its cloud system. Since the weather moves under the satellite rather than the satellite over the weather as in lower orbits, any point within view can be observed continuously, if desired. The great distance from earth, however, imposes severe constraints on the design of the viewing sensor. Simple photometers taking advantage of the motion of spin-stabilized Applications Technology Satellites to generate one dimension of scan have demon-strated the great utility of geostationary observation for weather research and forecasting. Spin-scan sensors with vastly improved capability are now operational aboard Synchronous Meteorological Satellites; even more advanced sensors are now under development for next-generation spacecraft. This paper describes these sensors and discusses the operational requirements for which they were designed.
Fourier transform spectroscopy is a nineteenth century technique which is continuing to develop in the twentieth century. In this paper we discuss (1) Fourier transform spectrometer modulators for light sources, (2) high temporal resolution Fourier transform spectroscopy of multiple fast pulses, and (3) correlation which allows the drawing of maps in "probabilities" rather than in colors.
An optical method for measuring the carrier recombination time in semiconductors is described. In particular, this method allows for the measurement of lifetime with high spatial resolution. Results are presented which demonstrate the capabilities of the technique and illustrate its application to the detection and characterization of defects.
This paper presents a brief history of optical heterodyne detection of incoherent sources followed by a discussion of the current status of the field as well as possible future applications. Attributes of optical heterodyne detection such as high spectral resolution (λ/Δλ > 106), high sensitivity (≈10-19 W/Hz), and preservation of the signal phase will be discussed. Current applications of optical heterodyne detection of incoherent sources include stellar interferometry, solar radiometry, and the measurement of atmospheric absorption of laser radiation. Each of these experiments will be described, particularly the absorption measurements along the earth-space path for HF, DF, and CO2 lasers. Experimental data will be presented to verify the usefulness of these techniques as well as to compare their performance against theoretical predictions. Possible future applications of optical heterodyne detection of incoherent sources will be discussed including remote detection, monitoring, and tracking of atmospheric pollutants on a local or global scale.
This paper summarizes the optical design of a large aperture telescope for near IR imaging onto a linear array of detectors. System performance is described in relative terms because specific data relating absolute performance characteristics is classified.
Two integrating spheres have been developed to act as in interface between a monochromator and instru-ments under calibration. The spheres are designed to provide a diffuse, extended source and attenuate the signal sufficiently so as not to saturate sensitive instruments. One sphere is coated with a BaSO4 paint which provides a diffuse, highly reflecting surface in the 0.3 to 1.5μm spectral region. This sphere is operated at ambient temperatures. The second sphere is peened to create a diffuse surface and then is coated with copper to obtain a high reflectivity fran 1.5 to 8μm. The latter sphere is cooled to liquid nitrogen temperatures to eliminate self radiation in the spectral region of interest. Comparisons between observed spectral performance and theoretically predicted results are presented, and the gonianetric characteristics are described.
Viewing technology by infrared radiation, emitted and reflected, rivals that by low-light-level illumination, such as starlight. Parallel research and development in these fields have mainly been concentrated on instrumentation operating within the three atmos-pheric transmission "windows", the visible, mid and far infrared waveband regions of the electromagnetic spectrum. Both technologies have produced systems that have military and law enforcement applications but they are also being used for important peaceful applications; satellite surveillance for the Earth's resources, search and rescue; medical diagnoses, early warning machine breakdowns and the conservation of heat energy.
Pyroelectric detector technology has emerged from the status of laboratory curiosity to provide a wide variety of practical sensors and instruments. The characteristics of pyroelectrics are described and compared with those of other infrared detectors. Principles of operation and important design considerations and material properties are discussed. A number of instruments and their applications are described.
A radiometer using an electrically calibrated pyroelectric detector has been developed. The system, using a number of unique concepts, was designed to be a truly useful measurement tool for optical radiation of wavelengths from 0.4 to beyond 12 μm at power levels of microwatts. No standard sources are required for calibrations.
This paper is a discussion of the experimental techniques presently being used to characterize the Electrically Calibrated Pyroelectric Radiometer (ECPR) and of the degree of accuracy attained, to date, with these techniques. The results reported are an indication of the extent to which an ECPR can be regarded as an absolute radiometer for use as an optical calibration standard in place of a standard source.
Infrared thermography has become an accepted technique for nondestructive testing and thermal inspection problems . Such applications often require knowledge of the temperature distribution over a localized area and much of a thermal picture is extraneous, useful only to position the field of view or locate the desired regions of interest. A battery operated hand-held viewer is described which superim-poses a graph of the temperature distribution along an indicated line, onto a direct visual image of a two-dimensional field. This is accomplished by an oscillating dichroic mirror, one side of which produces an infrared, single-line scan with a pyroelectric detector, while the other side causes an orthogonal array of 18 red LED's to scan across the field of the observer. The oscillating mirror is transparent in the blue-yellow spectral region so that the viewer sees the red diode array superimposed onto a blue-yellow visible image of the field. Appropriate LED's in the array are switched on depending upon the amplitude of the infrared signal, to generate the thermal profile or graph. Temperature variations down to 0.2°C can be accurately measured with a spatial resolution of 4 mrad. The operator observes the scene through the view-finder of a reflex camera, and can make a film recording of the subject and thermal profile at any time. Applications to field, and in-plant, thermal inspection will be illustrated.
Pyroelectric imagers--now beginning their second decade of existence--are on the verge of becoming practical devices. As a result of recent improvements, they show real promise in providing long-wavelength infrared imaging systems featuring moderately good performance along with uncooled operation and relatively low cost. Various approaches to pyro-electric imaging are summarized; the pyroelectric vidicon is discussed in more detail, since it is the form of pyroelectric imager whose present progress indicates the greatest utility now and in the near future. Examples are presented of thermal imagery taken with a pyroelectric camera system developed at the Naval Weapons Center, which incorporates an image-difference processing technique. Areas of needed research and development are outlined, along with expected future performance levels and potential applications.
In recent years pyroelectric detectors have been recognized as very useful detectors for very short laser pulses. Detectors with response times of 500 picoseconds are now commercially available and rise times as short as 13 picoseconds have been reported. The spectral response of high speed pyroelectric detectors has been extended to yield a fairly uniform response from X-ray to submillimeter waves with no sacrifice in response speed. For moderate speed detectors with rise times below 70 MHz a variety of amplifiers can be used with the detectors to improve the sensitivity of the detectors. The present characteristics of high speed pyroelectric detectors are discussed in the following paper.
Over the past four years the technology involved in the construction of large, high power, short pulse CO2 laser/amplifier systems has advanced to the point where 10 kJ systems are currently in the construction phase and 100 kJ systems are being seriously considered for future development. The main emphasis of these machines has been toward laser-fusion studies. This application has led to many unique requirements on the laser systems themselves and to sophisticated interfacing problems and solutions between the laser devices and the fusion target devices. For these reasons, the problem of adequate IR diagnostic techniques and devices has been an important one and will continue to be so during the future development of the laser fusion program.
Pyroelectric detectors have been employed in several spaceborne instruments in recent years. Primarily they have been used in instruments designed to measure the temperature and humidity profile of the earth's atmosphere and to collect data in support of studies of the earth radiation budget. Pyroelectric detectors are being used in similar instruments now in the development and fabrication stages for future launches. Additionally, an infrared radiometer is being designed for the Pioneer-Venus mission scheduled for 1978 which will use pyroelectric detectors.
The pyroelectric vidicon and its performance characteristics are briefly reviewed, and attention is centered on the Philips' method for generating a pedestal current. This is done by pulsing the cathode during the horizontal flyback period to a potential such that the beam emitted during that time will strike the target with an energy above the first crossover for TGS. Features of the pyroelectric vidicon which must be taken into account for selecting a camera are: signal currents of about two orders of magnitude lower than those in a conventional vidicon, tube electrode voltages, and pedestal current. Field tests with a camera system having an MRT of 0.3°C at 100 TVL with f/1.0 germanium optics showed the usefulness of this relatively low-priced, uncooled, TV compatible, thermal imager. Potential improvements could result in an MRT of 0.3°C at 280 TVL.
A survey is made of the principles and methods involving scanning the field of view of a single infra-red detector to form a thermal image or "thermogram." Scanning parameters and practical tradeoffs are considered as well as scanning methods ranging from oscillating mirrors, rotating drums and prisms and counter-rotating prisms. Also considered are signal processing and display techniques and methods of image enhancement.
There is a myth which says it is a simple matter to "spin-off" military-supported technology into practical civilian hardware. Infrared system developers are particularly vulnerable to this misconception. To be sure, practical applications in the civilian market require vastly different systems which must either be optimized to meet dedicated and specific non-military requirements or are sufficiently flexible to be self-tailored to satisfy many diverse and imaginative uses. Moreover, practical applications require that infrared systems be not only detection devices, but also measuring devices; complete with simple-to-use controls and calibration capabilities. Unlike most military systems, the practical infrared system must have complementary data analysis devices, which can present the sought-after information in a variety of formats to be most beneficial to the user. Finally, all hardware must include extensive software in order to be reliable, and, especially, cost-effective and thus truly optimized for practical applications.
Fast scan infrared imaging devices present a flickerfree or continuous image to the eye. Theoretical performance limits are presented for these systems operating in the 3 to 5-μm and 8 to 11-μm spectral bands. Efficiency factors for available systems are given, which match the observed performance to the theoretically limited performance. The improvement in Minimum Detectable Temperature attainable with conventional frame integration techniques is shown.
Advances in technology have brought about IR thermal imaging systems with faster scan times and higher spatial resolution. This is in part due to the use of the mercury cadmium telluride (HgCdTe) detector which provides system performance advantages in evaluating temperatures up to 200°C. High spatial resolution permits the detection of thermal gradients in small electronic components and can reveal small voids and defects in materials. Thermal profiling of electronic circuit boards can be used for design evaluation and production testing. Effective use of this technique should take into consideration variations in emissivity of the material being studied. Examples of how to correct or compensate for these emissivity variations will be presented. Detection of voids and flaws in materials often requires the application of heat or cold to the material being investigated. This produces a surface thermal gradient which depicts the underlying abnormality. Approaches to the use of this technique in void detection will be presented.
The process of forming thermal images of microscopic targets had its practical beginning in 1964. Starting as an infrared microscope equipped with a motor-driven substage that provided X -Y scanning in the object plane, the instrument was developed to incorporate torquer-driven mirrors to accomplish scanning in the image plane. Advances in optical and electronic processing have produced significant improvements in image quality and in the variety of presentation formats.
This paper briefly describes the evolution of real time thermal imaging sensors, current design criteria and techniques, and concludes with an example of state of the art hardware and a look at the future., The relationship between optimum sensor implementation and available i. r. detector technology is shown with regard to scanning techniques and operating wavelength.
The HHTV is a lightweight, handheld medium resolution, medium sensitivity, battery powered, passive in-frared thermal imaging system developed for use by reconnaissance and combat elements of the Army. It provides passive thermal surveillance, detection, recognition and observation of personnel, vehicles and buildings in total darkness, in daylight and in rain. It will also penetrate light fog, smoke and targets partly obscured by foliage or camouflage. It is composed of a viewer, a battery pack, a charger-adapter, a connecting cable, a carrying bag and transit case. An oscillating mirror is used to produce optical scanning of the scene by a linear array of 48 PbSe detectors in parallel producing a rectangular field of view. The detectors are thermoelectrically cooled by means of a 4 stage peltier cooler that maintains the detectors at 195°K.
The PROBEYE Infrared Viewer* is a commercial IR imaging device operating in the 3.0 to 5.0 micron region. Since its introduction to the public, it has found application in the areas of fire fighting, police services, underground mining, electrical inspection and numerous other fields. The design and applications problems associated with bringing a sophisticated high technology device to a diverse commercial market are reviewed. A general approach is presented for solving these Iproblems, using the PROBEYE Infrared Viewer as a specific example.
This paper examines the key parameters effecting the performance of infrared. line scanners and presents examples of two equipments optimized for different operational requirements. The analysis includes a consideration of key target and atmospheric effects, and performance comparisons of common scanning and recording techniques. A sensitivity analysis relating NET, resolution and to system parameters and a discussion of the elements limiting the modulator transfer function are also included. Curves are developed to illustrate parametric relationships. Equipment examples include a brief description and sample imagery from the RS-18 and the RS-700 infrared line scanners.
The performance of passive sensors for surveillance, radiometry, spectroscopy, and astronomy is analyzed using idealizations of engineering features. Sensors are characterized by a finite number of degrees of freedom in each of two angles, wavelengths, and time. An optimum number of degrees of freedom is found to sense a target field in four dimensions. Degrees of freedom are quite freely inter-changeable between dimensions of different kinds. An optimum number of output states is related to the sensing or measurement requirement. An optimum weighting is found for averaging degrees of freedom into output states. Simple equations relate performance to an index of cost. Examples apply the results to estimate limits to sensor performance for several applications.