MTFs are usually computed indirectly from spread functions. The patterns used to generate these functions lead to certain problems in infrared systems. Square wave patterns have some advantages but also have some disadvantages. Sine wave patterns are useful but generally must be produced as area patterns. Various ways of using sinusoidal patterns are described.

Several state-of-the-art detection and image systems require synchronous high-speed shuttering of incoming irradiance. This shuttering action is necessary in many instances to increase signal-to-noise ratio, obtain high-speed (low-retention) imagery, and provide single-event observations. Presently, this type of "snap-shot" imagery is approximated by rotating chopper wheel methods that sweep an aperture across the focal plane. At faster aperture rates, these mechanical chopper systems become more complex and maintenance of image fidelity is very difficult. This novel, spectrally selective shutter mechanism provides true "snap-shot" imagery. Despite some limitations, such a mechanism is ideally suited to high flux, high background, and rapidly changing imaging visualization, and can be used to monitor flow visualization, chemiluminescence phenomena, and laser operation. The optomechanical techique described in this paper uses the rotation of one or two narrowband spectral filters to provide open-shutter times in the millisecond range. The resulting performance of the two-filter assembly is governed by the physical principle that increasing angular tilt of a narrowband interference filter causes the bandpass parameter to shift progressively toward shorter wavelengths. Data presented in this paper demonstrate that the spectral shutter technique can provide repetitive open-shutter times in the low-millisecond range, with true "snap-shot" images synchronized to video rates. Both advantages and limitations of this spectrally selective shutter are discussed and compared to typical mechanical chopper wheel methods. Specifically, performance advantages include the capability to provide (1) "snap-shot" imagery that always encompasses the entire field of view, (2) self-contained spectral selectivity for focused signal irradiance, (3) greater transmission efficiency during open-shutter times, and (4) adaptability to a wider variety of optical systems.

Indium Antimonide detectors have been fabricated with characteristics optimized for operation at liquid Helium temperatures. Responsivity and electrical characteristics of these detectors have been measured and are reported here. Results show that no significant loss of responsivity occurs in the three to five micron region, as had been previously reported. Also, a significant reduction in capacitance (factor of 4) has been realized.

Experiments were conducted to determine the influence of background clutter on target detection criteria. The experiment consisted of placing observers in front of displayed images on a TV monitor. Observer ability to detect military targets embedded in simulated natural and manmade background clutter was measured when there was unlimited viewing time. Results were described in terms of detection probability versus target resolution for various signal to clutter ratios (SCR). The experiments were preceded by a search for a meaningful clutter definition. The selected definition was a statistical measure computed by averaging the standard deviation of contiguous scene cells over the whole scene. The cell size was comparable to the target size. Observer test results confirmed the expectation that the resolution required for a given detection probability was a continuum function of the clutter level. At the lower SCRs the resolution required for a high probability of detection was near 6 lines pairs per target (LP/TGT), while at the higher SCRs it was found that a resolution of less than 0.25 LP/TGT would yield a high probability of detection. These results are expected to aid in target acquisition performance modeling and to lead to improved specifications for imaging automatic target screeners.

Infrared coatings are required on both surfaces of infrared windows to increase transmission and thus enhance system performance. For certain applications, one of the surface coatings is required to have deicing, defogging, and EMI (Electro-Magnetic Interference) attenuation capabilities. This paper deals with the transparent infrared coatings, including antireflection, conductive and induced transmission coatings for application in sensor systems. The wavelength ranges covered are 3.0 to 5.0 and 8.0 to 12.0 microns. Theoretical aspects of the design techniques are discussed in detail. The experimental spectral data is presented for various coatings on various substrates. In addition to the spectral data, data on the mechanical and environmental durability of the coatings is also presented. The mechanical and environmental durabilities of the coating are very important for military systems such as electro-optical sensor systems for use on aircraft, submarines, tanks, and ships. The transparent antireflection coatings are sometimes also required to have rain erosion resistance. Data on such coatings is also presented.

This paper presents a method to determine the resolution of an airborne Thermal Imaging System (TIS) under the conditions and in the environment of typical operation. By determining the resolution of the entire system (e.g. sensor, aircraft, display, pilot) a more realistic measure of the systems true resolution can be determined. The effects of Atmospheric Transmission and Target Radiation are also included in the evaluation.

Presented are calculations of Pd2Si and PtSi pixel spectral detectivitils as functions of background, operating temperature, and dwell times. Nearly BLIP (ΦB = 1012 cm-2 sec-1 )- limited performance can be attained when Pd2Si is cooled to T < 120 K and dwell times are longer than 0.5 sec; and when PtSi is operated at T < 80 K with dwell times longer than 0.01 sec.

Some of the major accomplishments of infrared technology in the decade 1975-84 are reviewed. The trend most influential on technology was development of sensors for use in space. Advances in technology to make these accomplishments possible include evolution of longer wavelength detectors, techniques to make large lightweight and adaptive optics, mosaic focal plane arrays using CCDs and evolution of staring sensors. Likely major challenges for the next decade are strategic defense from space, global resource management, and understanding of ecology and astronomy preparatory to space colonization. Technology changes to support these challenges are estimated.

An update of a paper presented ten years ago on single detector infrared scanners is presented herein. An overview is given of the most commonly used T.V. compatible systems, parallel and serial scanners and the comparisons thereof. Also described are a variety of image processing techniques for image enhancement and operator aides.

Nine years ago I gave a paper here summarizing the State-of-the-Art in two dimensional mosaic arrays. The standards were monolithic CCD and CID Silicon and InSb technologies; what is now called "Z" technology had just emerged. Since then the primary contenders have been planar hybrids and the "Z" configurations. In my opinion, costs of "Z" technology have come down to the point where these configurations will dominate. The future holds dramic growth in on-focal plane signal processing, ultilimately emulating, and perhaps surpassing, that of the eye and brain.

The Infrared Astronomical Satellite (IRAS) was successfully launched on 25 January 1983 and terminated science data acquisition on 22 November 1983. The in-orbit performance of the telescope has been described in two previous papers in these proceedings. A previous description of very preliminary scientific results from the mission has been given in these proceedings, while far more extensive reports have been given elsewhere. In this paper we will summarize some of the results obtained to date from the IRAS data. The work to date has sampled only a small fraction of the IRAS data; the study of the data from the IRAS survey will continue for many years to come.

A sophisticated deterministic interactive software model for computer generation of three-dimensionally projected infrared scenes has been developed. Scenes can be produced using either a self-emission or near infrared reflectance model. The software allows for generation of flight paths through a data base consisting of both feature and topography and near real-time display of stored precomputed images. The emphasis in the model development has been in computer generation of infrared scenes which accurately reproduce the characteristics of real-world imagery. The software combines computer graphics and infrared physics to produce synthetic scenes with the statistical properties of real scenes. Options exist for generation of images in near-infrared, 3-5 or 8-12 micron spectral bands including atmospheric attenuation effects. The three-dimensional projection algorithms allow for viewing of the scenes from any geometry and include concave and convex surfaces as well as hidden objects. Features exist for insertion of additional objects into the three-dimensional scenes. Thus targets, buildings, and other natural or man-made objects can be inserted with any orientation anywhere in the scenes. This allows full simulation of varying depression angles, range closure, and fly-over. The three-dimensional infrared background clutter model is an evaluation tool capable of both assessing system performance in clutter and increasing our understanding of clutter itself. The model in its current form represents a powerful tool for the fundamental understanding of infrared clutter. Possible applications include, but are most certainly not limited to, sensor operator training in the area of target discrimination with dynamic imagery, evaluation of automatic target recognizer (ATR) algorithms, and simulations allowing pilots to pre-fly missions.

A transmittance band model based on an equivalent absorption coefficient is presented. The form of the model and its band parameter determination scheme are presented. The model is shown to be useful for analyzing different empirical models, such as the double exponential function. Both models are developed for a single band of methane in the wavenumber region from 1150 to 1400 cm -1 at 5 cm -1 intervals.

SPRITE infrared detectors are now established as high performance components for use in thermal imaging systems operating both in the 3-5μm and 8-14μm bands. Such systems are currently under development or in production. This paper reviews the concept of the SPRITE, discusses the method of fabrication and describes their performance. Recent research work, aimed at understanding those factors controlling the spatial resolution, is described. The fundamental component to the Modulation Transfer Function (MTF) is the minority carrier diffusion, however measurements on a number of SPRITE arrays with a range of minority carrier lifetimes have indicated values in excess of this. This has been shown to be due to readout sampling and background radiation effects. As a result 8-14μm SPRITE element geometries have been designed and manufactured which overcome these. In addition for 3-5μm SPRITE, novel element geometries have been researched which have the effect of suppressing the minority carrier diffusion contribution to the MTF. This is particularly important in view of the inherently long lifetimes for 3-5μm SPRITE.

This paper outlines the basic parameters of the UK Class II Common Modules Thermal Imager and then describes the incorporation of modified optics and multiple SPRITE detectors to improve the basic system's spatial resolution and thermal sensitivity respectively.

Photovoltaic C.M.T.-Si hybrids have been demonstrated in a number of array configurations from 32 x 1 to 64 x 64. The photodiode and hybrid interconnection technology is based on the loophole technique, which has the main advantages of high density and therefore good material utilisation in two dimensional arrays. For linear arrays, the CCD multiplexer is suitable for most applications. For two-dimensional arrays,however,the co-ordinate addressed array may offer significant benefit over the CCq particularly at long wavelength. 32 x 32 arrays of both types have been fabricated. A co-ordinate addressed array of 11.4pm cut-off produced an NETD of < 0.1K in an imaging demonstration.

Infra-Red staring arrays using technologies suitable for low cost missile guidance systems have now been with us for almost a decade. The initial enthusiasm for these devices, which offered a substantial performance advantage over conventional scanned line arrays, was soon replaced by a more critical view of their applicability. A number of technical problems needed to be solved if these devices were to be used in some of the more demanding missile applications - problems in the charge handling capacity and read out mode on the focal plane and in the cost and complexity of the supporting drive electronics and signal conditioning. This period of concern has now been replaced by a renewed optimism as a new generation of focal plane architectures is becoming available and practical designs for the associated electronics are proven. As a result the system designer can now confidently propose systems which incorporate detectors with complex focal plane structures. In this paper we review the requirements of sensors for a variety of military applications and show how the new focal plane architectures can be used in these roles. Prototype hardware has been built to demonstrate the feasibility of such staring sensor systems.

Large arrays of pyroelectric detectors; linear or two-dimensional, have the potential to satisfy many of the increasing requirements for IR detection and imaging using uncooled sensors. This paper examines the design of these arrays and the technologies required in their fabrication. Key design features are the interfacing of the pyroelectric elements with low noise silicon preamplifiers or multiplexers, the thermal isolation of the pyroelectric elements, and device structures which lead to a reduced susceptibility to microphony. The basis for these designs is the well established lead zirconate ceramic as the pyroelectric. The technologies include the reticulation of this material by ion beam milling, and the bonding techniques for mounting the detector elements such as solder bump bonding.

A new mode of operation of photoconductive detectors is described in which a non-linear current-voltage characteristic is induced by illumination. Outputs at harmonic frequencies can be obtained from devices biased with alternating current or at the modulation frequency of a modulated, alternating bias. Several different ways of achieving the non-linearity are described, one of which uses conventional detector structures. The advantages of this mode of operation are that the large bias-voltage pedestal, normally associated with long-wavelength photoconductive detectors, can be separated from the photo-signal by simple electrical filters and that the problem of flicker noise, in both the detector and the following electronics, is considerably reduced. Photoconductive devices thus become competitive with photodiodes, which may be more difficult to produce with ideal performance and stable characteristics, in detecting radiation with very low modulation frequencies. Possible applications for the device may be in slow, parallel-scanned linear arrays; in "staring" arrays; in ultra-sensitive detectors employ-ing long integration times, or in position-sensitive, point source detectors.

This paper reviews and updates the progress in pyroelectric vidicon research and development. The principal items are high readout efficiency for low picture lag, high thermal impedance at the picture element for a high spatial resolution, good target uniformity and cosmetics, low readout noise, and camera design and signal processing. To illustrate the camera potential, a portable camera designed as a fire fighting aid is described.

A discussion is presented of a proposed modification to the molecular absorption band models in the LOWTRAN code for the uniformly mixed (N2O) CH4, CO, 02, and CO2) and the trace (NO, NO2, NH3 and SO2) gases. The transmission function adopted for each model of a double exponential defined by three absorber parameters and a single spectral parameter. All the parameters were determined optimally through a numerical procedure that incorporates line-by-line and measured transmittance spectra. Vertical concentration profiles are provided for these gases which may be used together with the 33-levels standard atmospheres in the calculation of slant-path transmittances. The present single model for the uniformly mixed gases in LOWTRAN is compared with the combination of the proposed individual models.

Infrared background data are usually presented in the form of time histories and various statistics. The statistics in the time domain include means, variances, autocorrelations, and histograms of various types. The statistic usually presented in the frequency domain is power spectral density (PSD). The data in either time or frequency domain may be useful depending on how the system designer chooses to implement his filtering system and perform his system calculation. This paper examines the requirement for consistency in the two domains and shows how well certain windowing techniques assure consistency between time and frequency domains. A particular technique is shown to give virtually perfect consistency. Data from the Balloon Altitude Mosaic Measurement (BAMM) are used to illustrate the results.

A positive miniscus germanium lens with convex elliptical surface is designed and fabricated for infrared horizon sensor applications. The performance of the lens is compared with a lens having spherical surfaces and designed for minimum spherical aberration. The design details and test results are presented in this paper.

A measurement and analysis effort to demonstrate the applicability of infrared spectroscopy for monitoring the performance of industrial flares is described. These flares are used commercially for the disposal of waste gases by combustion. Infrared spectral emissions from a standard, commercial flare were collected as a function of operating condition. Carbon dioxide and carbon monoxide concentrations were determined by iteration of emission spectra measured in the 1800 to 2500 wavenumber region against computed model spectra. Included in this paper is a discussion of the analysis methodology and field test results.

Absolute radiometric analysis of Landsat Thematic Mapper (TM) thermal infrared image data requires processing to remove atmospheric effects and knowledge of target material type in order to obtain kinetic surface temperatures. Results are presented in which a modified version of the LOWTRAN-5A atmospheric propagation model is used to remove atmospheric effects. Target emissivities are estimated by using shorter wavelength bands of the TM sensor to outline general land cover classes, and assigning an emissivity to the land cover type. By combining atmospheric effects, emissivity, and internal radiometric calibration data, surface temperature images have been generated. These images include corrections for internal sensor calibration, emissivity, upwelled radiance, and atmospheric transmission. These techniques have been implemented using parallel processing methods on an image display system resulting in relatively high image throughput rates. Using the higher resolution short wavelength data in processing the thermal infrared data has an additional advantage in that it gives the appearance of improving the resolution of the thermal infrared data. These displays clearly aid the assessment of thermal signatures.

With the ever increasing demand of superstructures by the space and defense industries, detection of flaws, voids, and unbonded regions has acquired tremendous attention. New thermographic techniques make it now possible to quantize the extent of internal dam-age and to locate the specific layer in which the flaw exists in both honeycomb and composite structures. The usefulness of this technique was demonstrated when several aircraft wing assemblies catastrophically failed during recovery. A non-destructive (ND) test program was initiated to assess the quality of brand-new wings. The IR test revealed large unbonded areas between the wing spar and face skin in some of the wings. Results from cross section examination of these wings were in complete agreement with those of the IR scan. Emissivity correction techniques were sometimes mandatory to enhance the ability of the thermographic equipment to extract information regarding the flaws. With video recording fast documentation can be achieved, and if the system is coupled to a video processor (minicomputer), further non-real time analysis is possible (Fourier transform, image averaging, contrast stretching, image enhancement, etc.) of the area in question.

Thermal (2.0 μ - 5.6 μm) measurements of the normal emittance (EN) of several diathermanous materials were made at 15.2°C, 4.9°C and -5.6°C. Calculations of the total hemis-pherical emittance (EH) were made from EN and plotted against the optical depth (YΔλx). A comparison of these data with a model proposed by Gardon indicates that at near-ambient temperatures they agree very closely. It has been observed that EN > EH by ≈ 5% for both weakly and strongly absorbing materials. This is attributable to phase differences in the multiply reflected internal radiation attempting to exit the specimen throughout π steradians. Other radiation properties of the materials, i.e. diffuse transmittance (TD), absorption coefficient yΔx, and absorption index k were calculated.

In a prior work analytical estimates of the saturation currents of ideal three-dimensional diodes were obtained. It was illustrated that the analytical forms obtained could also be used to provide an estimate of the photocurrents produced by these diodes when they are flood illuminated. This paper discusses the accuracy of the estimates obtained, the estimates from the point-of-view of experimental verification and extends the analysis to consider the influence of nonideal surfaces/contacts and optical masking. The results indicate that bulk generation saturation currents in photodiodes in three-dimensional structures can greatly exceed the saturation currents of planar diodes with the same junction area, but are less than indicated by thermal generation within a diffusion length of the junction. Nonideal surfaces/contacts tend to increase an already large saturation current influence, but not to the extent of their influence on planar diode behavior.