Infrared astronomy can realize orders of magnitude improvement in sensitivity when the observing telescope is raised above the lower atmosphere. The Shuttle Infrared Telescope Facility (SIRTF) will combine this high sensitivity with the flexibility offered by the Space Transportation System: flights of 7 to 30 days repeated at 4 to 6 month intervals, the freedom to modify or replace focal plane instruments between flights, and electrical, cryogen, and data management support. A recently completed study has generated a preliminary design which demonstrates the feasibility of SIRTF. The 1. 0 to 1. 5 meter aperture, f/8 Gregorian telescope will be cooled to 20°K by a stored supercritical helium system. The telescope will be pointed and stabilized at two levels: the European-developed Instrument Pointing System provides primary pointing and stabilization; and an internal star tracker senses residual errors and drives a folding mirror inside the telescope to null the errors. The folding mirror can also be driven by square or triangular waves to provide space chopping or small-area scanning. Power requirements and data rates are compatible with Shuttle capabilities. SIRTF and its support equipment comprise one-half to a full Shuttle payload depending on mission duration.

The Infrared Astronomical Satellite (IRAS) will be used to survey the 8 to 120 μm spectrum of the entire sky to the faintest flux levels possible by using state-of-the-art detectors and preamplifiers. As a result of a recently completed study of the telescope and focal plane, a concept has been devised that demonstrates the feasibility of using stored cryogen to cool the telescope for one year of operation in a polar twilight orbit at an altitude of 900 km. Predictions regarding noise equivalent flux density, cryogenic life-time, and the number of noise spikes caused by Van Allen belt radiation are presented. The telescope is cooled both by supercritical and by superfluid helium. The on-board signal processing includes provisions for suppressing noise spikes.

The output of a scanning airborne LWIR radiometer observing stellar sources is treated as imagery . Techniques of digital image processing including frequency and spatial domain filtering are used to enhance the imagery, achieving signal-to-noise ratio improvements up to a factor of 6.24. Raw and processed imagery at 4 and 10 micrometers illustrate the techniques . The use of astronomical sources in conjunction with an internal pulsed photon source for sensor calibration is discussed.

We have studied a selection of infrared variable stars at wavelength 2.7 μm during 1971-1975 with data from U.S. Air Force satellites. Stars observed in this program are classified as long-period variable stars, semiregular variables, and irregular variables and are among the strongest stellar sources at this wavelength. In addition, a few new, as yet unclassified variable stars were identified during the course of the investigation. Time scales of reproducible variations range from a few weeks to a few years, and amplitudes of variation are as large as a factor of three for stars with periods of order one year. The minimum infrared flux density of a long-period star repeats accurately from one cycle to the next, whereas the maximum flux density was found to be unstable. This behavior may be related to the propagation of shocks in the stellar atmosphere near the time of maximum light or to coupling between large-scale convection and pulsation. It suggests that phenomena in these stars be timed with respect to minimum phase, rather than maximum phase as done previously. Maximum infrared flux density occurs after maximum visible light, whereas the visible and infrared minima are essentially simultaneous. The correlation of 2.7 μm and radio emission line data from one, well-studied long-period variable is consistent with the hypothesis that the H2O and OH circumstellar masers are saturated, if pumped by the stellar infrared flux near 2.7 μm, as suggested by Litvak. However, an alternate model, namely that the radio maser clouds are pumped by long-wave infrared radiation, cannot be excluded.

A number of infrared radiometers have been developed at the Santa Barbara Research Center for the determination of planetary thermal balance and surface thermal properties. These instruments have performed well on Mariners 6 and 7 (Mars fly-by), Mariner 9 (Mars Orbiter), Mariner 10 (Venus fly-by and Mercury Orbiter), Pioneers 10 and 11 (Jupiter fly-by), and most recently Viking Orbiter. All use thin-film antimony-bismuth thermopiles developed at SBRC. Details of design, construction, performance, and sig-nificance of the data are discussed.

An infrared system for measuring the spatial, temporal and low resolution spectral distributions of radiating sources is described. The system has three main subassemblies: a Data Acquisition subsystem consisting of a selectively filtered spatially scanning IR camera; a Display and Preprocessing subsystem; and a Digital Video Process subsystem. Unique features of the system include data display components which provide grey scale, two configurations of pseudo-color, and 3-D graphical displays, a video digitizing interface, and an interim storage facility. The system can be operated in a real-time or delayed playback mode. The IR Scanner camera (AGA System 680 Thermovision) provides 16 frames per second of an optional 10 X 10 or 2 X 2 fields-of-view, with 1.3 or .3 millirad instantaneous fields-of-view, respectively. Spectral content is obtained by changing discrete bandpass filters. System characteristics, atmospheric attenuation corrections and calibration procedures for direct source radiance determination from pseudo-color displays are given.

The detection of molecular line radiation is of interest in a variety of applications such as atmospheric pollution monitoring, investigation of astronomical sources, and basic spectroscopic studies. In the following discussion, the heterodyne detection of molecular line radiation is shown to have significant advantages over direct detection at longer infrared wavelengths. The development of a heterodyne receiver operating in the long wavelength infrared region using tunable semiconductor laser local oscillators is described. The techniques used to operate the receiver at selectable descrete wavelengths are applicable to the entire spectral range covered by semiconductor lasers. Results are presented for the heterodyne receiver operating in the 24-μm spectral region.

A brief overview of point and remote monitors that operate in the infrared region is given . At present, optical correlations techniques are widely used in point samples. Thus, a brief description of the historical development is given, which started with the nondispersive infrared (NDIR) technique and has recently emerged as the gas filter correlation (GFC) technique. The basic theoretical formulation for GFC is given. Infrared remote monitors are applied more frequently in recent times. They include both active and passive systems. These systems come in many configurati ons, providing line integral, line average and line profile data. The theoretical sensitivity of practical systems is discussed, including eye safety considerations for laser systems.

This paper discusses the problem of the remote measurement of tropospheric air pollution from aircraft platforms. Following a discussion of the energy sources available for passive remote sensing and the location of the absorption bands of the gases, it describes the spectral resolution that would be required and the relative merits of the shorter and longer infrared wavelengths. It then traces the evolution of one instrument concept (the gas filter correlation radiometer) to its present state, and describes flight results that show the technique to be capable of measuring carbon monoxide over water. A new instrument is described that will allow the measurements to be extended to areas over land.

A measurement and analysis program to determine the concentration of SO2 in a coal-burning power plant stack was conducted by a passive remote sensing technique, utilizing a PFS-201 Fourier Transform Spectrometer. SO2 concentrations were determined by measuring the radiance of the (w1 + w2) combination band at 2499.0 cm-1 (4.0 μm), while the exhaust gas temperatures were determined by measurement of the peak CO2 radiance at 2396.4 cm-1. Results of the remote measurements compared favorably with the in-stack Du-Pont Analyzer data.

Field measurements were carried out to determine the feasibility of using infrared television systems to measure plume characteristics of power plant stack emissions. Emphasis was placed on determining the suitability of these imaging systems for monitoring sulfur dioxide concentrations and effluent velocities in stack emissions. Specific objectives were: (1) to obtain experimental infrared data on stack plume characteristics, (2) to establish optimum infrared television system parameters for detection and measurement of these stack plume emissions, and (3) to determine the feasibility of using the General Electric infrared vidicon to monitor stack plume parameters of interest. This paper describes in detail the test equipment, measurement techniques, and resulting data associated with experiments conducted at the Duke Power Company Riverbend Station. Data on observed infrared emissions from refinery burn-off stacks are also presented for comparison.

The multigas analyzer simultaneously measures the concentrations of CO, CH4 and CO2 in flowing samples of automobile exhaust. Three channels share a single rotating gas correlation cell and measure the individual concentrations of CO and CH4. Two CO channels with different sample cell lengths extend the useful range. A rotating dual-filter system measures the CO2 concentrations. As many as three separate CO2 channels can share a rotating filter assembly. A system employing two fixed filters and two detectors measures the concentration of H2O and automatically accounts for a slight interference by this gas in the CH4 channel. Discrimination against other typical exhaust gases is excellent. An automatic gain control minimizes calibration drift. The ranges of measurable concentrations are 0.3 ppm (parts-per-million) to 3000 ppm of CH4; 0.7 ppm to 10% of CO; and 60 ppm to 30% of CO2, where the minimum concentrations correspond to the peak-to-peak noise levels with one-second time constants. The theory of operation, the measurement capabilities, and the physical characteristics are described.

Remote analytical sensing requires a high pulse energy tunable infrared source for detection of molecular species. This paper describes progress made in a Nd:YAG pumped, computer controlled LiNbO3 parametric oscillator with a tuning range of 1.4 - 4.4 μm The device is now well engineered and is finding applications in laser chemistry and remote air pollution monitoring.

Single-ended laser radars using discretely tunable infrared gas lasers have been demonstrated to be capable of high-sensitivity remote measurement of gases. Two systems have been investigated: (1) A deuterium fluoride laser was used for remote measurement of the integrated concentration of HCI, CH4, and N20 between the lidar system and a topographic target; and (2) a CO2 laser was used for range-resolved measurement of water vapor using radiation backscattered from naturally occurring aerosols in the atmosphere. Calculations indicate that range-resolved concentration profiles can be obtained for many gases at a range of 10 km using commercially available components.

The applicability of a high resolution infrared heterodyne radiometer for atmospheric temperature profiling is considered. Upwelling radiation at the 754.321 cm -1 (10° er 0-0110) and the 945.976 cm-1 (00°1-1000) rotational-vibrational lines of CO2 are monitored by a six IF channel infrared heterodyne radiometer with spectral specificity between 0.002 and 0.012 cm-1. Computer simulated retrievals have been carried out which indicate a maximum temperature inaccuracy of 3.5 K for vertical profiles between ground level and 50 km and a system integration time of 8 seconds.

An aerodynamically heated window can interfere in several ways with FLIR imagery. Uneven window heating causes uneven focal plane irradiation, a contrast gradient across the field, and blur because of point-to-point changes in refractive index. Window heating also increases photon noise, and in some cases reduces signal-to-noise because of reduction in transmission. This paper presents a method for computing aerodynamic heating of a window, starting with point-to-point total pressure patterns and evaluating each parameter in terms of its electrical analog. Window heating time constants are also computed in analogous electrical terms. Temperature patterns are converted into focal plane contrast gradients, image blur and MTF degradation. Examples are given of comparative performance of ZnS, ZSS and GaAs windows in a mach .8 sea level environment.

This paper presents an overview of multielement infrared detector array technology at the Santa Barbara Research Center. The paper discusses lead salt, indium antimonide, lead tin telluride, mercury cadmium telluride, and extrinsic germanium and silicon detector arrays. Examples of state-of-the-art arrays are presented for each of these detector materials. Two different hybrid detector/CCD array structures are described, an InSb/CCD sandwich structure using indium bump interconnects and a HgCdTe/CCD sandwich structure using evaporated interconnects. These techniques offer the advantages of low power, high density, low cost TDI on the focal plane.

Four noise sources occurring in an earth-viewing staring mosaic sensor mounted in a satellite are discussed. The four noise sources are (1) the internal system noise (detector and CCD), (2) the photon noise due to the background radiance level, (3) the noise due to background spatial characteristics scanned by an instability of the satellite, and (4) the noise due to the background temporal variations caused by cloud movement, solar movement, and scintillation. These four noise sources are affected by the particular sensor and their effect at the output of a sensor normally requires extensive calculations. A method of estimating bounds for each noise is demonstrated. This is done by approximating the actual functions by means of log-amplitude (Bode) plots.

Heretofore, production military missile trackers relied on opto-electroic systems which tracked the target as a point source. With the advent of charge-coupled technology sensor arrays and fast micro-processors, military missile trackers will be able to track imaged targets. Imaged targets contain a multifold increase in information content. To utilize this information content in real time during a tracking scenario, fast microprocessors solve tracking, countermeasures, predictive tracking, image correlation, windowing, and adaptive thresholding. The objective is to develop cheap strap-down missile trackers devoid of gimbals, gyros, and sundry hardware. This paper describes research to date on this objective.

A novel scanning sensor concept has been designed and evaluated for missile surveillance from an orbiting satellite. This concept, called a ring-field sensor, is capable of providing fast frame rates, excellent spatial resolution, and high radiometric sensitivity with relatively small optics. The scan implementation utilizes a continuously nutating, optically flat mirror in object space which exhibits very low momentum exchange with the spacecraft. Ring-field scanning combines most of the advantages of a spinning line array and a linear scanning line array for broad band systems without their major disadvantages. Furthermore, it is uniquely suited to predetection filtering over a wide field of view for background suppression. Incorporation of a Fabry-Perot etalon in the optics, for example, will result in improvement in signal to background noise but, more importantly, will provide suppression of the structured background by a factor of two or more. This performance improvement does not require a large number of detectors. The ring-field sensor concept is described, and the results of signal to noise enhancement estimates using the Fabry-Perot etalon are presented. Target and background spectra are included to indicate the basis for the estimates of sensor performance.

A simulation approach for the performance evaluation of both scanning and mosaic infrared sensor systems and their associated signal processing is presented. This approach allows a parametric exploration of design alternatives and environmental extremes. Various focal plane geometries and alternative signal processing algorithms can be investigated. The simulation has been implemented for maximum efficiency to allow the evaluation of system probability of detection and false alarm. rates. Microscopic effects, such as optical crosstalk, image motion during the dwell, assymetric point spread functions, and platform effects, are modelled. Important models within the simulation are: optics and detector, Time Delay and Integrate (TDI) and Charge Coupled Device (CCD) effects, object motion, and a band pass filter. The output of the simulation can be input to alternative data processing algorithms. Individual algorithms and configurations can be evaluated at several stages in the flow. The simulation has been configured to model both staring mosaics and scanning bar sensors. Data supporting model verification and an example of the application of the simulation to a scanning infrared astronomical satellite are discussed.

A high resolution fiber optics communications system (FOCS) for analog signals has been designed, built, and tested at the Frank J. Seiler Research Laboratory, USAF Academy, Colorado. The FOCS consists of a small transmitter and receiver pair and an optical waveguide. A combination of voltage-to-frequency-to-voltage (V/F/V) and pulse width modulation (PWM) is used to reconstruct a ± 10 volt analog output signal from an identical ± 10 volt analog input signal. A digital output is easily obtained since the data transmission is pulsed. The FOCS is equally applicable to free-space infrared communications. The advantages of fiber optics have not previously been available for general purpose data acquisition because their application has been limited to dedicated digital systems and to low resolution, high frequency video systems. Data collected on a very general V/F/V system is presented to give the designer information on V/F/V system dynamics at frequencies much higher than those considered to be in the V/F/V system's useful range for data acquisition and communication purposes. This data shows that the V/F/V process may be useful for servo loop applications at much higher frequencies than it is for data acquisition and communication applications.

Charge Coupled Device (CCD) imaging and processing arrays have shown promise in applications requiring integrated focal plane data processing such as found in certain "smart" sensor and data rate compression designs. This paper presents the results of a computer simulation effort to determine CCD imaging properties in both scanning and area array configurations. The ability to simulate imagery for a variety of array parameters is useful in the design of such imager/processor systems. Results of the study illustrate effects which are both general characteristics of sampled systems and peculiarities of CCDs. Included are resolution loss using computer generated targets, spurious signals due to the relative position of target and sample points, distortions due to linear and sinusoidal smear, effects of target contrast and CCD noise sources. Both tri-bar and highly over-sampled imagery are used in the demonstractions.

The tilt scanned solid etalon interferometer has very real advantages in resolving power, throughput and sensitivity over other direct detection techniques, particularly for atmospheric and astronomic spectroscopic measurements. This includes many situations where the measuring instrument is detector-noise limited. These advantages can be exploited in a physically compact, stable, electro-optical system, which imposes no severe tolerances on mechanical mounting, optical alignment or angular scan control. Materials and optical fabrication techniques are available at least for the range 1 to 15 µm which allows for etalon bandwidths of ⪅ 0.2 cm-1, finesse of 50, and peak transmission of 65%. The etalon can be fine scanned over a free spectral range (≈ 10 cm-1) at discrete points in its channel transmission spectrum, or over many hundreds of free spectral ranges, depending on the blocking mode. Some practical aspects of the design, evaluation and use of solid etalons in conventional optical systems are discussed, and the characteristics of a number of such etalons fabricated within the past two years are presented.

An infrared light emitting diode is amplitude modulated at 15 megahertz. The light is optically collimated and transmitted to a cube corner reflector at the distance to be measured. The return light from the reflector is focused onto an avalanche photodiode. The phase relation between the transmitted and the received light is a direct measure of the fractional part of a wavelength from the instrument to the reflector. Multiple frequencies are used to determine the number of whole wavelengths to the reflector. The composite distance is calculated by an on board logic processor and presented on a liquid crystal display. Error is less than ±1 cm at distances up to 1 kilometer. The instrument is economi-cal, lightweight, and rugged for field use. Overall system operation is explained along with special optical and electronic problems and limitations that were encountered.

The infrared scanning data for nondestructive testing are decomposed into three components; global trend, local contours, and noise. Methods are proposed to determine the trend function resulting from surface curvature and surface emissivity changes. The contour function is shown to possess isotherm features which permit the use of pattern recognition to detect structure defects. Data discrimination methods are also presented to identify data as to its implications. As a demonstration for application, two case studies are presented that include analysis for data without either contour or trend component.

The theory and techniques of radiometric calibration, as applied to instruments used to characterize remote target sources, are not well understood by many engineers and physicists engaged in measurement programs. This invited tutorial lecture is designed to show that the correct interpretation of field data is dependent upon an understanding of the theory of calibration. The instrument must be qualified in four nearly independent domains: (1) field of view, (2) spectral bandpass, (3) time, and (4) polarization.

An educational film intended for engineers and scientists, Visions in Infrared reviews basic infrared physics and technology as they are used to solve problems in diverse industries. Infrared energy is naturally emitted by nearly all objects in our environment but our natural ability to sense this energy is very limited. Infrared technology extends these limits so that this portion of the electromagnetic spectrum, just beyond the visible, can be made usuful in many ways. There are several basic components of the infrared system which can be manipulated in order to meet various measuring requirements. These are: object, atmosphere, lens, scanning mechanism, limiter, detector, and data processing. By analyzing and then designing the infrared system around these parameters, measurement problems can be solved in many industries. Basic black and white, portable thermal infrared imaging systems are used in the building, electrical, steel and petrochemical industries. Line scan systems are used for product control and fault detection in process industries. More sophisticated imaging systems employing complex data processing are used in manufacturing development and aerospace research.