Based on temporal and spatial characterizations of IR background clutter, an optimal algorithm, which in essence, is equivalent to a maximum likelihood test, is derived for clutter suppression and target detection. The algorithm is adaptive in that the algorithm parameters (temporal and spatial correlations of the background clutter) could be continually updated if desired. The algorithm also makes use of the a priori knowledge of target intensity, whenever possible. Preliminary simulation results indicate that background clutter can be sufficiently suppressed so that the detection of low intensity targets (signal-to-noise ratio of 1) can be achieved.

A mosaic sensor on a moving platform staring at a fixed location sees a background motion on all detectors except the one at the stabilized location. This relative motion between the footprint and the structured background produces a noise factor in the system which can be comparable to the other noise sources. The effects in a surveillance sensor in low-altitude orbit is shown and a method of displaying a time history of the signal-to-noise ratio is demonstrated.

A satellite-borne staring mosaic sensor has a line-of-sight that is stabilized on a fixed earth point. As the satellite passes near this point, detectors not on the line of sight are subjected to noise produced by apparent background motion. This motion is produced by footprint shrinkage, change in aspect angle, and earth rotation. The motion is affected by satellite orbit parameters, earth location of the observed scene, and detector location in the sensor focal plane. Additional motion produced by satellite instability may increase these effects or negate them depending on random direction. Equations are presented which enable the instantaneous description of the complete state of the focal plane scene. Samples of dynamic detector footprints, views of changing earth scenes, and graphs of background velocities are included. Effect of spacecraft instability is presented in terms of upper and lower bounds on the velocity magnitudes.

This paper examines the basic equation for clutter leakage in an optical system and discusses approximation techniques for rapid estimation of noise-equivalent target as a function of background PSD, optical system parameters, range and rate of motion of the sensor FOV relative to the background. Approximations which were developed for the conventional single-break-point PSD with a slope of -12 dB/octave, with a system using frame-to-frame differencing over an extended range of FOV motion rate are included as an appendix. A new method is derived, valid for low rates of FOV motion and a more general PSD, which can be approximated by a broken-line Bode plot. This method is extended to cover Nth order frame differencing and two-dimensional FOV motion, with the background viewed from a direction other than perpendicular to the surface. Given a specific optical system observing a specific background with any typical PSD, clutter leakage will display a dependence on FOV motion rate proportional to VN, where V is the motion rate, and N is the order of frame-differencing used for clutter rejection. This result is independent of the shape of the PSD curve for usual PSD's and system parameters.

The key benefits of charge-coupled devices in space-borne scanning point-target detection/location systems are the potential impact for power, size, weight, and cost reduction. These advantages accrue from the capability for integrating several CCD signal processing functions onto a single substrate. This paper describes results of an effort which successfully demonstrated the monolithic integration of key CCD signal processing functions for a representative high-performance scanning surveillance sensor. The principal information required by the sensor for this application is the magnitude and two-dimensional centroid estimation of point targets. The key functions provided by the CCD signal processor are delay-and-add and focal-plane formatting for two-way scanned sensor, multiplexing, and two-dimensional analog centroid filtering.

The Balloon Altitude Mosaic Measurements Program is designed to make temporal, spatial, and spectral measurements of earth backgrounds in the infrared. The measurements obtained from BAMM will support another SAMSO development, the Mosaic Sensor Program. The measurements will be made from a stabilized balloon-borne platform at 100,000 ft. altitude. Scenes to be viewed are background sources such as cirrus clouds, high altitude lakes and snowfields, ocean effects (glitter, land/sea interface), and temporal buildup of cumulus clouds. Emphasis will be on obtaining these measurements at low sun scattering angles. Instruments consist of a 2.7 micrometer radiometer, a 2.5-5.5 micrometer interferometer, and a TV camera for real time viewing and pointing. Four-by-four element mosaic arrays will be the focal planes for the radiometer and interferometer. Per element resolution is 1 kilometer at nadir. Seven flights are planned, each approximately ten hours duration, beginning in January 1978.

An optical method of suppressing an imaging system's response to a slowly varying background interference is described. The method involves masking the photodetectors with a photochromic plate and a model for this system is developed. The photochromic mask is shown to be equivalent to an optical Automatic Gain Control (AGC) device. The time response of such a system is developed and simulation results are presented that demonstrate the feasibility of this approach.

The development of IR detectors will be traced from early polycrystalline film detectors to single crystal intrinsic detectors prepared from III-V compounds,as well as extrinsic detectors prepared from Ge and Si to the most recent detectors prepared from the ternary compounds HgCdTe and PbSnTe. The characteristics and methods for changing them to fill particular needs will be discussed.

Measurements have recently been made of the signal and noise characteristics of extrinsic photoconductive silicon detectors. The measurements were made at several background levels, bias voltages and detector operating temperatures. Data are shown at modulation frequencies as low as 0.01 Hz, operating temperatures as low as 2.5K and background photon flux densities down to 8 x 107 photons/sec-cm2. Data on the temporal characteristics of the detector signal are presented. In addition, some interesting data on "spontaneous noise spikes" are also shown.

This paper will survey and review the present state-of-the-art and assess the ultimate potential of mercury-cadmium telluride (HgCdTe) infrared detector focal plane technology.

Large focal plane detective assemblies are an important component of many new infrared surveillance or imaging systems. These focal plane assemblies comprising large mosaics or long linear arrays of lead salt or crystal detectors are being integrated into new and more sophisticated systems which are in turn demanding more range and better resolution. One area which may hinder achievement of these goals lies in the unwanted effects of electrical or optical crosstalk. This paper suggests some specific measures which may be taken to reduce optical crosstalk in these detective assemblies.

Thermal imaging systems for industrial and military applications have capabilities not envisioned twenty years ago. Much of this rapid growth in capabilities is a direct result of synergistic coupling between system and detector design engineers funded by the United States Department of Defense. In many designs both the detector and the system optical designs have been pushed to levels very near their fundamental limits. It is therefore, advantageous to spell out some of the fundamental limitations on detectors to avoid the needless design iterations which result when only the equations (without boundry values) are manipulated in the quest to meet the system packaging and sensitivity requirements.

Mercury-cadmium telluride (HgCdTe or Hg1-xCdxTe) has emerged over the past fifteen years as the most widely applicable infrared quantum detecor material available today. Highly sensitive photoconductors, photodiodes and MIS (metal-insulator-semiconductor) detectors, achieving in many cases background-limited performance, are now being used in or being developed for a wide range of DoD and NASA sensor applications over the 2-30 micrometer spectral range. This paper is a brief review of the basic principles of operation, the performance characteristics, and the state-of-the-art of HgCdTe infrared detectors. Emphasis is placed on HgCdTe photoconduc-tors and photodiodes. The paper is intended to provide basic information to those who are or who will be incorporating HgCdTe detectors into modern infrared sensors and systems.

Possible system applications of Infrared Charge Transfer Devices are reviewed. It is found that this device technology can have a very significant systems impact. Analyses are performed to calculate the quantum efficiency, quantum yield, frequency response, photoconductive gain, operating temperature, noise and the distinction between parallel and transverse bias configurations of silicon detectors. Tables of silicon detector properties are included. Approaches to the interface circuitry which couples the detectors and the CTD multiplexer are examined. Examples of existing low background and high background IRCTD detector arrays are given.

A significant effort in any research and development program involving large infrared detector arrays is parameter measurement and evaluation. In fact, the major portion of the program cost is in some way involved with measurements. For this reason and because of the acquisition of several programs requiring large numbers of deliverable arrays, a computer based automated data acquisition system has been implemented for the infrared device effort at the Science Center. A Data General Eclipse S/200 computer with two 10 mega byte disks is utilized. Data acquisition from remote locations is effected by daisy chaining as many as fifteen Hewlett Packard multiprogrammer units at 100 foot intervals. Graphical display of the results as well as operator interaction with the program is conducted using Tektronix 4010 series terminals. The new Data General advanced operating system (AOS) allows independently called time sharing operations from each terminal. A Versatec printer/plotter is used for hard copy of the screen image as well as for a line printer. Test programs for current vs. voltage (IV), capacitance vs. voltage, spectral responsitivity, optical area measurement using an automatic blackbody scan and multiplexer video data acquisition programs have been written and implemented. In addition to acquiring the data, the IV test program has a number of optional features. Included is the ability to control stepping of a cryogenically cooled automatic probe station, allowing completely unattended IV evaluation of a 1024 element array. Another important feature of the IV program is the option of addressing individual row and column elements of mated multiplexer/ diode arrays and measuring IV characteristics through the video output. Examples of the use of this system for evaluation of 32x32 PbSnTe and InAsSb arrays will be given.

A SPectral InfraRed Experiment (SPIRE) rocket payload designed to make selective measurements of the sunlit earth limb is described. Two cryogenically cooled CVF spec-trometers and a dual channel photometer will be used to spatially and spectrally map the horizon from 5000Å to 15.5μm. All three sensors have been telescoped with low scatter optics which are capable of resolving an 8 km tangent height at the limb while rejecting competitive terrestial and solar radiation. A coaligned TV camera and two celestial pointing monitors complete the instrument complement. Experiment objectives, instrument and telescope design, subsystem tests, and subsequent modifications are described. As of this date (August 1977), payload integration has been completed with a launch scheduled for late September 1977.

Preliminary results of an infrared survey of the equatorial sky zone (declinations 10° S to 10° N) with U. S. Air Force satellite sensors show that positions of previously unknown infrared sources are measured with an rms accuracy of 4 arc seconds, which is six times better than the best previous infrared survey. The search area per source for further study is thus 36 times smaller, so that identification of the infrared sources with optical objects in catalogs and sky photographs is facilitated, as is reacquisition of the sources with ground-based infrared telescopes. The survey extends the content of near-infrared source catalogs to lower flux densities and adds information at a wavelength not observable from the ground. Objects found in the survey include cool giants and supergiants, long-period and semi-regular variable stars, and sources identified with faint red stars visible on the Palomar Observatory Sky Survey.

The LIR instrument has been developed for the NASA Ames Research Center for use in the 1978 Venus Atmospheric Probe Mission. The mission objectives are to determine the nature and composition of the clouds, the composition and structure of the atmosphere, and the atmospheric circulation pattern of the planet Venus. The The Large Probe Infrared Radiometer (LIR) is a six-channel (3 to 50 μm) internally calibrated radiometer which measures the radiance difference at ±45° to the horizontal as viewed through a single diamond window in the spacecraft. The LIR optical system consists of a unique arrangement of hollow light pipes which optically couple a six element detector/filter array to the spacecraft window while mechanically and thermally isolating the array from the window's harsh thermal environment. A single rotating section with a 45° bend and containing a collimator alternately views up and down through director/extender pipes located adjacent to the diamond window. Light is transferred from the rotating section to a fixed section containing a diamond diffuser to scramble the light. This minimizes asymmetries and improves channel field of view overlap.

A model of the infrared radiance of the zodiacal light is generated which is based on parameters deduced from the visible scattering data and in-situ micrometeorite detectors. Comparison of this model with an infrared spectral measurement indicates that the dust is composed of a dirty silicate material. Detailed calculations of the spectral radiance and the directional variation are presented.

The USAF Satellite Infrared Experiment (SIRE) will offer the opportunity to conduct space-based astronomical measurements. Experiments include formation of star catalogs, the determination of the color temperature of stars and asteroids, and the measurement of extended radiation. In this paper some of the data processing techniques required for these experiments are discussed and evaluated. In particular, tradeoffs in the design of efficient star cataloging algorithms, and a methodology for extracted extended background are discussed. These algorithms are evaluated using simulated data. Performance results for both the cataloging algorithm and the background estimation algorithm are discussed.

An I-SIT television system using a 40 mm S-1 image tube fiber-optically coupled to a 40 mm SIT vidicon tube has been used extensively for astronomical observations in the near-infrared. The camera and data acquisition system is briefly described and the digital picture reduction scheme is illustrated with both spectroscopic and direct imaging data. Observations of the red supergiant star Betelgeuse (α Orionis) are presented that reveal the remarkable extent of the gas shell that surrounds the star. A brief interpretation of these data in terms of mass loss is presented. Planetary observations of Jupiter in the methane band (λ 8900 Å) are also discussed.

This instrument is a new form of non-dispersive gas correlation sensor. It was designed to measure the emission from atmospheric gases in the stratosphere and mesosphere from a space platform. The measurement technique involves the pressure cycling of a sample of the gas to be detected in a small optical cavity through which incoming radiation is passed. The principles of pressure modulation technique and several areas of terrestial applications will be discussed in the paper.

This paper describes an innovative infrared scanning instrument which features a unique display. Through the use of dichroic scanning elements and a light-emitting diode array, this device superimposes an analog temperature "A-Trace" over the visual image of the target being scanned. Instant photorecording is accomplished by means of a Polaroid SX-70 color camera aimed directly through the instrument's reflex sight. The superposition technique provides true registration and correlation between the visible and thermal information. This is unattainable with conventional infrared scanners. Applications of this instrument are reviewed, particularly those related to energy and resource conservation.

Two (2) US Air Force-owned engineering development models of the AN/AAD-5 Infrared Reconnaissance Set were flight tested at Wright-Patterson Air Force Base during 1971. After a successful flight test, the next generation of this improved infrared sensor was built to undergo extensive qualification (i.e., bench) testing. The Environmental Protection Agency requested the use of the original models and in mid-1976 took possession of the sensors and peculiar support equipment. The equipment was slightly modified and adapted to a civilian aircraft, in which it is being used successfully to obtain data much needed by the Environmental Protection Agency.

The Strategic Air Command (SAC) used overhead infrared reconnaissance imagery to detect heat losses from the roofs of buildings. The effort was highly successful and revealed not only individual heat losses but also systemic losses in entire classes of buildings. On-the-spot inspections of buildings experiencing heat losses confirmed the accuracy and reliability of overhead infrared as a heat loss detector.

Display flicker has been an inherent characteristic of 3 to 5 micron lead selenide Forward Looking Infrared (FLIR) systems because the detector time constant ultimately limits the mechanical scan rate. In some systems, flicker has been reduced by increasing the frame rate from 15 to 30 frames per second (FPS); however, objectionable flicker is still apparent at the display edges due to the triangular scan used. This paper presents a digital scan converter technique which produces a completely flicker free display while maintaining the 15 FPS mechanical scan system rate. The system also enables a stop-action mode of display.

A four-bar infrared test target has been built to test the feasibility of using perforated ambient temperature plates for the four bars instead of the customary plates operated at temperatures different from ambient. Six different sizes of four-bar arrays provide six different spatial frequencies. Front and back arrays of perforated plates are moved relative to one another by a motor drive to expose more or less of a sky reflector backplate, thereby producing a varying apparent temperature differential between the bars and their interstices. The target system also features a radiometric monitor which mechanically servos the bar patterns to compensate for changes such as dust or clouds. Qualitative tests with infrared imaging systems show satisfactory bar patterns which disappear when the perforations are closed. Quantitative tests show that differential temperature accuracies of about one tenth of a kelvin can be attained.

This paper describes an unusual tuning fork chopper in the development of which several significant advances were made. The specific application was in an infrared radiation experimental package on a deep space (interplanetary) 'vehicle. However similar devices can be applied generally in other optical systems, wherever it is desired to modulate incoming radiation while sequentially directing the beam to two or more instruments. Radiation need not be in the infrared portion of the spectrum but can be any wavelength capable of being reflected by a mirror. The basic requirement for the infrared package was a device which could modulate the incoming radiation by chopping a direct path to one instrument and provide a reflected path of image quality to a second instrument. The tuning fork device described hereafter accomplishes this dual function. It is basically a tuning fork chopper which, in addition to the usual modulating function, also serves as a beam splitter. In place of the usual blackened vanes this chopper carries a pair of vanes which have a high quality mirror surface. Because the radiation level would often be very low it was essential that very precise control of the aperture be maintained and that heat input to the vanes be avoided. Also, reactive forces to the experiments' optical bench had to be minimized and the device's magnetic field shielded. The unit described herein is basically similar to Bulova's proprietary Type L40 tuning fork choppers with modifications to meet the optical requirements and operation in a deep space environment. It was made for Texas Instrument Corporation for incorporation in an infrared interferometer-spectrometer package in the Mariner space vehicle for the Jupiter/Saturn/Uranus mission. The paper is devoted primarily to the problems peculiar to the application and to the solutions which enabled the unit to meet the unusually rigorous demands of both the performance parameters and the environment.

An infrared automatic landing system for guiding a mini remotely piloted vehicle (RPV) into a net has been designed and conceptually tested. The system consists of a ground-based pulsed GaAs laser transmitter illuminating a cooperative RPV, and a ground-based tracking receiver sensing the position of the RPV. This position information is telemetered back through the control link to the RPV to guide it down. A key element in the system is a state-of-the-art tracking receiver that has no moving parts, but uses a holographic field lens to do the real-time signal processing. The receiver, besides providing position data, also gives ranging information. The complete landing system is packaged in a battery operable box critically placed on the ground at the landing area.

The use of color infrared photography in stress detection in forestry and agricultural applications is well established. In the ecological succession process, the dominant vegetation population is deteriorated because of a change in the local environment. This change results in the proliferation of a species or community better suited to the altered environment. Stresses on the health, vigor and productivity of the succeeded plant population are early signs of the environmental alteration. Visual interpretation of aerial color infrared photography of a south Louisiana swamp determines where an ecosystem succession may occur by monitoring the advance signs of stress invisible to conventional films. The digital data from bands five (0.6-0.7 micrometers) and seven (0.8-1.1 micrometers) of LANDSAT earth orbiting satellite is used to characterize and compare the spectral signatures of known areas of environmental alteration in the swamp lands with areas of unaffected swamp vegetation. The image classification capability of a Comtal-Varian Interactive Image Processing System uses the spectral signatures of the test areas as a search tool for locating other potential succession areas over a wide region.

A method is presented to determine the surface-temperature distribution at each point in an infrared picture. To handle the surface reflection problem, three cases are considered that include the use of black coatings, radiation shields, and band-pass filters. For uniform irradiation on the test surface, the irradiation can be measured using a cooled, convex mirror. Equations are derived to show that this surrounding irradiation effect can be subtracted out from the scanned radiation, thereby relating the net radiation only to emission from the surface. To provide for temperature measurements over a large field, the image-processing technique is used to digitize the infrared data. The paper spells out procedures that involve the use of a computer for making point-by-point temperature calculations. Finally, a sample case is given to illustrate applications of the method.

An ir spectrometer, used to obtain measurements of faint atmospheric emission spectra from a rocket carrier, is described. The sensor scans the 2.07 to 5.47 μm spectral region at the rate of 2 scan/s. The spectral resolution of the sensor, which employs a circular variable filter (CVF), ranges from 1.0 to 3.0%. The entire optical subsection, indium anti-monide detector, CVF, silicon lens, baffle, and removable cover are cooled below 80° K in a high-vacuum Dewar system. The noise equivalent spectral sterance [radiance] of the spectrometer at 5.3 μm is 1.93 x 10-10 (W cm-2sr-1μm-1).