We have studied the following problem: An image of a ground scene drifts over a mosaic sensor at a constant drift velocity; given the sensor output at one time, develop an algorithm to predict the sensor output at a nearby time. Such an algorithm allows us to compensate for drift of the background scene between frames of data from the sensor. The mathematical basis of our algorithm is an expansion of the continuous physical radiation intensity on the sensor in terms of the digitized sensor output; the process can be viewed as a generalized interpolation procedure that gives rise to a time-dependent spatial filter with one adjustable parameter. The usefulness of drift compensation in background suppression is evident; for example, we can form conventional first or second difference plots using drift-compensated frames, which should yield quite small differences. If a fairly rapidly moving target is present in the scene it is not suppressed to the same extent as the background, so the ratio of target to background is increased in a difference plot. We have simulated a series of experiments on background suppression using our drift compensation algorithm. Performance has been studied for various values of drift velocity, target velocity, sensor noise, and the adjustable parameter of the algorithm. Our conclusion is that background suppression is in fact much greater with drift compensation than without, based on first and second differences; depending upon the target velocity, drift velocity, and sensor noise that one must deal with, it appears possible to achieve about 1 or 2 orders of magnitude improvement.

Jitter induced clutter leakage in a staring sensor depends on the spatial gradients of background radiance, the detector footprint, and the line-of-sight-jitter frequency characteristics. The clutter problem is very severe when there are sharp radiance gradients or edges in the scene. Clutter leakage models which describe the background by a spatial power spectrum underestimate clutter leakage because they lose the edge information. The model developed in this paper relates clutter leakage to background radiance gradients and the sensor characteristics. The distribution of clutter amplitudes is not Gaussian (even for Gaussian jitter and spatially Gaussian backgrounds); extreme values occur much more often than predicted by PSD analyses. These extreme values affect sensor threshold levels and the associated system data rates. An effective "jitter equivalent angle" is derived for the sensor which is independent of the background. Analysis of Skylab photos in the visible and near IR spectral regions indicates radiance gradients are approximately exponentially distributed and the RMS jitter clutter leakage is proportional to the footprint size raised to the 1.5 power.

This paper discusses the value and importance of infrared measurements programs. Infrared measurements programs are essential to efficient design and development of infrared surveillance systems. Such measurements programs are strongly related to system requirements as well as system technology; and together, these three form the basis for future systems development. These measurements programs provide data to explain and validate phenomenological processes that impact past and current systems. In addition, measurements programs provide information in support of data processing developments and guide the development of advanced technology for infrared systems.

Infrared Multispectral Linear Array (MLA) pushbroom scanners are being developed for NASA's Advanced Land Observing System (ALOS) for the late 1980's to mid 1990's. Pushbroom scanners offer high spectral, spatial and temporal resolution, and high reliability through design simplicity. They use integral chopping and calibration. They require no moving optics. They are lighter, simpler and more compact than their electro-mechanical predecessors. Infrared hybrid focal planes under development for MLA instruments require less power and less space radiative cooling per channel than current LANDSAT sensors. It is anticipated that pushbroom's increased signal integration time across a ground element will provide greater sensitivity and discrimination of the earth's resources. For all of these reasons NASA has selected pushbroom scanners for future ALOS missions.

Analytic models of technology development risk allow the use of powerful numerical optimization techniques earlier than usual in the design of advanced systems. Goal programming is used to find preliminary designs with the best performance-to-cost ratio for a given development risk budget. The advanced technologies that are allocated the greatest portions of this risk budget are the most critical. The application of this approach to space-based infrared step-stare sensors is discussed.

Spatial radiance variations, when combined with sensor or scene motion, have been recognized as a significant source of clutter for staring infrared surveillance sensors. In this paper, data acquired using the NASA Daedalus multi-spectral scanner is examined. On three flights of this airborne high resolution and large extent sensor system, a variety of earth background scenes was collected. Significant spatial radiance variations were measured in mountainous and agricultural earth backgrounds. Data was also collected to allow quantification of the radiance gradient at important interfaces such as between cloud and terrain.

A series of line by line source and background infrared simulation calculations have been carried out in the 4.3 m spectral region in order to identify candidate spectral bands for study using balloon and ultimately spaceborne sensors. Source signatures are presented in terms of apparent radiant intensity produced by a volume of hot CO2 located at altitudes ranging from 0 to 20 km as observed from altitudes of 30, 44 and 100 km. Backgrounds, including terrain, clouds and atmospheric emission have been calculated and are presented both spectrally and as inband radiant intensity. A cursory discussion of non-LTE atmospheric emissions occurring above 60 km is presented and the feasibility of looking up from a balloon borne platform to observe these emissions is addressed. A comparison of source and background signatures is given together with a discussion of the band selection process.

It has been qualitatively demonstrated that the surface currents induced by incident electromagnetic radiation produce I2R heating detectable through thermographic techniques. This paper presents the progress to date toward obtaining quantitative comparisons of known surface current amplitude distributions with those obtained through infrared thermographic analysis. Data for correcting for the directional dependence of IR emission from various surfaces is given, a method of digital analysis of the thermographic data is discussed, and an actual thermographic determination of the surface currents on a square flat plate is presented. These experimental results represent a necessary step in the effort of infrared detection and measurement of the current amplitude distributions on complex shapes.

Effects of nuclear radiation on GaAs emitting diodes have been studied in various investigations. These studies included both devices in which the IR radiation was emitted from the N-side and devices in which the IR radiation was emitted from the P-side. In the references cited the devices were heavily doped with various dopants and the junctions were located approximately 20 μm below the semiconductor surfaces. Measurements following γ-ray irradiation indicated in all cases small shifts (1-4 nm) in peak wavelength of emission towards shorter wavelengths, with the amount of shift depending on the specific impuritiesl. This led to a hypothesis that interaction of nuclear radiation-induced-defects with impurities plays a role in the spectral shift. Other effects of the irradiation were to decrease slightly minority carrier lifetime, to attenuate heavily the emission intensity of the diode emitters, and to increase slightly the forward I-V slope.

Four Stirling cycle mechanical refrigerators are continuing to provide cooling to two gamma ray detector instruments after over 860 days in orbit. These units were developed jointly by North American Philips Laboratories and the Johns Hopkins University/Applied Physics Laboratory and placed into orbit on 24 February 1979 aboard the P78-1 spacecraft. The four units have demonstrated between 4,700 to over 16,000 hours of unattended operation and represent a major breakthrough in the lifetime capability of mechanical refrigerators.

Of various concepts (both staring and scanning) which have been proposed for the detection of dim moving targets from space, many have sensitivity limitations arising from smear - induced drift which causes displacement between frames of data. A multi-fan pushbroom scan concept recently proposed by W.K. Davis has an advantage over some other scanning concepts in that the frames of data can be processed by the same high performance algorithms applicable to staring sensors. The displacements caused by smear in this technique are discussed as well as three simple techniques for eliminating the displacements. The principal technique of the three which compensates for most of the displacement is a slow controlled yaw of the spacecraft. An example is presented in which the uncorrected smear displacement is 800 m while the corrected smear displacement is 0.8m, for a smear reduction factor of 1000.

Recently the British unveiled details of a new Mercury Cadmium Telluride (HgCdTe) "SPRITE" detector that performs time delay and integration within the material itself. This paper introduces the concept, analyzes and explains the detector's unique features, and presents the results of an experimental investigation, in this country, of both the device and a system utilizing it. Consideration has been given to such system implications as the limitation on the number of detector elements that can be used, power, and scanning speed requirements. Based on the experience and results obtained operating a SPRITE device in a modified discoid system, an optimized TV compatible FLIR system is described and performance predicted.

Temporal variations in a given background scene must be taken into account in evaluating the performance of infrared and microwave radiometric sensor systems. Some common examples are diurnal and seasonal temperature variations, changes in cloud patterns, precipitation and its accompanying effects on terrain, such as snow, ice, and water cover. As part of our Sensor Data Test Program, we propose to generate sets of simulated data frames chosen to be statistically representative of the temporal variations for particular background scenes. The simulation procedure utilizes parametric models of the changes in Question. Generation of the different simulated data frames is accomplished by varying the model parameters according to some specified statistical procedure. The present paper deals with the modeling of scene variations. In particular we describe our methodology for parametrizing the effects of scene variability by a statistical analysis of real data frames and present some examples of our results.

Detailed line-by-line computations have been made to assess the utility of balloon-borne sensors for determining the backgrounds that will be encountered by space-based 4.3µm surveillance systems. In this spectral region, the atmosphere becomes opaque at the CO2 line centers in a short distance everywhere in the atmosphere below an altitude of 100 km, whereas the atmosphere is quite transparent between lines down to around 25 km altitude. Thus radiation intercepted by a space-based sensor with a spectral bandwidth greater than a few Doppler line widths will originate from a variety of levels in the atmosphere, where the physical mechanisms leading to background variations or clutter may be quite different. Our calculations indicate that down-looking measurements from 30 km (a typical balloon altitude) will adequately determine the clutter originating below the balloon. On the other hand, the determination of clutter above the balloon by an up-looking sensor will be much more uncertain because radiation from this region will reach space with less attenuation than it will experience traveling down to the balloon. Quantitative results representative of various spectral locations in the 4.3-μm band of CO2 will be presented.

A method of calculating the self-radiance of the sky based on LOWTRAN-4 computer code is described. The method is a significant improvement on that included as an option in LOWTRAN 4 itself as a result of two modifications: a) Our method, unlike the one included in LOWTRAN 4, takes into account the radiance scattered into the line of sight. b) The model of the atmosphere in the computer code must be divided into a certain number of layers each one having approximately uniform conditions. Our method uses a correct optimal division. Consequently, our method gives a better agreement with the experimental data, especially for long optical paths in the lower layers of the atmosphere.

Atmospheric emission measured at 2.7 µm by the SPIRE earth limb rocket experiment under sunlit conditions has not been fully understood to date. While initial analysis showed this emission to be different from the hydroxyl spectra observed on the night side during the same experiment, the authors were only able to speculate on the processes responsible. In this paper, we develop a model of fluorescent CO2 hot band emission to explain approximately 40% of the measured SPIRE data. In addition, we include the results of two other models to show the contributions required from CO2 and H20 resonant fluorescence.

This paper discusses the conceptual design of an all solid-state linear array wide field-of-view spaceborne meteorological sensor optimized for launch and use during the shuttle era. The instrument is designed to obtain synoptic meteorological imagery in the visible and infrared bands. The requirements of wide-angle, minimal glare, constant ground footprint requirement is implemented in the visible band with multiple telescopes and electronic switching of CCD detector areas. The wide-angle longwave infrared channel uses a single optic with a continuously varying focal length (constant ground footprint) as a function of scan angle and a focal plane with a refractive acousto-optic chopper and uncooled linear detector arrays. The instrument is configured for cost effective shuttle launches.

A comparison of experimental atmospheric transmittance with the predictions of the LOWTRAN 4 computer code requires accurate knowledge of the total water vapour content along the optical path. This quantity was measured, in terms of the integrated absorption of the 1.15 μm water vapour band, along distances of 5.6 and 7.1 km at sea level. Both the LOWTRAN 4 and the strong Goody models were used to deduct the water vapour content from the integrated absorption. The results were compared with experimental data obtained from conventional wet-and-dry-bulb thermometry. It was found that the data for this band in the LOWTRAN 4 model gives poor agreement whereas the use of the strong Goody model results in a considerable improvement.

Here we briefly review non-LTE mechanisms for high-altitude atmospheric infrared background emissions near 4.3 µm. We concentrate on non-LTE mechanisms for CO2 4.3 µm emission. In the daytime this includes excitation by absorption of sunlight in the 4.3 and 2.7 µm region by CO2, followed by re-emission near 4.3 µm. In the nighttime, transfer of vibrational excitation to CO2 from excited OH via N2 as an intermediate plays a major role. In the auroral case, vibrational excitation of N2 by precipitating electrons is transferred to CO2 and results in intense 4.3 µm aurora with a time constant in the range of 3 to 30 min. In all cases multiple absorption and re-emission of 4.3 µm photons by CO2, and multiple collisional transfer of vibration quanta back and forth between CO2 and N2, plays an important role. Some examples are given of validation of these effects against high sensitivity data obtained in the infrared measurements programs of the Air Force Geophysics Laboratories (AFGL) via rocketborne sensors. Also, some evidence from the AFGL program for a second 4.3 µm auroral mechanism, weaker but faster than the CO2 mechanism, is discussed. Predictions of auroral nadir and earthlimb structure are also given.

A conceptually simple high-speed infrared (IR) zoom lens system has been designed to operate in the 8-13 μm wavelength region for the detection of missile signatures. Even though the optical system is designed to provide high resolution throughout the 3 : 1 zoom range at a large relative aperture, it is extremely lightweight and compact. The zoom concept has been derived from first order optical principles which will be presented as the starting point of the optical system design. The use of the symmetry principle for aberration correction will be discussed. Paraxial ray trace was used as an aid in establishing lens powers and groupings in the initial layout. Considerations which governed material selection will also be discussed. The zoom system consists of six lens elements including a field flattener near the image plane. The total glass weight is only 172.4 grams and the length is 161.79 mm. There are two moving lens components linked together with a cam to provide mechanical compensation. The detail design was accomplished through the use of a computer optimization program. The 1 mrad image resolution requirement is achieved throughout the zoom range. Performance data will be presented and tolerance considerations will be discussed.

A very simple telescope is described that consists of a parabolic mirror, a small spherical mirror, and a single germanium lens. This three-element telescope is unobscured, is corrected for spherical aberration, coma, astigmatism, and Petzval curvature, and has stray-light rejection features. The good aberration correction makes it suitable for covering a substantial field of view on a flat image surface. The stray-light rejection features are: no obscuration, an aperture stop, a field stop, and a Lyot stop. The key to this new design is the novel use of two separate optical axes in the same system. The parabolic mirror and the spherical mirror have the same optical axis, but the axis of the lens is displaced and parallel. The theory of the design will be explained.

As solar arrays for space applications become larger and larger, the circuits and solar cells become thinner and more delicate. Now, with the advent of folding and unfolding reusable arrays, the integrity of the array becomes more critical. A number of infrared techniques have been developed to assist in this area. First, an 8 - 13 μm infrared scanner proved to be an excellent way of identifying nonfunctioning or defective cells. The same scanner with optical modifications could also detect defective cell bonds. Next, a near infrared device has been adapted to both sense and control cell-to-circuit bonding in real-time as well as provide product assurance documentation on each bond. A fourth application utilizes a videoized infrared microscope which looks through the silicon showing normally invisible cracks in the silicon as well as bond footprints. The combined infrared techniques make it possible to not only assure a high integrity durable array to start with, but provide the means of nondestructively checking arrays and also detecting and identifying the bad cells or bonds for refurbishing used arrays.

The status of a technology program to evaluate existing infrared detector arrays and to develop improved ones for low-background astronomical applications is described. For applications such as the Shuttle Infrared Telescope Facility (SIRTF), arrays that cover as much of the 1-1000 μm range as possible are of interest. Low-background test results for 2 x 64 Si:Bi charge-injection-device and 1 x 20 InSb charge-coupled-device arrays are included. As a result of our testing, we plan to develop improved, astronomy-optimized extrinsic silicon arrays in both linear and area formats. Efforts to develop accumulation-mode MOSFETs specifically for liquid helium temperatures, and cryogenic amplifier and multi-plexer circuits, are discussed.

Experiments have been conducted to record infrared images using wax films as photographic material. The thin films used which were prepared by Dip Coating Method have been deposited on glass plates. As indicated in a previous paper, the thickness of wax films has been chosen to be approximately 0.6 μm. An investigation has been conducted to study the possibility of lowering the intensity threshold needed to photograph infrared images. Good results have been obtained when the photographic plates are preheated; so, the 0.4 J/cm2 required previously is now reduced. Moreover infrared images obtained are seen as surface deformation of the recording medium and, by using a conventional photographic system, the final picture is achieved under an appropriate illumination.

Wavelength tuning of LEDs is known to occur through changes in temperature and application of pressure or magnetic fields. All such tuning techniques are based upon changes in forbidden energy gap Eg. Here, a simple general spectral tuning technique, not based upon bandgap changes, is suggested and shown experimentally to be feasible. The technique, appropriate for shallow junction surface-emitting LEDs, is repeatable, controllable, reversible, and appears to be completely non-destructive.

Measurements of the far-infrared bidirectional reflectance distribution functions (BRDF) of four samples of Martin Black coating and one sample of gold-coated aluminum from the telescope to be flown on the Infrared Astronomy Satellite (IRAS) are presented. At incidence angles near 35°, Martin Black is a diffuse reflector at wavelengths as long as 36 μm. However, by 112 μm it has become quite specular. The gold coated aluminum sample from the IRAS sunshield has a visible grain which causes a strong diffraction enhancement of the BRDF at large nonspecular angles. This enhancement from the sunshield will increase the stray light level inside the telescope.

Infrared measurements of targets and backgrounds are made from five different platforms--ground, aircraft, balloons, rocket probes, and satellite. The advantages and disadvantages of each platform are discussed, and the measurement goals that would motivate the selection of one over another are assessed.