The problem of suppressing the effects of line-of-sight (LOS) jitter in staring mosaic sensors is approached from the viewpoint of both real time and postprocessing of the corrupted focal plane data. Fundamental limits on the joint observability of LOS motion and spatial scene gradients are established as a function of the level of sensor and background characterization information assumed to be available. It is shown that although separability cannot be assured in most cases of interest, the effects of jitter can be estimated and synchronously subtracted from focal plane data. Simulation results are presented which demonstrate signal to noise improvements in excess of a factor of ten.

A novel optical technique for improving the performance of focal plane staring arrays by increasing the fill factor ratio is described. The specific mosaics considered are 64 x 32 and 128 x 64 Schottky barrier infrared detectors with charge coupled devices (IRCCD) made from monolithic silicon. The video enhancement is accomplished by means of a refracting silicon faceplate that redirects focused image irradiance from nonsensitive CCD areas to the infrared detector elements. Operational theory and design parameters for this unique faceplate construction are detailed. With the optimum faceplate configuration installed at the IRCCD front surface, a sensitivity increase of at least .200 percent is predicted from the analysis presented here.

Infrared radiometers have been used to make time-resolved emission measurements of shocked explosives. Instruments of moderate time resolution were used to estimate temperatures in shocked but not detonated explosives. The heterogeneity of the shock-induced heating was discovered in pressed explosives by two-band techniques, and the time-resolved emittance or extent of hot spot coverage indicated a great dependence on shock pressures. Temperatures in moderately shocked organic liquids were also measured. Faster response radiometers with 5 ns rise times based on InSb and HgCdTe photovoltaic detectors were constructed and tested. Preliminary data on reactive shocks and detonations reveals a resolution of the heating in the shock wave and the following reaction.

This paper discusses the techniques utilized during automated testing of Z-technology modules for mosaic focal planes. The testing includes continuity and isolation resistance measurements on both layers and modules, and functional tests of the Signal Processing Chips as they are wirebonded to the modules. The criteria for layer selection, empirically derived, is presented. Test results are presented and their impact on product development are described.

To support the development of advanced infrared remote sensing instrumentation using line and area arrays, a test facility has been developed to characterize the detectors. The necessary performance characteristics of the facility were defined by considering current and projected requirements for detector testing. The completed facility provides the desired level of detector testing capability as well as providing ease of human interaction.

In the measurement and characterization of the performance of infrared and visible focal plane arrays, the determination of the detailed spatial response of individual detectors as well as the entire array can be extremely important in many electro-optic sensor applications such as the detection of targets in the presence of clutter and passive acquisition and tracking. This paper describes a computer-controlled flying spot scanning technique for the measurement of detailed focal plane detector responses as well as detector-to-detector cross talk and spurious responses. The technique uses a computer-controlled flying spot scanner and online data processing. A simple deconvolution is used to remove the known temporal responses of the detector and electronics followed by a two-dimensional decorrelation of the blur spot from the output signal to obtain the focal plane spatial response. As a natural result of this process the individual detector MTFs can be obtained. This technique has been implemented in a low-background focal plane test facility, which is also described. Several examples of actual test data are shown to demonstrate the use of this spot-scanning facility and its utility as a diagnostic tool.

A measurement program currently underway at Calspan to determine the excitation cross section (σ*) for the interaction of CO2 and H2O molecules with atomic oxygen is described. A shock-tube technique is used to drive a monoenergetic stream of atomic oxygen, in a helium plus argon diluent, into a jet of target gas injected normal to the incident beam. Subsequent radiation resulting from the collisional interaction of the highly expanded beams is observed immediately downstream using a filtered indium antimonide detector. With this experimental technique, measurements have been obtained for interaction velocities in the range of 4.5 to 7 km/sec.

Determination of the infrared irradiance caused by stars and other objects outside the earth's atmosphere by means of sensors located within the atmosphere requires correction for atmospheric effects. Subtraction of the path radiance is often inherent in the sensor design. However, determination of the atmospheric transmittance is more difficult, frequently requiring auxiliary measurements of profiles of species concentration, temperature, and pressure along the optical path. A procedure has been developed for determining the atmospheric transmittance, without reference to atmospheric profiles, from the measured path radiance augmented by surface meteorological observations. The dependence of the effective atmospheric radiating temperature on elevation angle for a given sensor band can be described by a function of elevation angle in which the parameters are determined from surface observations. When the effective radiating temperature of the atmosphere is known, the transmittance is obtained from the emissivity defined by the ratio of the observed path radiance to the Planck function for the effective atmospheric temperature. This algorithm, which is useful only for clear conditions in the infrared spectral windows, has reproduced, in test situations, the transmittance computed with models such as LOWTRAN to within 10% for all portions of the sky with elevation angles greater than 10 deg.

Phenomenological descriptions of radiance distributions can be an important input for the modeling of infrared background scenes. The resulting models can be used as the basis for generating synthetic background scenes for the purpose of testing target discrimination and navigation algorithms in cases where real data are unavailable. Statistical analyses of thermal infrared images of ocean, clouds, and various types of terrain have been carried out in the context of such modeling work. The images were obtained by the NASA/Ames Daedalus multispectral scanner. Special emphasis is placed on the spatial correlation structure of the radiance distributions for the various background types. The results are compared with the predictions of an exponentially correlated Gaussian random walk process.

The extensive use of advanced composite materials on aircraft has increased the need for improved inspection techniques. Presently, graphite composite structures for high performance military aircraft require extensive ultrasonic and X-ray inspection for the detection of porosity, delaminations and disbonds. Thermographic inspection offers the potential for a lower cost alternative to these techniques. Much of the work on the application of thermographic techniques as an alternative to the above means of inspection has been qualitative and limited to laboratory use. The transient thermal response of graphite composite structures has been shown to be useful in detecting porosity, delamination and disbonds, and the use of image processing simplifies operator interpretation of the resulting data. This paper describes further research on this subject and proposes systems for production use and field inspection of advanced composite structures.

With the development of the new super strength lightweight composite materials, flaw and void detection in the various layers have become of major importance. Special infrared imaging techniques have been developed to show these voids. Included in these nondestructive methods are active steady state, active pulsed, and fast recording with slow playback of infrared images. Emissivity correction techniques have also been considered. Considerable time can be saved by using an imaging system since the size and shape of a defect or void is known at a glance. With video recording, documentation is achieved and further analysis is also possible without tieing up the part. Growth or changes of marginal flaws or voids can be traced during the manufacturing process, noting if they increase to the point of nonacceptance. An 8-13μ infrared scanner compatible with a video recorder and a line integrator proved most effective. Colorizing the image also made the flaw visualization easier.

The Near-Infrared Mapping Spectrometer (NIMS) is one of the science instruments in the Galileo Mission, which will explore Jupiter and its satellites in the early-1990's. The NIMS experiment will map geological units on the surfaces of the Jovian satellites, characterize their mineral content; and for the atmosphere of Jupiter, investigate cloud properties and the spatial and temporal variability of molecular abundances. All the optics are gold-coated reflective and consist of a telescope and a grating spectrometer. The balance of the instrument includes a 17-detector (silicon and indium antimonide) focal plane array, a tuning fork chopper, microprocessor-controlled electronics, and a passive radiative cooler. A wobbling secondary mirror in the telescope provides 20 pixels in one dimension of spatial scanning in a pushbroom mode, with 0.5 mr x 0.5 mr instantaneous field of view. The spectral range is 0.7 - 5.2μ; resolution is 0.025μ. NIMS is the first infrared experiment to combine both spatial and spectral mapping capability in one instrument.

At the Barstow 10MW Solar Thermal Pilot Plant, water is converted to high pressure steam by concentrated solar radiation. The design of the elements in which the boiling takes place makes them vulnerable to blockage by particulates contaminating the circulating water. Concern over the potential for heat damage to blocked boiler elements has led to the development of a remote optical monitoring system for use at the Pilot Plant. The system employs a telescope and infrared vidicon to detect the increased blackbody radiant emittance produced by an overheated element. An image is provided with spatial and thermal resolution sufficient to detect and identify a single blocked element. Design considerations for such a system are discussed, as are performance at the Pilot Plant and possible extensions of the system to more sophisticated pyrometric tasks.

Synthetic background scenes can play a significant role in the development of space surveillance systems and autonomous navigation. They can be used to test the performance of proposed target acquisition and tracking algorithms, to evaluate the robustness of navigation algorithms with respect to temporal scene variations, and to investigate the scope of on-board data processing requirements. They can provide a more thorough and systematic evaluation of the relative performance of competing algorithms for a greater diversity of terrain backgrounds, environmental conditions, and viewing geometries than real data. Moreover, their use requires no costly commitment to hardware construction and flight programs. We describe a comprehensive program for the generation of Monte Carlo sets of background scenes, statistically representative of the diverse environmental conditions for a particular locale. Sample results are given of a Monte Carlo simulation of clouds over ocean at midlatitudes. In addition to graphic representations of the infrared radiance distributions, we outline the simulation methodology and the meteorological data base used for the statistical modeling of cloud cover. As an application we use this set of synthetic scenes to evaluate the performance of a drift-compensated temporal differencing algorithm for clutter suppression.

Cryogenic cooling techniques for spaceborne infrared detectors are surveyed, and reason found to explore alternatives. An alternative class of cooling cycles is defined, and four practical cycles described. A general overview of operating efficiency for the whole class is developed. One of these cycles, the isobaric absorption cycle (Servel cycle), is explored in some detail.

Novel low altitude infrared earth sensors are described. A static horizon sensor utilises the state of art technology in electronics to minimise the effect of radiance gradient by taking ratio of the radiometric signals by a hard wired or micro-processor based system. A scanning sensor is also being developed which scans radially at four edges on earth using a single scan assembly thus reducing errors caused by conventional techniques.

The status of current phenomenological models for high altitude plume signatures is presented. Major limitations are discussed and R&D efforts to remove these limitations are reviewed. These R&D projects are placed in two categories: fundamental properties and methodology development. Projects to obtain fundamental properties include: theoretical predictions/measurements of collisional excitation cross sections and vibrational relaxation rates, and measurements of physical/chemical properties of propellant aerosols. Methodology development include a composite high altitude signature model and an aerosol radiation model.

A detection range computation code which utilizes the Newton's recursive algorithm and the spectral convolution of the target and background emissions with atmospheric transmittance and detector sensitivity was developed and verified using near infrared laboratory measurements.

The molecules in the lower part of atmosphere are in thermal equilibrium with the local surrounding. The infrared emission resulted by their thermal excitation can be studied to determine their temperature and concentration profile in the atmosphere. We used a cryogenically cooled Fourier spectrometer mounted on a balloon-borne platform to study the infrared emission spectrum of atmosphere for this purpose. The experiment, which took place on October 7, 1981, at Holloman AFB, produced the analyzable data for more than two hours at altitude of 27000 ~ 28000 m along the horizontal and the vertical line of sight. The spectral data extended from 550 cm-1 to 1000 cm-1 covering the CO2 15μ bands (Δv2 = 1) with a resolution of 0.2 cm-1. The data were found interesting on two accounts: (1) a continuum background feature was superimposed with the molecular emission feature; (2) the radiance level of the CO2 15μ bands observed along the horizontal line of sight varied by a much greater degree than expected.

A simple model for developing band model parameters at moderate spectral resolution (~10 cm-1) is applied to the 6.3 μm H2O band. The underlying assumption of the approach is that the shapes of bands of the same symmetry can be superimposed to within ~10 cm-1. The band centers of the hot bands for H2O in the 6.3 μm are known, and the reference bandshapes can be generated from the AFGL HITRAN line atlas. A preliminary set of band model parameters is presented and compared to the NASA parameters.

A calculational comparison of a free molecular plume code (HAPAIR: High Altitude Plume-Atmosphere Interaction Radiation) and a Monte-Carlo Plume Code (TRAMP: Transitional and Rarefied Axisymmetric Monte-carlo Plume) is made for a selected sequence of cases going from a free molecular (Kn = 15) to a highl transitional (Kn = 0.07) flow regime. Results are presented which document the breakdown of free molecular flow assumptions in the transition regime and show the effect on the critical physical processes responsible for plume emission.