In recent years there have been rapid developments in the field of dynamic infrared scene projection, driven principally by the demands for real-time hardware-in-the-loop simulation and by the fortuitously concurrent advances in large array silicon surface micromachining techniques and addressing/multiplexing scheme electronics. A diversity of techniques have been explored towards satisfying the infrared projection requirements, resulting in a need for development of systematic comparative assessment procedures. In this paper the current status of infrared projector analysis is reviewed.

A 256 X 256 suspended resistor infrared scene generator system is being constructed. The system consists of a high technology core device which generates the infrared radiation and three conventional technology peripheral subsystems. At the time of writing, measurements have been made of the critical core device component parts, i.e., the transistor drive backplane and the suspended resistor superstructure separately, measurements of the complete integrated system have yet to be completed. Measurements of performance are presented and brief subsystem descriptions are included to aid in understanding of the overall system.

The scene generation test capability (SGTC) continues to be developed at Arnold Engineering Development Center (AEDC) using direct write scene generation. This test tool will be able to present realistic mission scenarios directly to sensor focal plane arrays for developmental and operational test and evaluation, and will be integrated with the full-up sensor test capabilities at AEDC. The concept validation phase of this program provided an operational system which is currently involved in sensor testing. Noise measurements have also been made in some detail on this system. The final phase of the program will provide scene projection at three infrared wavelengths and one visible wavelength. This paper presents an overview of the current SGTC program, including experimental data taken with the concept validation hardware.

Honeywell and MRC have been developing a range of thermal scene projector arrays through the Wright Laboratory Armament Directorate's cryovacuum resistive infrared scene projector (CRISP) program and the Defense Nuclear Agency's nuclear optical dynamic display system (NODDS) program. The resistive emitters are fabricated on silicon nitride structures on pitches as small as 2 mils. These structures have low thermal mass, low thermal conductance, and high fill factor. Monolithic address and pixel storage electronics provide flicker-free operation of large arrays at high frame rates. The emitters have demonstrated > 600 K blackbody temperatures, high radiance, and > 10³ dynamic range at very low power when operated at 40 K temperatures to achieve low background. This paper describes the performance of a CRISP 512 X 512 array consisting of 3.5 mil pixels and a high-speed 128 X 128 NODDS array consisting of ultra-low-power emitters.

Ever increasing developments in imaging infrared (IR) seekers that are being designed for Ballistic Missile Defense Office (BMDO) guided interceptor programs have amplified the necessity for robust hardware-in-the-loop (HWIL) testing to reduce program risk. Several candidate HWIL IR projection technologies are under development. This paper addresses the characterization measurements of a 128 X 128 metal-oxide semiconductor field-effect transistor (MOSFET) resistor array scene projector. The measurements include spectral output performance, dynamic range, spectral apparent temperature, uniformity, rise time, fall time, droop percentage, and current consumption. With possibly the exception of hot target simulation, the resistor array has the ability to spatially, spectrally, and temporarily function as the scene projector for a HWIL facility.

As was previously reported, a spatial light modulator (SLM) is being fabricated that exploits vanadium dioxide's (VO₂) thermally induced transition from a semiconductive-to-metallic state. This transformation causes the film to change from a state of low to high reflectivity in the 3 - 12 micrometers region. Thermal control of the VO₂ is provided by an array of p-n junction diodes, each diode constituting the center of a single `pixel' in the SLM. As power is applied to a diode, it generates heat, thereby providing an electrical means of controlling the reflective state of the VO₂ film on its surface. The design of the SLM is driven by the need for a high optical contrast, large scale implementation, and high refresh rate. Unfortunately, these requirements are not conducive to each other, so compromises must be made. Optimizations of this design using either microchannel or chemical vapor deposition diamond heat sinks are reported. Both of these simulated designs attained pixel switching times in excess of 650 Hz.

This paper describes the initial development of an IR scene projection system that will produce time-varying scenes using the Texas Instruments digital mirror device (DMD). We develop a dark field IR projector design in which light reflected from a DMD pixel is reflected into the aperture of the projector when the pixel is on and remains outside the aperture when the pixel is off. We apply an effective blackbody temperature model and a previously developed diffraction model to a projector design with an aperture stop smaller than the main lobe of the on pixel diffracted light. We show that this arrangement provides optimum blackbody temperature and image resolution performance. We calculate that a projector of this type could produce adequate resolution with effective temperatures of almost 400 degree(s)C. A breadboard DMD scene projector using a filtered quartz tungsten-halogen light source which provided IR emission at 1 micrometers and a 768 X 576 digital DMD device with 16 micrometers pixels was constructed. A contrast ratio of over 100 to 1 was observed with resolutions greater than one-half of the device resolution. A preliminary optical illumination and projection design is described for a brassboard DMD IR scene projector.

This paper reviews the principles of operation of the electron- beam-addressed membrane-mirror-light-valve-based IR scene projector, and reports on recent advances in it s development for the 3- to 5-micrometers waveband. In particular, recently built projectors with 128 X 128 pixels have exhibited 30-Hz flickerless operation, contrast rations in excess of 100:1 when read out with blackbody sources, and up to 75% readout optical efficiency. A compact high-efficiency readout optical system for coupling the output image into cameras and test systems was also explored.

The speed demands that determine the frame rate requirements for dynamic infrared scene projectors are discussed together with the speed characteristics and limitations of the scene projectors currently being developed. Multiplexing/addressing scheme limitations are discussed and specific infrared projection technologies are surveyed with particular attention given to the design compromises that tend to determine speed capability.

A model is proposed for determining the effect of image clutter on the time-line behavior of observer eye fixations when searching for targets in infrared scenery. Several possible metrics for qualitatively evaluating the degree of clutter are tested. Correlations between these metrics, the probability of fixating a particular area, and the length of time spent fixating a particular area are discussed.

This paper describes the development of a new version of the SHARC code, SHARC-3, which includes the ability to simulate changing atmospheric conditions along the line-of-sight (LOS) paths being calculated. SHARC has been developed by the U.S. Air Force for the rapid and accurate calculation of upper atmospheric IR radiance and transmittance spectra with a resolution of better than 1 cm^-1 in the 2 to 40 micrometers (250 to 5,000 cm^-1) wavelength region for arbitrary LOSs in the 50 - 300 km altitude regime. SHARC accounts for the production, loss, and energy transfer processes among the molecular vibrational states important to this spectral region. Auroral production and excitation of CO₂, NO, and NO⁺ are included in addition to quiescent atmospheric processes. Calculated vibrational temperatures are found to be similar to results from other non-LTE codes, and SHARC's equivalent-width spectral algorithm provides very good agreement with much more time-consuming `exact' line-by-line methods. Calculations and data comparisons illustrating the features of SHARC-3 are presented.

There has been much interest in scene correlation length as a tool for characterizing backgrounds. However, since a camera acts as a band-pass filter for spatial frequencies, with the high frequency cutoff determined by the resolution and the low frequency cutoff being determined by the field of view estimates of scene correlation length that have been calculated from digital images must be interpreted in terms of the pass-band of the camera used. The investigator must consider whether the pass band of the camera has significantly affected the spatial frequency spectrum and, as a result, the measured correlation length. In addition to filtering, the spatial frequency spectrum and the measured correlation length may be affected by aliasing. In general, high-pass filtering results in a reduction in the apparent correlation length while aliasing and low-pass filtering result in an increase in the apparent correlation length. Varying the position of the camera provides a means of detecting both filtering and aliasing, and the authors suggest criteria for determining whether these effects have significantly affected the spatial frequency spectrum and the resulting correlation length.

The Midcourse Space Experiment Satellite (MSX) has a suite of ultraviolet and visible imaging spectrographs and imagers that cover the wavelength range from 110 to 900 nm. The versatile pointing capability of the satellite allows observations in the earth limb and below the horizon with observations during the day and night. The wavelength resolution (1 - 3 nm) for the spectrographs and high spatial resolution in the filtered imagers allows experiments covering a multitude of background phenomenology issues. Experiments are designed to look at ultraviolet through the visible clutter issues for many different scene conditions in the earth limb and below the horizon. Hyperspectral images of terrain and ocean features for specific locations are in the planning stages specially at specific ground truth locations. Atmospheric emission sources during the day and night in different global locations. Atmospheric emission sources during the day and night in different global locations from the poles to the equator will be observed for both assessment of radiance and clutter issues as well as for input into atmospheric radiance models.

This paper addresses the feasibility and operational application of different infrared (IR) imaging systems in road traffic to improve security of individual motor vehicles at conditions of low visibility, especially in fog. Extensive field measurements were carried out at different weather conditions, mainly fog and haze, utilizing three IR imaging sensors in different spectral bands in the near and thermal infrared. Additionally, a CCD camera in the visible band was used for comparison purposes. Measurements were performed on public roads and a test road which was equipped with heated and unheated radiation reference sources and thermal beacons. Furthermore, the atmospheric spectral transmission and relevant meteorological and aerosol parameters were measured. A mathematical model, SIMIS (simulation model for IR scenes), was developed and applied to generate and analyze thermal images of the test road. The spectral dependencies and radiation properties of fog and haze were modelled with LOWTRAN 7. Apparent radiances, temperatures, and contrasts of the references sources were simulated as a function of distance. The contrast transmission and effective IR visibility was derived and compared to the measured IR-imaging sensor data. From the analysis an assessment of the performance of IR-imaging sensors at fog conditions has been deduced.

The TECOM Ft Belvoir Meteorological Team and the Night Vision and Electronic Sensor Directorate of CECOM contracted with EOIR to develop a new instrument which would provide atmospheric transmissivity data in the 35 gigahertz region. The desired instrument would have complete redundancy, long path length, compact size, stable microwave performance, easy field setup and alignment, standard data output, low development risk, and, above all, low system cost. The design by EOIR consists of mostly off-the-shelf components with a design goal of measuring 1% transmission over a 5 km path which corresponds to a rainfall rate of over 64 millimeters per hour. To achieve simplicity of design and field use and to keep cost down, two innovations have been made. First, a new antenna design that uses optical refraction principles replaces the large and cumbersome parabolic antennas and second, an open loop frequency design, as opposed to a frequency tracking receiver, allows for the use of less expensive transmitters and receivers. In this paper we describe the instrument and present some initial performance data.

The features of forming a signal-to-noise ratio (SNR) as applied to the pulse-coded information transfer technique through an optical channel are considered. To maximize a SNR and a range of communication, an optimum receiver resolution time (RRT) should be found and used. An analytical solution as well as an algorithm to calculate the distortion of a pulse, propagating through a cloud layer, and the position and amplitude of a maximum of a recorded signal have been developed. They were realized as an interactive PC program, which calculates the optimum value of RRT and range limit of communication for any parameters of systems and optical channels (atmosphere + cloud).

The temporal coherence function of light field in a medium with Brownian-moving scatterers is considered. Both translation and rotation of scatterers is taken into account. Relying upon this base, time-averaged holographic imaging of a rough-surface object through a medium with moving scatterers is considered. Transfer characteristics (optical and modulation transfer functions, coefficient of backscattering noise transfer) and contrast in an object image as a function of hologram recording time are investigated.

We consider a model 3D stationary problem of wave propagation in a fluctuating weakly dissipative layered halfspace. The statistical analysis of this problem is carried out in the framework of the imbedding method for different boundary conditions. We are interested in the statistical behavior of the averaged intensity, which is expressed via a two-frequency correlator of waves incident at different angles. The correlator is calculated both analytically in the framework of the diffusive approximation and numerically with the help of the statistical simulation method.

Correlation functions give a lot of information for the description of wavefields and for characters of media. We study the influence of correlations on the form of statistics of the model under consideration. The main points of such influence are the relations between correlations and the number of degrees of freedom of the model. The presence of correlations means certain reducing of full number of degrees of freedom, the absence of any correlations means that the system is realized over max value of degrees of freedom. That statement permits us to take into account the possible significance of phase space dimension (PSD) D of the system (the number of degrees of freedom of the system) on the form of partition function. The presence of correlations leads to the reducing of PSD D, and hence D might be treated as one of the fluctuating parameters in the procedure of deriving Gibbs partition function. Thus we present the partition function, that describes probability of realization for different values of PSD D and hence gives certain descriptions of the correlated behavior of our system. Simple cases and relations with the problems of wave propagation in random media are discussed.

We consider the problem of the oblique incidence of a wave on the half-space of layered randomly inhomogeneous medium without absorption and analyze the influence of boundary conditions on probability distribution of the reflection coefficient phase and statistical behavior of the wavefield intensity moments inside the medium.

Solution of practical problems of remote sensing in homogeneous atmosphere is based on the connection among parameters of sources and atmosphere inhomogeneities and spatial-temporal structures of the received signals. In this investigation we represent the effective technique: transferal coefficients (TC) for the solution of the problems of source and inhomogeneity probing in the refractive waveguides. We propose using the coefficient of energetic coupling and the anisotropy coefficient and mean time reaching, dispersion of the reaching time, and probability of differentiation of direct and scattered signals. The properties of the TC are determined only by the properties of temperature and sound velocity distribution in waveguides. The application of TC of inhomogeneous refractive atmosphere gives us the possibility to construct a priori spatial-temporal structure of background in the case of remote sensing of sources and to investigate the form of observation region and some of the spectral characteristics when we want to probe the inhomogeneities. We represent the calculated spatial maps of TC for the different types of waveguides. The possibilities of the calculation of these maps for the waveguide with localized inhomogeneities and the problems of optimization of receiving systems are discussed.

Two Midcourse Space Experiment (MSX) experiments are designed to obtain data on terrestrial (below the horizon) and low earthlimb (low above the horizon, below 40 km tangent height) backgrounds as seen from the MSX satellite by the SPIRIT III cryogenically cooled radiometer and UVISI imagers. The radiometer will provide data in two mid-wave infrared bands with a spatial resolution of 90 (mu) radians and a temporal resolution of at least 13.9 msec to characterize the small scale structure of the backgrounds and their global distribution. Other instruments aboard the MSX payload will provide supporting spectral and spatial imagery data for correlating phenomenological behavior in the ultraviolet, visible, and infrared regions of the spectrum. The 18-month duration of the cryogen will afford many opportunities to sample the backgrounds during all seasons, cloud and terrain conditions, day, night, and terminator scenes, and a variety of solar scattering angles. Automated data processing will provide rapid reduction of the data and generate products characterizing the scene content and statistical distribution of radiance as well as indices for cataloging the data.

A major objective of the MSX program is to obtain global data of atmospheric and terrestrial backgrounds simultaneously in the infrared (2.6 to 28 micrometers ) and short wave (0.11 to 0.9 micrometers ) spectral regions. This paper presents an overview of the plans and capabilities to measure infrared earthlimb and terrestrial backgrounds with the cryogenic infrared MSX sensor, the spatial Infrared Imaging Telescope (SPIRIT) III sensor. Of particular importance is the characterization of the spatial-temporal structure and the global distribution of mean radiometric levels and spectral content of both quiescent atmospheric and terrestrial backgrounds as well as the backgrounds associated with aurora, mesospheric and noctilucent clouds, stratospheric warmings, wave phenomena, scatter and thermal emissions from clouds, terrain, and other sources. Experiments are planned to collect data as a function of latitude, season, diurnal conditions, magnetic activity and altitude, up to tangent heights of 300 km over a period of 18 months for the infrared (cryogen lifetime) and 5 years for the visible and ultraviolet sensors. Coordinated experiments are planned with ground sites and in conjunction with other satellites. Automated processing will provide rapid data reduction and the generation of data products.

Simulation of infrared radiance fluctuations in the atmosphere depends on detailed descriptions of fluctuations in atmospheric species number densities, vibrational state populations, and the kinetic temperatures along the sensor line-of-sight. The relationship between kinetic and vibrational temperature fluctuations depends on the subtle interplay between changes in the total number densities, changes in the temperature-dependent kinetic rates, and the relative contribution of the radiative relaxation. The model developed in this paper predicts the two- dimensional radiance covariance function for nonequilibrium effect conditions. The radiance statistics are non-stationary and are explicitly bandpass and sensor FOV dependent. The SHARC model is used to calculate mean LOS radiance values and radiance derivatives which are necessary to determine the radiance statistics. Inputs to the model include the statistical parameters of a non-stationary atmospheric temperature fluctuation model and an atmospheric profile. The radiance statistics are used in a simple model for synthesizing images. The model has been applied to calculate the radiance structure for the OH((Delta) v equals 1) SWIR band and the CO₂((nu) ₃) MWIR band under nighttime conditions.

The European Union and DLR are funding a new 79-channel airborne imaging spectrometer: DAIS-7915, which is built by GER Corporation. Based on the requirements for ground calibration of the DAIS-7915, a Universal Calibration Facility (UCF) for VIS-TIR wide-angel videospectrometric airborne sensors has been developed at the DLR-Institute of Optoelectronic. The spectral coverage of the UCF is 0.4 - 14.5 micrometers . The UCF consists of the spectrometric-geometric calibration part (SCP), the relative diffuse radiometric source (RDRS), the thermal absolute calibration part (TACP) and the absolute radiometric calibration part (ARCP). The SCP, RDRS, and TACP can be used for laboratory calibration as well as for hangar calibration of the sensor installed in the aircraft. The ARCP consists of an integrating sphere with 165 cm diameter and an opening of 40 X 55 cm². The sphere is intercalibrated by means of an absolute diffuse source (ADS) and a spectro- radiometer. The ADS has been recognized and admitted for application as a reference instrument for measuring the spectral radiance in the wavelength region of 0.4 - 2.5 micrometers .

In previous papers we have presented measurements of degree of polarization in the mid and far infrared both in near-horizon sun-glint and in the adjacent sea background radiance. The polarization has been related to the Fresnel reflection and emission coefficients and compared with predictions. These measurements have been extended to include target-to-background polarization contrast measurements. Target polarization was small, but sea surface emission showed moderate degree of polarization in the p-plane (vertical). Considerable ship- background contrast improvement was achieved by polarization filtering in the horizontal plane. This effect was greater in the far infrared. Values are given for the degree of polarization of target and background and the contrast improvement factor due to polarization filtering.

A program system for displaying and analyzing IR-background-images is presented. This system allows analysis of image data -- statistical and textural parameters of the entire scenery or of a predefined image section -- for a specified scenery image series. Subsequently, statistical relationships like correlations between image parameters on the one hand, and meteorological parameters as well as time of day and season on the other hand, are evaluated. Results will predominantly be used for the development and validation of tactical decision aids for IR-range forecasts. In addition, evaluations might be of interest for performance assessment of camouflage and EO-systems efficiency. Actually, the program system is being applied to the evaluation of two data sets, each of them comprising measurements (infra-red images with synchronous weather data) over one year. One data set was obtained in norther Germany, the other one in southern Germany. The data base contains a total of about 12,000 IR-images, for a variety of specified sceneries, seasons, and weather situations. Some preliminary results are shown and discussed.

In the electro-optical target detection community, there is considerable interest in finding quantitative measures of detection performance, such as the (Delta) (Tau) metric of contrast between a target and background. As a measure of target detectability against a variety of backgrounds, this paper discusses a new, generalized signal-to-clutter ratio (SCR), which has many attractive features, such as detailed quantification of the role of target shape, clutter spatial statistics, and interchannel correlation (including color) on detectability. Using this measure of performance, it is easy to produce plots showing detection probability in terms of false alarm rate using a standard probability curve. To provide insight, some intuitive examples are presented of the role played by spatial/frequency matrix blocks in the generalized SCR. Finally, it is shown that when certain approximations or simplifications are made, the generalized signal-to-clutter metric discussed here does specialize to other, simpler and more familiar measures of detectability.

EO/IR/FLIR sensor performance models currently employ a thermal difference metric(s) to predict target detection, recognition, and identification ranges in conjunction with minimum resolvable temperature difference (MRT) curves. In this paper, we present a target, atmosphere, background, and sensor-specific (TABSS) thermal difference metric, minimizing shortcomings and deficiencies of other thermal difference metrics currently used in thermal imaging system performance models. This metric is parametrically compared with other (Delta) (Tau) metrics. We also investigate target, background, and scene pixel variances behavior as the scene maps to a fewer number of pixels, which reveals potential applications in clutter metrics as well as detection, recognition, and identification range predictions. Finally, we survey current status of sensor performance models to seek an application of the TABSS (Delta) (Tau) metrics. We find that this metric will enhance the current thermal imaging system performance models to accurately predict detection, recognition, and identification ranges not only when the thermal difference is large, but especially when the thermal difference is small.

Texture is an important preattentive cue in region-based segmentation of images. In this paper, we provide an objective comparison of the properties of the Gabor functions and the circular- Mellin features for texture segmentation. The Gabor functions provide a spectral decomposition of a windowed image about a unique spatial frequency in the Cartesian coordinate system. The circular-Mellin operators represent the spectral decomposition of the image scene in the polar-log coordinate system and are invariant to both scale and orientation of the target. Coupled with the unique shift invariance property of the correlator architecture, these circular-Mellin operators can be used for rotation- and scale-invariant feature extraction. We note that while both these feature extractors have similar functional form, the distortion- invariant characteristics of the circular-Mellin operators make them preferable for texture segmentation. Segmentation results to demonstrate their salient properties are presented.

Image texture plays a vital role in the segmentation process. A novel unsupervised segmentation approach based on multiresolution cooperative texture model computation is developed. The multiresolution segmentation approach is based on the observation that the human visual system utilizes relatively `global' information about an image in conjunction with `local' information to reach segmentation decisions. The texture model developed is based on sets of gray level co-occurrence matrices rather than measures extracted from them. The concept of multiresolution associated region (MAR) is developed for pyramid schemes. The other algorithmic constituents for the segmentation scheme such as normalized match distances between texture models, region homogeneity criteria with extensions to MARs, are systematically developed. The MAR aggregation rule is utilized to perform segmentation decisions at the base resolution level. The segmentation strategy was tested extensively on natural texture mosaics as well as on real scenes and the results are analytically presented. An important observation was that smaller texture models at multiple resolutions performed better than a very large texture model at single resolution.

The current status of U.S. efforts in infrared background and model development is assessed. The paper includes discussions with both DoD and contractor research personnel active in data collection, system design, and background modeling, backed up by examination of a large body of existing reports and data. Future background measurement programs as well as the directions that background modeling efforts are taking are also discussed.

The methods currently used for the generation of wind roughened sea surfaces suffer shortcomings. This paper shows that in the one-dimensional case (i.e. looking at the vertical movements of a single point on a sea surface in time) the problem of generating a time series of surface heights having the correct autocorrelation function and the required Cox-Munk distribution of slopes can be solved by generating a Gaussian random sequence with the appropriate autocorrelation function, and passing it through a non-linear pointwise transform to generate a sequence with the required properties. In the two-dimensional case the problem is not yet completely solved, as it is not clear whether an appropriate field of slopes can be integrated to generate a field of wave heights. Nevertheless, the results obtained so far serve as a correction to the algorithm where a pseudo sea surface is generated by convolving a field of independent slope values drawn from a Cox-Munk distribution with a spatial filter derived from the Pierson-Moskowitz power spectral density of surface heights.

Fractal geometry provides the ideal paradigm for simulating and modeling natural terrain. Many outstanding examples of fractal terrain are found in the open literature. There is, however, an unfortunate false impression that such landscapes are difficult or complicated to create. Although the `rendering' process may be complex, the actual generation of fractal landscapes or the addition of fractal texture to existing elevation profiles is quite simple. This paper presents the code necessary to generate a detailed fractal landscape using MathCad^TM ver. 5.0+ and the Signal Processing Function Pack. The resulting data array may be rendered for even higher realism by the investigator. In this case, a commercial- off-the-shelf package for the IBM PC called Vistapro Ver. 3.0 is used to render the synthetic landscape in even higher detail.

This paper describes a new image generation software code for creating radiometrically accurate images in the visible and near-infrared wavelength band. It was developed to evaluate pilot vision through aircraft windscreens and was written to operate in conjunction with an off- the-shelf computer animation software package. This capability allows the user to take advantage of the geometric modeling and motion generation capabilities inherent within the computer animation software for scene and scenario generation while using the new image generation codes for sensor modeling. The code, called TAV-IR, uses spectral reflectance and transmittance data as a function of incidence angle to describe surface material properties and spectral illumination data to model light sources. Once the operator selects the wavelength band of interest, the spectral sampling rate and the image size, the code produces an `image cube' consisting of floating point radiometric values for each pixel and each wavelength bin modeled. This image cube is then post-processed for sensor modeling purposes and image display. The code also reads an output file from a thin-film optical coating analysis package so that the reflective and transmissive properties of coated windscreens can be modeled. An interactive image inspection and display tool with a graphical user interface was also developed. This interactive tool, called SPEC, allows image pan and zoom and permits the operator to select pixels in the scene and view the spectral data contained in the selected pixels.

Visibility and visual range are well established concepts that quantify the exponential attenuation of contrast and radiance along near-horizontal paths through the atmosphere. Scene visualization, however, requires that not only the attenuation of radiance from distant objects be modeled, but also the scattering of ambient radiance into the field of view all along the viewing path. This illumination effect is most pronounced under moderate to low visibility conditions of haze or fog viewed from near-horizontal paths near the surface. It is often provided for in scene generators that implement some form of range-dependent `fog' or `haze' functions as two parameters: the `atmospheric fading coefficient' and the `atmospheric blending factor.' We examine the physical meaning of these parameters and the effects of variable illumination and terrain reflectance along the viewing path for different meteorological visibility, solar angle and aerosol conditions. The error introduced through use of the same coefficients across the visible wavelength band is compared to use of wavelength- dependent extinction and scattering. Scene generation examples are shown comparing different rendering approaches and the trade-offs in computational speed versus accuracy between hardware and software implementations.

The 3D volumetric character of clouds is a critically important factor in determining cloud structure as seen in infrared imagery. Using a longwave cloud scene simulator which images a 3D cloud volume, the 3D structure has been shown to be particularly important when viewing at low grazing angles. In order to conduct analyses of cloud scene structure in MW and visible bands as well, the longwave simulator has been significantly upgraded to perform imaging of clouds with multiple scattering included. The multiple scattering algorithm is based on a WKB approximation method for the exact radiative transfer problem, and comprehends the spatial variations in optical properties within the cloud volume. As a first analysis, we have generated a cloud scene which is backlit by the sun, and systematically assess the contributions of the thermal, solar, and multiple scattering mechanisms within the imagery. As might be expected, multiple scattering has its greatest impact at the cloud edges in the MW band, where the `silver lining' is formed.

The digital imaging and remote sensing laboratory's image generation model (DIRSIG) was validated in the long wave infrared (LWIR, 8 - 13.3 micrometers ) and midwife infrared (MWIR, 3 - 5 micrometers ) pass bands. Truth data was collected for all components of the thermal and radiometric submodels including a complete set of meteorological and radiometric data. Truth temperatures were collected using a bank of thermistors and truth radiance images were collected with calibrated InSb (MWIR) and HgCdTe (LWIR) detectors. Sensor spectral response functions were also included in the radiometric analysis. Relative error contributions to the total temperature/radiance digital count were investigated for each component in the multi-spectral model. Largest contributions were found to be wind speed, air temperature, visible emissivity, and fractional sky exposure for the thermal model and atmospheric transmission, temperature, and emissivity for the radiance model. An overall comparison of truth and synthetic images yields rms errors of as low as 1.8 degree(s)C actual temperature and 5 degree(s)C (LWIR) and 6 degree(s)C (MWIR) apparent temperature.

A new theoretical approach based on stochastic nonequilibrium thermodynamics has been proposed to describe an evolution of plants. Thermodynamic characteristics of plants and analytical expressions for the effects of ecological stress factors are found.

The focus of the current research is to numerically predict an infrared image of a jet engine exhaust plume, given field variables such as temperature, pressure, and exhaust plume constituents as a function of spatial position within the plume, and to compare this predicted image directly with measured data. This work is motivated by the need to validate CFD codes through infrared imaging. The technique of reducing the 3D field-variable domain to a 2D infrared image invokes the use of an inverse Monte-Carlo ray trace algorithm and an infrared band model for exhaust gases. This paper describes an experiment in which the above- mentioned field variables were carefully measured. Data from this experiment in the form of velocity plots are shown. The inverse Monte-Carlo ray trace technique is described. Finally, an experimentally obtained infrared image is directly compared to an infrared image predicted from the measured field variables.

Given the task of modifying color images for atmospheric effects one step involves recasting the color (red, green, blue) pixel information as spectrally resolved information that can be modified for transmission, path radiance, and aerosol-forward-scatter/turbulence blurring effects. The paper describes the means of using sensor spectral response functions to perform the spectral estimation task. Spectral data is recorded as a function of pixel position and waveband using a series of object-oriented C++ classes. Each waveband image is processed separately for atmospheric effects, and the output spectral images are used to create an output color image. The estimation technique begins by defining a color space that is the analog of human chromaticity space. Sensor spectral responsivity data is required as input and used in providing a series of monoband response points and three templates related to the red, green, and blue response functions. The estimation technique involves direct calculations for color coordinates within the red/green/blue triangle. For valid color coordinates outside this triangle, an iterative technique was developed.

A model for prediction of minimum resolvable contrast (MRC) as applied to TV sensors, and an MRC measuring instrument, have been developed. Several equations exist for calculation of MRC, deriving from the work of Rosell on vidicon based sensors, and these form the basis of our model. Recent workers touch on the MTF of CCD sensors, and such work, together with a derivation of noise equivalent contrast, has been applied to extend the applicability of our model to these types of sensor. A means of directly evaluating the MRC concept was also desired, both to validate the model, and to measure the performance of individual sensors. A compact MRC measuring instrument was therefore built, and details of its construction and use are presented.

SHIPIR is a model which simulates infrared images of ships at sea. The model is divided in five main modules. The ship model definition module defines the ship geometry, the thermal plates, the radiative surfaces, and the user-specified thermal boundary conditions. The simulation condition definition module gathers all necessary inputs to simulate a specific IR image. The background irradiance computation module runs Lowtran7 to compute atmospheric transmittance and radiance, direct solar irradiance and sea irradiance on the ship and the observer. The heat transfer solution is then computed with a steady-state algorithm, generating the ship surface temperatures. The infrared scene generation module creates the scene as viewed by an observer in a predefined waveband and at a position that can be changed interactively. A simple IR plume image is also generated at this stage. This paper describes the different modules that are part of the model. Examples of the outputs generated with a baseline scenario are given. The steps and results of a validation experiment performed with data from two instrumented plates are highlighted.

Current efforts to design reliable background scene generation programs require validation using real images for comparison. A crucial step in making objective comparisons is to parameterize the real and generated images into a common set of feature metrics. Such metrics can be derived from statistical and transform-based analyses and yield information about the structures and textures present in various image regions of interest. This paper presents the results of such a metrics-development process for the smart weapons operability enhancement (SWOE) joint test and evaluation (JT&E) program. Statistical and transform based techniques were applied to images obtained from two separate locations, Grayling, Michigan and Yuma, Arizona, at various times of day and under a variety of environmental conditions. Statistical analyses of scene radiance distributions and `clutter' content were performed both spatially and temporally. Fourier and wavelet transform methods were applied as well. Results and their interpretations are given for the image analyses. The metrics that provide the clearest and most reliable distinction between feature classes are recommended.

In the analysis of scene content of an infrared (IR) imager the optical transfer function (OTF) must be determined. For broadband systems the OTF is dependent upon the optics detector response and source spectral characteristics. For an IR imaging system with a 15.24 cm diameter Cassegrain telescope and 5.08 cm diameter central obscuration, the OTF can readily be approximated for monochromatic scene radiation. The spectral conditions of interest are those of a hot blackbody (BB) source to that of one at ambient temperature. The differing system conditions of interest are those of a filtered IR detector versus an unfiltered detector for the 8 - 12 micrometers spectral region. The environmental conditions of interest are those of dry versus humid atmospheres. For humid atmospheres the filtered detector has a distinct sensitivity advantage in that it can block out undesired path radiance from atmospheric constituents that would decrease the signal to noise ratio. For a dry atmosphere the unfiltered detector would have an advantage in that it would have a wider spectral response and receive more of the emitted source radiation yielding better spatial resolution near high frequency cutoff.

The advent of missile seekers with dual-mode millimeter wave and infrared common-aperture sensors has led to a requirement to develop the simulation tools necessary to test these systems. Traditionally, one of the most important techniques for supporting systems development has been a full seeker hardware-in-the-loop simulation. Over the past twenty years, there has been a substantial effort to develop the required simulators for supporting development of systems that utilize single-mode guidance. However, the development of comparable simulation facilities capable of supporting the new generation of advanced dual- mode guided systems has been limited due to some major technological challenges that are not readily overcome. This paper provides an overview of the simulation facilities available at the U.S. Army Missile Command to support systems development of single-mode and non- common-aperture dual-mode systems, presents the major technological challenges that limit common-aperture dual-mode simulator development, and provides a conceptual description of a dual-mode simulator capable of providing simultaneous imagery to both sensors of a common-aperture seeker.

This paper provides an overview of the HWIL simulations of IR systems, addresses the critical projector requirements/specifications for HWIL simulations, and reviews the most prominent technologies associated with IR scene projection. This review consists of a brief discussion of each technology in terms of physical operation with advantages and disadvantages being highlighted. Following this introduction, the IR target-slide zoom-optics projector (IRTZP) and IR laser diode array projector (LDAP) systems which are currently developed by MICOM are thoroughly discussed. This includes a discussion of the operational performance characteristics of both systems. The basis for this paper is work performed at the MICOM Advanced Simulation Center (ASC). The ASC is managed and operated by the Systems Simulation and Development Directorate of the MICOM Research, Development, and Engineering Center, Redstone Arsenal, Alabama.