Liquid crystal writable grating technology is being developed for beam steering in laser radar systems. To date, steering of 10.6 micrometers , 1.06 micrometers , and 0.53 micrometers wavelengths has been demonstrated. Preliminary results are described. In this paper we also consider the ability of writable gratings to steer broad spectral band radiation for use in passive sensors. We find that there is potential for these devices in microscan systems because there is little or no dispersion for the small scan angles required in microscanning. The dispersion that is present is less than the resolution of the sensor considered here. For large angle steering we find that dispersion correction or a narrowing of the spectral bandwidth is required. Approaches for dispersion correction and post-detection compensation are discussed.

With the increasing availability and applicability of staring focal plane array (FPA) thermal imagers, the accurate modeling of these sensors is a critical requirement within the infrared community. The FLIR92 sensor performance model, developed by the U.S. Army Night Vision and Electronic Sensors Directorate (NVESD), provides the capability to predict laboratory performance for staring FPA thermal imagers. FLIR92 uses readily available system level parameters to predict the device MRTD and MDTD. This paper illustrates the techniques used in the model by evaluating performance for a staring FPA thermal imager.

For several years the Night Vision and Electronic Sensors Directorate (NVESD) has been using an internally developed forward looking infrared (FLIR) simulation program. In response to interest in the simulation part of these projects by other organizations, NVESD has been working on a new version of the simulation, NVSIM, that will be made generally available to the FLIR using community. NVSIM uses basic FLIR specification data, high resolution thermal input imagery and spatial domain image processing techniques to produce simulated image outputs from a broad variety of FLIRs. It is being built around modular programming techniques to allow simpler addition of more sensor effects. The modularity also allows selective inclusion and exclusion of individual sensor effects at run time. The simulation has been written in the industry standard ANSI C programming language under the widely used UNIX operating system to make it easily portable to a wide variety of computer platforms.

Often electro-optical (EO) imaging systems in the thermal infrared (IR) are used for applications for which they were not originally designed. On the flip side, EO imaging systems are touted as applicable for scenarios when the magnitude of the effects of the environment (that can and do occur) have not been adequately characterized. As a result when an imaging system does not perform as expected, there is much pointing of fingers to place blame and discussion of environmental bugs (counterpart to computer bugs) getting into the equipment and fouling up the works. Some examples of these subtle problems that impact the design and use of EO imaging systems in the thermal IR are discussed in this paper, particularly the effects of optical turbulence, path radiance, and field calibration.

Natural scenes are not band-limited and for most contemporary sampled imaging systems, the (pre-sampling) image formation subsystem frequency response extends well beyond the sampling passband. For these two reasons, most sampled imaging systems -- particularly staring-array systems -- produce aliasing. That is, the sampling process causes (high) spatial frequencies beyond the sampling passband to fold into (lower) spatial frequencies within the sampling passband. When the aliased, sampled image data is then reconstructed, usually by image display, potentially significant image degradation can be produced. This is a well- established theoretical result which can be (and has been, by many) verified experimentally. In this paper we argue that, for the purposes of system design and digital image processing, aliasing should be treated as signal-dependent, additive noise. The argument is both theoretical and experimental. That is, we present a model-based justification for this argument. We demonstrate that our model-based argument leads naturally to system design metrics which quantify the extent of aliasing. And, by illustrating several `aliased component' images, we provide a qualitative assessment of aliasing as noise.

Noise must always be considered in predicting the performance of a thermal imaging system. The optimum sensitivity of such a system is achieved when the system is `background noise limited' -- that is, when the predominant source of noise is that associated with the random arrival of photons onto the infrared detector. In the absence of other noise sources, the fluctuation in the detector output has a white noise spectrum which is then modified by sampling, filtering, digitizing, or whatever other signal processing is applied. When other significant noise sources exist, their effect on the output noise spectrum must be properly analyzed if sensor performance is to be adequately estimated. This paper discusses several excess noise sources and explains how to combine these sources with background noise. The principal emphasis is on scanning sensors using second-generation detector arrays, commonly referred to as `focal plane arrays.' Excess noise sources considered include 1/f noise, digitization noise and several types of fixed pattern noise as well as white noise associated with signal amplification. The effects of the resultant total noise spectrum on both NETD and MRTD are analyzed.

The alternative approach presented in a previous conference paper in which spatially dependent expressions were derived for infrared signal and displayed signal-to-noise ratio is extended to reveal the sources of infrared contrast at each pixel site and to the consequent development of methods by which signal and displayed SNR can be calculated across a thermal image.

Recent work by BDM for U.S. Army Missile Command (MICOM) indicates that current MRTD-based infrared sensor performance models (e.g., FLIR90/ACQUIRE, MIISPM) may not adequately model the effect of low frequency system noise on predicted system field performance. This paper addresses a computer modeling exercise conducted by BDM using the MRTD-based MIISPM in conjunction with the 3-D noise model developed by D'Agostino, et al., at the US Army NVESD to predict the effect of modifying a low frequency noise specification on the field performance of a hypothetical imaging IR target acquisition sensor that utilizes a second generation infrared focal plane array (IRFPA). Contrary to intuition, computer modeling results indicate that large increases or decreases in the low frequency system noise have little impact on predicted field performance.

EO_VISION was developed as a companion to analytical sensor models in that it provides real-time visualization of sensor processed target imbedded scenes for comparison to modeled range performance. Sensor processed scene effects are generated based upon FLIR92 sensor characterizations and ACQUIRE's environmental effects. Processed scenes containing sensor resolution sampling and noise degradation effects are generated and projected in real-time for viewing at sensor frame/field rates to determine the validity of target acquisition range performance predicted by the analytical models. The paper describes the techniques implemented with EO_VISION to simulate sensor effects to include resolution loss, filtered 1/f and broadband noise, raster forming and down-sampling. Methodology used to generate input imagery is described and representative input versus sensor processed scene prints provided. Finally, the application of EO-VISION to other tasks such as realistic perception experiments, target acquisition training, search experiments, ATR testing and imagery database management is discussed.

This paper describes the Illowra forward looking infrared (FLIR) performance model, which has been developed by the Defence Science and Technology Organisation (DSTO) and British Aerospace Australia (BAeA). The Illowra model enables calculations of system performance to be carried out for a wide range of FLIR technologies including thermal, photoconductive, and photovoltaic detector based systems used in various staring and scanning detector geometries. Illowra can produce images of target/background scenes, showing spatial and noise effects introduced by a FLIR system. The performance of the human observer, in terms of target detection, recognition, and identification probability, is calculated using the Oracle visual performance model developed by British Aerospace, UK. An outline of the structure and operation of the model is given, followed by a description of how Illowra has been used for various applications within DSTO. The paper concludes with a description of some of the most recent enhancements to Illowra.

This paper presents an analytical method to effectively and rapidly evaluate the impact of airframe suppression on electro-optical/infrared (E-O/IR) system lock-on range. This method is known as the Effective Rapid Airframe Suppression Evaluation (ERASE). It can be used to perform tradeoff analyses with respect to IR suppression systems and evaluate the impact of these systems on E-O/IR systems. This paper discusses a new set of dimensionless equations and how these equations are used to evaluate changes in airframe area, temperature, emissivity, and reflectivity (as a function of earthshine, solar reflections, and skyshine). Since the ERASE code has been formulated as a rapid computational tool (capable of generating over 1000 design variations in minutes), it is ideal for performing design tradeoffs against airframe shaping, thermal control systems, and diffuse reflectivity/emissivity control. Results from the ERASE code are presented using Grumman's System for IR Evaluation/Contrast Generator Code (SIRE/CONGEN) as input.

This paper suggests a method for normalization of D* for SPRITE detectors with respect to MTF-limiting parameters, primarily the diffusion spread. The purpose of the normalization is to obtain a single performance parameter for the SPRITE detector to make it more objectively comparable with conventional detectors with discrete elements. The recalculation ratio is the rms noise calculated with a filter that compensates the impulse response back to a square pulse divided by the rms noise of the SPRITE element with no compensating filters. In this paper two filters are used: one that fully compensates back to a square impulse response, and one that compensates the MTF at two selected frequencies. The recalculation ratio is calculated as a function of diffusion length with the ratio element length/(carrier life time* scan speed) (L/vt) as a parameter. The results show very little variation with L/vt, so the results should be valid for most applications for the SPRITE detector.

This paper describes the spectral and in-band radiometric imaging of targets and scenes (SPIRITS) modeling software and how it is used to model targets. The target modeled for this paper is a generic aircraft.

A method for measuring imaging system MTF is presented that is compatible with modeling predictions as implemented in the Army's FLIR90/92 static performance model. The method uses commonly available commercial test equipment and personal computers and is effective for measuring scanning and staring array imaging systems in any imaging orientation. Testing accuracy is addressed, and simulation results are presented. Actual test data is also shown and compared with model predictions showing good agreement.

This paper summarizes the discussion of the MRT working group that was held last year at this meeting. As is the case with most working groups, consensus was difficult to obtain. One thing that the group was in agreement about was that MRT is an imperfect figure of merit. In this paper, I present many of the issues that were discussed at the meeting along with my views about what the future holds in store for MRT.

Tests for modulation transfer function (MTF), particularly for staring systems, are affected by the position of the test target with respect to the rows and columns of the detector array. To alleviate the position-dependent nature of the measurement, we have developed a target that uses random patterns of known spatial-frequency content. In this way a phase-averaged MTF is measured, which is indicative of field performance on natural scenes.

The noise equivalent temperature difference (NETD) of forward looking infrared (FLIR) systems is a widely used performance parameter that characterizes the sensitivity of thermal imaging sensors. Although this parameter has been used for many years, there has always been some confusion and misunderstanding about how to measure it. Differences in opinion on how this measurement should be made can cause substantial variations in reported values of NETD measurements. It is the intent of this paper to clearly describe the measurement technique used at Night Vision and Electronic Sensors Directorate (NVESD).

The use of focal plane arrays (FPAs) in infrared imaging systems is becoming increasingly important. There are problems, however, in measuring their modulation transfer function (MTF) and their minimum resolvable temperature difference (MRTD) since these performance measures vary with the exposition of the image on the FPA. This limitation has been overcome through the introduction of a discrete MTF for these imaging systems using discrete Fourier transform techniques. This discrete MTF is a unique function of spatial frequency and has been measured using a microscanned discrete line spread function. It has also formed the basis of an objective MRTD, the results of which have been compared with subjective measurements.

The MBT quantum-well detector is a new generation of detector materials and technology. Quantum-well detectors are based on mature GaAs materials growth and processing technologies that feature large wafers and outstanding material uniformity. These attributes combine to produce an affordable long wave infrared (LWIR) focal plane array (FPA). MBT quantum-well FPAs have demonstrated temporal noise equivalent temperature differences of 15 milliKelvin and operability in excess of 99.5%. The MBT detector can be bandgap engineered for peak spectral response between 3 micrometers and 19 micrometers and bandwidths from less than 0.5 micrometers to more than 4 micrometers . The MBT quantum-well detectors have been hybridized to 128 X 128 silicon multiplexers and are offered as an integrated sensor in the ImagIR, a turnkey imaging platform capable of real-time processing, display and storage of data.

A shipborne infrared surveillance system, which is tasked with detecting real time target trajectories, needs a kinematic evaluation of the cloudy background. In effect, false alarms appear at the cloud edges; these false alarms reducing the effectiveness of the surveillance system. The elimination of clutter by means of static criteria on each frame is not possible because of the spatial coherence of these edges. The interest of this study is to bring together complementary information that concerns the temporal evolution of the 2D infrared signal. Thus the aim is to evaluate the kinematics of cloudy backgrounds. The originality of this paper resides in the use of the Generalized Hough Transform associated with an affine transform method using optical flow computation. The first transform gives an average displacement for a set of pels, while the second extracts more accurately the motion information by means of differential analysis based on the optical flow constraint equation. The complementary aspect of these two methods of motion estimation is shown.

Under the Autonomous Landing Guidance (ALG) Program, personnel of the Avionics and Flight Dynamics Directorates have been evaluating passive infrared and millimeter wave sensors. The goal of this program is to provide transport aircraft with imagery of runways permitting operations without reference to conventional radio-based navigation aids. This paper describes measurements and analysis of the two infrared sensors tested during 1992.

A Scophony Infrared Scene Projector (IRSP) is being used at Wright Laboratories Armament Directorate, Guided Interceptor Technology Branch, Eglin AFB, to evaluate thermal-imaging guidance systems. This hardware-in-the-loop testing system reduces the number of necessary field trials and has potential for in-laboratory simulation where the performance of entire seeker systems can be analyzed. The performance of an optical system, in terms of such characteristics as wavefront error, resolution, and transfer factor, can be measured with knowledge of the system MTF and PSF performance. A slow-scan calibration system was used to measure an image plane of the IRSP under three separate configurations of the system. MTFs and PSFs were derived for the IRSP without the use of the scatter screen, with the scatter screen in place, and with the scatter screen rotating.

Two Triband Imaging Infrared Radiometers (TI²R) were designed and fabricated for the U.S. Army Strategic Defense Command by Automated Sciences Group, Inc. The first TI²R system was designed to perform hardware-in-the-loop (HWIL) simulations using a laser scene projector and electronic signal injection. The second TI²R system was designed for field testing to provide validation data for the HWIL simulation. This paper describes the design and operation of these two systems and the HWIL testing that was performed.

The Arnold Engineering Development Center (AEDC) has developed new test technologies and methodologies for realistic mission simulation testing of infrared space-based sensors. These technologies and methodologies have been combined into an integrated approach for space sensor testing. This approach integrates component, subsystem, and system level tests. Computational models are used to address both sensor optic and chamber optics effects. Simulations and real-world phenomenology are used to generate scenarios tailored for each specific orbit, mission, threat, etc. The synergism of test technology and sensor design characteristics is evaluated and integrated into the test process in order that issues ranging from radiometric calibration to overall mission performance may be properly addressed. A case study based on AEDC's Direct Write Scene Generation (DWSG) test technology is used to illustrate this integrated approach.

This paper examines the focal plane for the proposed Brilliant Pebbles sensor. Each Pebble is designed to be autonomous -- to locate and identify thrusting targets, determine which it can reach, and to attempt to intercept the closest target. Tracking a booster is not possible with a single sensor, so each Pebble identifies targets by comparing the measured intensity histories with those for known targets. The proposed focal plane has a large dead space between detectors. The detected target intensity thus varies dramatically as the target moves across the focal plane, even when the target intensity is a constant. Intensity measurements can thus be extremely inaccurate. The effect is studied for several fill factors, from 100% down to 50%, the approximate fill factor for the proposed system. Knowing the precise position of the blur spot on the detector helps to compensate for this effect. One method, which estimates position using intensities from adjacent detectors, is shown. But this method's value declines as the fill factor decreases. Furthermore, the method can only work when the detector response as a function of target position is known precisely. The effect of the focal plane design on separation of closely-spaced objects (CSOs) is derived. Several cases are shown in which multiple targets, separated by substantial fractions of a detector width, are indistinguishable from a single target. The effect of changing the fill factor is also demonstrated. As the fill factor decreases, the effect worsens. Proposed changes to the sensor design include increasing the fill factor and/or defocussing the blur spot. Results are shown for various combinations of these parameters.

Simulation methods offer a time- and cost-effective approach to the evaluation and testing of guided missiles. These include hardware-in-the-loop as well as all-digital simulations which provide information about how a particular existing or proposed missile system might perform in hypothetical situations which may not be practically duplicated in reality. This paper describes an all-digital simulation developed using available components. The paper describes the functional flow of the simulation, and identifies the information which is passed between the independent modules. Several applications are described, and results such as intercept miss distances, line-of-sight pointing error statistics, and sensitivity to certain system parameters are demonstrated.

The defense budget is shrinking. Weapon systems are getting more complex. Test requirements are increasing. The training and war gaming scenarios are getting more demanding as fielded systems and training simulators are integrated to support combined arms training. To cope with these requirements and still stay within the budget, the Department of Defense is relying on modeling and simulation. The state of the modeling and simulation (M&S) art has advanced to the point where a user can now create incredibly realistic, extremely detailed models which can augment test and evaluation, support the acquisition process, enhance training and war gaming, facilitate intelligence gathering, and support detailed engineering.

This paper presents a method for generating quick and accurate background level estimations with corresponding threshold level estimations from a distribution profile of time delay integration (TDI) scanning focal plane array (FPA) detector values. The resulting background and threshold parameters are used to separate target signal contribution from background and noise contributions. This method was developed for use in a real-time multiprocessor based infrared (IR) imaging and signal processing system. The algorithms developed for the system have been designed and tested for detection of small targets. This process for estimating background and threshold parameters is explained along with discussions of performance evaluations and limitations.

In recent years, infrared (IR) spatial light modulators (SLM) have found applications in areas such as scene simulation and dynamic spatial frequency filtering. To help meet these requirements, we have developed two novel methods of SLM fabrication. Both SLM designs deposit a vanadium dioxide (VO₂) thin film on a thermal array. VO₂ films exhibit a temperature dependent hysteresis about their transition from dielectric to conductor. Accompanied with this transition is a change from a state of low to high reflectivity in the 3 - 5 micrometers band. Our two SLM designs exploit this temperature dependent hysteresis through the use of thermal arrays. The first SLM design deposits the VO₂ thin film on a planar diode array. Each diode constitutes a `pixel' of the SLM. Power provided to a diode permits accurate thermal control about the film's hysteresis. Initial biasing of the diode array is required to the base of the VO₂'s hysteresis curve. The second SLM design deposits VO₂ on a thermoelectric array. These pixels have the ability to both heat and cool the VO₂ film, thereby allowing the array to be operated in a bistable mode. Bistable operation requires external biasing to the center of the VO₂'s hysteresis curve.

A high speed digital interface has been developed to accept real time digital pixel data from high resolution CCD cameras. The interface is currently in use with both a 640 X 486 12-bit digital infrared camera operating in non-interlaced mode at 30 frames per second, and a 756 X 484 8-bit digital visible camera operating in interlaced mode at 60 fields per second. Using programmable logic, the interface is reconfigurable to accept digital data from a variety of sensors at data rates of up to 18 megabytes per second. The buffered digital data is recorded on a hard disk array consisting of up to nine individual drives, with a present capacity exceeding 5.9 gigabytes. Continuous recording is achieved by implementing a loop function on the disk array.

We report on the performance of a flat-panel thermal display technology, prototype developed at NIST in collaboration with Simon Fraser University and Optical E. T. C., for dynamic thermal scene simulation (DTSS). The pixel elements of the display are composed of thermally-isolated resistive heaters. The main innovation is the fabrication method which uses commercial CMOS integrated circuit (IC) foundries. This method produces a low- manufacturing-cost, high-yield, thermal display technology. Circuits for drive and control are monolithically integrated on the display. The microheating element has a thermal time constant of a few milliseconds and a temperature range of operation from ambient to over 1000 degree(s)C. A 16 X 16 pixel array with a 0.2 mm pixel pitch is presented as a demonstration of the concept; however, the circuit design supports larger sizes (e.g., 256 X $256). This display technology is compatible with DTSS requirements for laboratory and fieldable built-in test/built-in test equipment (BIT/BITE) applications.

Airborne infrared fire location can be used to augment other techniques for the detection of small, incipient forest fires. Described here is a new real-time spatial/spectral scanner concept, the Adaptive Infrared Forest Fire Sensor, which employs an acousto-optical tunable filter (AOTF), an indium antimonide or similar array detector, and a steerable scan mirror to enhance the probability of detecting small wildfires and to reduce the rate of false alarms caused by variations in the forest scene, atmosphere, and sun position. Rapid switching of the wavelength of operation in response to the received signal permits the scanner system to optimize the spectral information about a particular spatial location. Measurements on a laboratory prototype system are in progress to verify the salient features of the design concept.

This paper discusses the design and development of thin film monolithic thermal infrared detector arrays integrated with signal conditioning and multiplexor VLSI microcircuits on the same silicon chip. The impact of this technology on thermal imager design is considered. Monolithic processing offers the potential for reducing detector cost to that of a microelectronic circuit component, thus opening the way for development of a new generation of lightweight, affordable thermal imagers. A summary is given of the status of uncooled thermal sensor development at the Defence Science and Technology Organisation.

Spatial-frequency filtering of laser speckle patterns has proven to be a useful tool in the measurement of MTF for focal plane arrays. Intensity thresholding of the laser speckle patterns offers nearly an order of magnitude savings in digital storage space. The effect of this thresholding on the spatial-frequency power spectral density of the speckle pattern is investigated. An optimum threshold level is found that minimizes distortion of the power spectrum for the classes of speckle data used for MTF testing.

While several established models exist for estimating human detection/recognition performance of infrared imaging systems, characterizing the performance of autonomous imaging IR system is still in its infancy. This paper proposes a generic scene description metric which uses target and background characteristics to measure the extractability of the target from the background and is equally applicable to the detection, recognition, or tracking problem. A methodology which correlates this metric with ground-truth based system performance to establish critical performance values is then presented. Finally, an integrated model for predicting the overall system performance given user specified scenarios is presented.

The conventional area weighted average temperature (AWAT) (Delta) T is a primary performance measure for characterizing target/background scenes. However, the AWAT definition is widely recognized as being inadequate for representing observer sensitivity in many target detection and acquisition tasks. This situation is particularly true for targets which are at short ranges relative to the observer or viewed through powered optics. In these cases the mid and high spatial frequency components provide distinctive cue features which dominate over the average or aggregate characteristics of the target. The authors examine alternative definitions of (Delta) T in order to identify more robust and accurate metrics for the evaluation of sensor and signature countermeasure performance. The analysis indicates that target/background scene descriptions using simple average parameters such as the mean and standard deviation are not sufficient for characterizing imaging sensor performance against targets with internal texture and contrast gradients in background clutter.