A software developped in C language for a quick field calibration of thermal imagers is presented. The software allows to take into account the atmospheric transmission between the target and the imager, and to evaluate the corrected blackbody radiation temperature of any resolved area on the target at a known range. The software and the field procedure for calibration are described. Some validation tests carried out during the NATO RSG-17 trial in Meppen Germany, and more extensive tests performed at DREV after the trial are also presented. The error budget in calibrating thermal imagers and evaluating both extended and point target signatures from thermal imagery is analysed and discussed.

A room temperature electrical substitution radiometer (ESR) or electrically calibrated null radiometer (ECNR) has been employed to determine the total radiant exitance of a high temperature secondary standard blackbody to illustrate the convenience of a room temperature ESR. Additionally, routine experimental precisions of ±0.13 to 0.05 percent (type A errors) and a derived absolute accuracy of ±0.24 percent (type B errors) for the Stefan-Boltzmann constant determination and ±0.2deg for the blackbody temperature determination have been demonstrated. From the blackbody radiator's temperature, the familiar Stefan-Boltzmann constant is measured within 0.11 percent absolute to the currently accepted value of 5.67051 x 10¹² W-cm^-2-K^-4. Alternatively by applying the accepted Stefan-Boltzmann constant value, the radiator's temperature is derived and shown to be within 0.2 degree at 692.73 K, the zinc freezing point standard and within 0.2 degree at 933.62 K, the aluminum freezing point standard. The uncertainty of the secondary standard blackbody is ±0.2 K following radiometric comparison to zinc and aluminum primary standard blackbodies. By way of introduction, the genesis of 25 determinations of the Stefan-Boltzmann constant, spanning a period of 86 years, is presented to illustrate the evolution of technical advances in analytical methods, the quality of equipment, and refined accuracy.

The principles of a technique for high-speed capture of infrared spectral information of radiation emission are described. The development of the technique has led to instrumentation which has been used in the laboratory and field for the analysis of such events as gun flashes. The optical design features allow the system to measure spectral characteristics up to 1000 times per second from targets at short or long observation ranges. The system has the capability of operation for multi-channeI high speed capture or steady-state radiation monitoring and hence provides a means for target/scene contrast assessment. Measurement data is presented together with an evaluation of signal to noise performance.

When documenting the infrared images of targets and backgrounds it is usually necessary to place one or more sources having known surface radiances within the field-of-view of the imaging system in order to calibrate the imagery. Although a variety of commercially available thermal references (i.e. , "black bodies") exist they generally are very expensive and are not well suited for operating in the field under severe winter environmental conditions. A portable low-temperature thermal reference was recently developed at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) to calibrate infrared images of mines and snow backgrounds in winter.

A novel method for the absolute measurement of both diffuse and specular reflectance using a Fourier transform infrared spectrophotometer with an integrating sphere is presented. By mounting the sample in the center and referencing off the wall of the sphere, total and diffuse reflectance measurements can be made without having to use a reference sample. The specular reflectance is then calculated as the difference between the total and diffuse curves.

It is well understood that the operation of Infrared Systems is influenced greatly by the atmospheric conditions encountered during all levels of Infrared Systems Testing. One such effort to provide this definition is presented in this paper. During the VISION I field test, conducted by the U.S. Army CECOM Center for Night Vision and Electro-Optics, a very thorough network of sensors gathered atmospheric transmission, optical turbulence, solar radiation, and standard meteorological data. A completely computer based system was used to gather the data and present it to the users in a highly tailored and highly useable form. This effort is described, showing a system description with data examples. Data collection is a secondary thrust of this paper. Of more importance is the processing and disseminating (to the various users of the data) which provides a complete ground truth of atmospheric conditions during testing which is usable by system engineers and modelers.

After some 30 years of research, infrared (IR) technology has evolved to a full valued science, caused by the development of new detector materials in particular and by low noise micro electronics in general. Initially requirements for research were mainly defined by scientific organisations and the Military. After a short general introduction to the subject, attention will be given to the characterisation of IR signatures along the lines of model development, to the definition of involved parameters and measurement methodology. After this overview, the topic of 'thermal variation in a natural land background' , which has a growing interest at the moment , will be treated. Especially, time will be devoted to discuss techniques to characterise the thermal behaviour of natural background elements by means of statistical evaluations of point radiometer data, collected over a long measurement period. Next to the point measurements attention will be given to the radiance variation (thermal clutter) in an image, i.e. the (time varying) distribution of IR sources irj position and time.

The fundamental limits of temperature estimation accuracy are computed for a gray body object. Cramer-Rao bounds are computed for both signal host noise and background-limited cases. A procedure is described for obtaining practical limits on temperature estimation for a given optical system and for evaluating sensitivity to system parameters. The applications include multispectral scene analysis, high-speed thermography, and temperature discrimination.

The directional characteristics of surface emittance and reflectance have a significant impact on the radiance of a target. The directional characteristics of a surface are completely specified by the bidirectional reflectance distribution function (BRDF). In this paper a practical implementation of a method for calculating directional reflection and emission using the BRDF for the purpose of simulating infrared scenes is described. The implementation is based on the existing Georgia Tech Infrared Signature Code (GTSIG) and the semi-empirical Sandford-Robeitson BRDF model.

In recent years many electro-optical devices have been introduced into the military community to ensure air transport capabilities at all times and under a wide range of weather conditions, and to allow target acquisition in low visibility, low light level situations. Forward Looking Infrared (FLIR) will be used for navigation in helicopters and fixed wing aircraft. To give weather support to E-O system users a decision aid to predict FLIR performance has been developed. To evaluate FLIR-performance atmospheric transmittance and path radiance have to be addressed, as well as sensor characteristics and background temperatures.

This paper discusses the measurement and characterization of foliage dynamic response and the effect that the response has on scene variability under variable solar loading. A simple model for predicting transient thermal response under dynamic solar loading conditions is presented. The accuracy of the model is experimentally validated using both imaging and nonimaging IR sensors. Image maps and histograms of the parameter distributions are presented and physical interpretations of the parameters are given.

A statistical approach is taken to present and analyze large amounts of physical and radiometric temperature data for structural materials as well as weather data collected over a period of several years at sites in both the United States and Europe. Diurnal temperature curves are presented as a function of time-of-year, surface material type, and surface orientation. Empirical temperature prediction models for different surface types as a function of weather parameters are developed for a given set of data to demonstrate the utility of maintaining large temperature/weather data bases in support of first-principles thermal modeling.

This work describes a new technique that can be used to determine the IR transmittance and path radiance of an obscuring atmosphere. The method is based on alternate measurements of contrast through a clear and obscuring atmosphere respectively. An advantage of this technique is that it utilizes existing thermal imagers and does not require an additional transmissometer in the field. The technique was tested using an AGEI4A 780 Thermovision camera operating in the 7.7-13.2 micron spectral region. A good agreement between theory and the experimental results was obtained.

The detectability of ground targets in both the visual and thermal infrared spectral regions is dependent on the details of the vehicle's signature and the characteristics of the scene background. Commonly used signature characteristics, such as visual contrast or thermal temperature contrast, are insufficient for use in the sensor and countermeasure systems. This paper discusses the use of an imaging simulation approah to address this difficulty.

Current engineering-level smart munition sensor models emphasize sensor/target interactions with detection and aim-point information being the principal outputs. Background is not treated with the same fidelity. False alarm rate is based on captive flight statistics and is not actually simulated. The lack of a means to evaluate effects of background in an end-to-end simulation mode motivated the development of the WES Smart Munition Thermal Sensor Model. The model consists of a generic set of algorithms used to simulate platform dynamics, scanning geometry, and infrared sensor optics and electronics. Thermal target models of a vehicle developed by Georgia Tech Research Institute are instantiated into a background scene consisting of calibrated thermal imagery. Parameters are set to reflect the flight dynamics, scanning, optics and electronics of a specified munition, and the output voltage is processed though an appended target acquisition algorithm. A hypothetical smart munition with a thermal sensor (simple flying spot detector) is configured and flown over high-resolution thermal imagery obtained from selected locations to demonstrate effects of varied terrain and environmental conditions.

The performance of the Tactical Environmental Support System FUR tactical decision aid program UFLR was reported upon previously. In using this code it was assumed that the temperature difference between ship and sea is fixed. In actuality the temperature difference changes with sea state, aspect, cloud cover, and visibility conditions. In this article a simple predictive temperature contrast taking these effects into account is described and validated against experimental data. A modified ThA code UFLRB including this input is compared with observed ranges. The modified procedure shows up to 36% improvement in detection range prediction at night.

The test hardware of the Automated Imaging Infrared Seeker Performance Evaluation System (AIISPES), a facility being established to support the next generation of Army seekers, is described. The test enclosure, blackbody collimator, target wheel, seeker test fixtures, optical alignment bench, space frame optics, and computer system are examined. The future capabilities of the AIISPES facility to conduct static dynamic, and field test are addressed.

Using the FASTSIG signature code to generate optical signature databases for the Ground-based Surveillance and Traking System (GSTS) Program has improved the efficiency of the database generation process. The goal of the current GSTS database is to provide standardized, threat representative target signatures that can easily be used for acquisition and trk studies, discrimination algorithm development, and system simulations. Large databases, with as many as eight interpolalion parameters, are required to maintain the fidelity demands of discrimination and to generalize their application to other strateg systems. As the need increases for quick availability of long wave infrared (LWIR) target signatures for an evolving design4o-threat, FASTSIG has become a database generation alternative to using the industry standard OptiCal Signatures Code (OSC). FASTSIG, developed in 1985 to meet the unique strategic systems demands imposed by the discrimination function, has the significant advantage of being a faster running signature code than the OSC, typically requiring two percent of the cpu time. It uses analytical approximations to model axisymmetric targets, with the fidelity required for discrimination analysis. Access of the signature database is accomplished through use of the waveband integration and interpolation software, INTEG and SIGNAT. This paper gives details of this procedure as well as sample interpolated signatures and also covers sample verification by comparison to the OSC, in order to establish the fidelity of the FASTSIG generated database.

Target detection in clutter depends sensitively on the spatial structure of the latter. In particular, it is the ratio of the target size to the clutter inhomogeneity scale which is of crucial importance. Indeed, looking for the leopard in the background of leopard skin is a difficult task. Hence quantifying thermal clutter is essential to the development of successful detection algorithms and signature analysis. This paper describes an attempt at clutter characterization along with several applications using calibrated thermal imagery collected by the Keweenaw Research Center. The key idea is to combine spatial and intensity statistics of the clutter into one number in order to characterize intensity variations over the length scale imposed by the target. Furthermore, when properly normalized, this parameter appears independent of temporal meteorological variation, thereby constituting a background scene invariant. This measure has a basis in analysis of variance and is related to digital signal processing fundamentals. Statistical analysis of thermal images is presented with promising results.

A methodology is presented for estimating the impact of meteorological conditions on the detection of airborne targets by a naval surface-based IRST system. This is accomplished by linking a target signature computer code to a weather data base and collecting target contrast signature statistics as a function of target range. System performance is determined by comparing the IRST detection requirements to the signature statistics. Calculations are presented for both a mid and long-wave sensor operating in the North Atlantic. At this location, the long wave sensor is found to provide better detection performance owing to more favorable target spectral characteristics and a generally greater atmospheric transmittance.

The NPS-IRST,a modification of the Advanced Demonstration Model of the Navy AN/SAR-8 InfraRed Search and Target Designation system, mounted in a rooftop location at the Naval Postgraduate School, Monterey, has been used to record background scene information. High data-rate tape-recording with reduced-rate playback is used for data processing and a 'framegrabber' board for image display and processing. Irradiance probability density function, pulse width probability density function, and autocorrelation function plots are displayed for five background types selected from false-color image displays.

Shore based ocean sky and sea radiance measurements from the Navy Background Measurements and Analysis Program (BMAP) and the Infrared Analysis Modeling and Measurements Program (IRAMNP) are used to evaluate an ocean infrared radiance model. The SEABEAN model uses LOWTRAN VII for sky dome radiance calculations and atmospheric transmission, and the Cox-Munk wave slope statistics coupled with the Saunders wave shadowing model. The model results were found to be in modest agreement with the experimental measurements. Results were improved through plausible adjustments to uncertain meteorological test parameters.

The mission of the Individual Protection Directorate of the U. S. Army Natick Research, Development and Engineering Center is to develop clothing and equipment to protect the individual combat soldier against battlefield chemical, ballistic, surveillance, environmental and nuclear hazards. In an effort to meet our countersurveillance mission, the Terrain Analysis Systn was developed by Natick in conjunction with Decilog, Inc., Melville, New York. The Terrain Analysis System was developed to satisfy the need for a scientific method of designing camouflage patterns based on natural terrain reflectance data. It functions as a portable, abridged spectrophotometer to obtain spectral refltance data in the visible and near-infrared on any scene of interest. Data is collected on videotape in the field, digitized into the computer back in the laboratory, and spectral reflectance factors determined for each pixel in the scene. The 1976 CIE L*a*b* color coordinates are calculated and the image is clustered to a user-specific number of color domains. Camouflage patterns can be designed based on these domains, and visual camouflage evaluations can be made by overlaying the designed patterns on any desired background scene. Additional capabilities include calculation of values analogous to the CIE values, which use infrared film or an image intensifier as the observer. The Terrain Analysis System is also capable of analyzing video data taken through an image intensifier or thermal imager and calculating the probability of detection of a user-defined target against the background. "What if" cases can be run to determine the detection probability under other sets of conditions, such as a detector with a different spectral response or under different atmospheric conditions.

Understanding the general statistical characteristics and the distribution of target-like features in thermal background imagery is an important part of solving the automatic target recognition (ATR) problem. An alternative approach to test site and scene characterization, based on thermal background image metrics, is described and demonstrated. A database of forward looking infrared (FLIR) imagery, and meteorological and terrain data was systematically obtained from three continental U.S. (CONUS) test sites. Image metrics, relevant to ATR performance, were computed on all imagery. It was demonstrated that temporal variations in these metrics could be predicted (r²≥0.79) using current meteorological conditions and a time history of solar loading measurements. Scene-to-scene differences in the texture metrics at a single test site could be predicted (r²≥O.78) based on gross scene content attributes. The applications and limitations of this approach and procedure are discussed.

Scene generators are discussed in the context of sensor system tests, and practical experience in their use are highlighted which indicate that a universal scene generator which is good for all applications does not exist. Scene generator requirements are examined, and it is shown that several scene generators need to be incorporated into a specific test pallet.

This paper addresses the development of an Infrared Scene Simulator for Hardware-in-the-loop simulation of tactical IR air-to-air missile seekers. The simulator uses infrared target and background images produced by several technologies which are optically combined, collimated, and presented to the seeker under test. The system is configured for use on an optical bench but could also be hardened for flight simulator mounting. The high radiance target images of the air-to-air engagement scenarios are generated using high temperature blackbody sources and iris targets in the form of geometric figures with the size under servo control. The targets use an X-Y translation slide and dynamic attenuator to simulate movement within the field of view, range closure and the attenuation effects of the atmosphere. These targets are used to generate the aircraft tailpipe and flare decoy images required by the simulation. The high radiance targets are combined with the image from a Multiple Dynamic Simulator-Infrared Emitter Array which produces the engine plume, aircraft fuselage and background image. The three targets are combined using two beamsplitters and the composite image is collimated and relayed to the seeker under test. A workstation-based computational system generates the array image for display in real time.

A Scophony Infrared Scene Projector (IRSP) is being developed for use in evaluating thermal-imaging guidance systems. The Scophony IRSP is configured to be a very high frame rate laser-scanned projection system incorporating Scophony modulation. Scophony modulation offers distinct advantages over conventional flying-spot scanning, for example, longer pixel dwell times and multiple pixel projection. The Scophony IRSP serves as the image projection system in a 'hardware in the loop' therminal-phase guidance simulation. It is capable of projecting multiband, target engagement scenarios with high fidelity using Aura's proprietary software/electronic control system. The Scophony IRSP utilizes acoustooptical (AO) devices to produce the required imagery at four separate wavelengths simultaneously. The four separate scenes are then combined and projected into the imaging guidance system.

The Low-background Scanning Point Source (LSPS), a field-portable low-background target generator designed to allow vehicle-level ground test and checkout of infrared seekers, is discussed. The LSPS can be used to simulate a room-temperature point source moving at a constant rate against an exoatmospheric background or as a point-source calibration change. It incorporates a cryogenically cooled off-axis Gregorian collimator and a dual-axis scan mirror viewed through a zinc selenide window. An analysis is presented of its optical and radiometric performance, and its integration to the vehicle is discussed.

It is possible to generate synthetic images of the sea by creating a sea relief and by calculating its image using raytracing techniques. The sea surface is generated using sea wave statistics which are wind speed and direction dependent. A known power spectrum of the sea wave is used to filter white noise and the filtered noise is used as the sea relief. After that, the image of the sea is calculated using a ray-tracing technique which considers the emitted radiance of the sea, the specular reflection of the sky radiance and the reflection of the sun radiance (which is the sun irradiance scattered by the atmosphere). The resulting sun glint has been compared with the Cox and Munk model in order to make final adjustments to the simulation parameters. Thus, this model is able to produce images with well calibrated radiance and good sun glint distribution.

Since it was first introduced to the public in the early 1980's, the Lockheed Sensor Test Facility (STF) in Sunnyvale, California, has undergone a dramatic transformation from a highly labor intensive experiment to a fully automated, state-ofthe-art production LWIR sensor calibration laboratory. Radiometric traceability is assured with the first blackbody calibration by the National Institute of Standards and Technology (NIST-formerly NBS), and the optical system has been thoroughly revamped to provide diffraction-limited performance in the infrared at wavelengths above 6 μm for LWIR sensors with input apertures to 15 cm. New, modern refrigeration equipment has been added, and the vacuum system has been thoroughly overhauled to provide a simulated exoatmospheric environment as low as 20 K absolute temperature and 10^-8 torr absolute pressure. This report traces the evolution of the STF during the last two years, and details the many enhancements and capabilities introduced in that period. The results of a two-year characterization and calibration activity are summarized, and a full description of capabilities and services available to the LWIR sensor community is included.

This paper discusses a Dual Mode Hardware-in-the-Loop simulation facility developed for the dynamic evaluation of IR/RF dual mode seekers. A unique concept combines the collimated target images from an Infrared Scene Simulator and an RF Target Projector using an IR/RF "dichroic" and reflects/transmits to the seeker under test. The combined IR/RF target scene generator is mounted on a two axis target motion simulator. The dual mode seeker is mounted in a three axis flight simulator, allowing the missile-to-target scenario to be simulated across wide dynamic conditions. The paper will discuss the Infrared Scene Simulator including the design constraints due to the physical/dynamic operating environment, the target characteristics, and the properties of the IR/RF target combining dichroic. The RF Target Projector will be described including the design goals for range performance, and the RF feed horn system. System performance characteristics will be described including computer simulations of the RF Target Projector performance and laboratory tests of the Infrared Scene Simulation.

Interferometric visualization of the turbulent structure of a simulated high velocity mixing/shear layer has been achieved using a pulsed laser shearing interferometer. This technique has the advantages of being simple to implement, relatively insensitive to vibration, and capable of recording many interferograms during each test run. Visualization of the structure of these flowfields enables experimental determination of the turbule dimension, distribution, and relative spatial density. This makes possible the calculation of the correlation length and other flow parameters for more accurate experimental predictions of the aero-optic effects such as image jitter, boresight error, blur growth, and transmission loss.

The concept of T* is introduced as a special kind of average foreground temperature. It is shown that weighting for this average depends on the projected solid angle of different items as seen from the measurement target. It is shown that T* considerations are important for most radiometric measurement tasks. The relationships among radiometry, cavity radiation theory, and T* are shown.

In this paper, double surface pyrometer, one with a preceded reflector and another with a preceded absober, are used to measure on-line true temperatures and emissivities of the oxided steelplate and a kind of paint. The main error in the measurement of emissivities comes from the temperature increase of the thermosensor with the preceded absober.When the temperature of the absorber is 40°C and the temperature of the measured surface is above 400°C, the Systematic relative error measuring emissivity is less 5%.

A gravity-type heat pipe blackbody source is described. The simple construction of the pipe involves condensed liquid flowing back to the evaporation zone under gravitational influence. The temperature distribution of the cavity walls is very even, with a maximum temperature difference of less than 0.6 C. The effective distribution of the double-cone construction is calculated, and it is found that the effective emissivity at the working area is over 0.999.

In order to study the radiation characteristics of a compound-cavity blackbody, a method for calculating the integrated emissivity is presented in this paper. With this method, firstly, the distribution of the effective emissivity of the sub-cavity of a compound-cavity is calculated; secondly, from the distribution of the effective emissivity, the integrated emissivity of the walls of the sub-cavity to the mouth of the sub-cavity can be obtained; and thirdly, the integrated emissivity of a compound-cavity blackbody is calculated. Employing this method, we calculated the integrated emissivity of a compound-cavity blackbody and analysed the results. The analysis shows that this method is feasable and satisfactory.

Precise calculation of integrated emissivity of a multiple-celled large-area blackbody source has been a very complex problem. The kernel of the problem is to compute radiant exchange between the sub-cavities and a non-coaxial detector. On the basis of the method for computing radiant exchange between a cavity and a coaxial detector, a method has been developed in this paper to calculate the noncoaxial radiant exchange by which the integrated emissivity of the multiple-celled large-area blackbody source was computed accurately. The emitting area of the blackbody is of 200x200 ma that includes more than 1600 sub-cavities.

Many commercially available infrared imagers utilizing mercury-cadmium-telluride scanning detectors are not optimized for long pathlength atmospheric research. At imaging ranges of 1 or more kilometers, path radiance due to emissions from atmospheric constituents such as H₂0 and CO₂ can be a significant contributor to a poor signal to noise ratio. Through proper doping of the detector and cold finger filtering, there is an increase in the magnitude of the propagated, system weighted target radiance and a much more favorable ratio of propagated target to path radiance which directly affects the image quality. Thus, it is necessary when optimizing an imaging system to consider both atmospheric path radiance and detector response. This paper presents a methodology which has resulted in a computer program which provides such optimizations. A first generation modification has been developed at the Atmospheric Sciences Laboratory and preliminary results show an enhancement of target to background apparent temperature or delta T in the 8 to 12 micron region. In the 3 to 5 micron region, it was readily apparent that the modification did not achieve the desired results (especially during winter weather conditions). In order to provide a solution to this problem, a technique was developed to characterize the detector response without the necessity of its removal from the system.