Proceedings Volume 1488

Infrared Imaging Systems: Design, Analysis, Modeling, and Testing II

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Proceedings Volume 1488

Infrared Imaging Systems: Design, Analysis, Modeling, and Testing II

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Volume Details

Date Published: 1 September 1991
Contents: 9 Sessions, 44 Papers, 0 Presentations
Conference: Orlando '91 1991
Volume Number: 1488

Table of Contents

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Table of Contents

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  • Poster Session
  • Infrared System Analysis and Modeling I
  • Infrared System Analysis and Modeling II
  • Infrared System Analysis and Modeling III
  • Infrared System Analysis and Modeling IV
  • Engineering Problems and Solutions Workshop
  • Infrared System Testing
  • Infrared System Design
  • Sprite Detectors
  • Infrared System Analysis and Modeling IV
  • Poster Session
  • Infrared System Analysis and Modeling I
Poster Session
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New type of IR to visible real-time image converter: design and fabrication
Fangkui Sun, Mao-hua Yang, Shao-hong Gao, et al.
This paper presents a new image decomposition scheme that utilizes coding of convex hulls corresponding to a set of order statistic filters. The encoding of convex hulls can be done more efficiently than the encoding of the original image especially when the boundaries of the encoded set are rough.
Design and performance of a PtSi spectroscopic infrared array and detector head
The design and performance of a new 1024-element PtSi IR linear array and detector head available from EG&G Reticon are described. The self-scanned Schottky barrier detector array provides a 1.1 to 5.0 micrometers spectral response, 60% fill factor, 25 micrometers pitch and 100:1 slit-like aspect ratio for efficient coupling to laboratory spectrometers. Pixel-to-pixel non- uniformities of 0.4% rms and saturation charge levels of 9 picocoulombs are achieved. The LN2-cooled detector head used to house the array features a fast focal ratio, short window-to-detector separation and quasi-standard mounting flange. Both analog video and temperature sensing outputs are provided. Timing may be internally or externally controlled. In the former mode, only +/- 15 VDC and +5 VDC power inputs are needed. In the latter mode, external clock and sync inputs as well as power are required. The sensor, dewar, and coldshielding is described; as well as the analog, digital and temperature sensing electronics. A discussion of system-wide performance data and technical specifications concludes the review.
Physical foundations of high-speed thermomagnetic tuning of spatial-temporal structure of far-IR and submillimeter beams
Alexander V. Shvartsburg
The Electro-Optics Laboratory of the Institute for Space and Terrestrial Science characterizes array detectors under a wide range of operating conditions in a test facility based on a uniform optical source, a flexible array controller, a cryostat, and comprehensive and data acquisition hardware and software. Source characteristics, ambient temperature, clock/bias parameters, and output signal conditioning can be varied to maximize the useful information about the devices under test. Emphasis has been placed on achieving a high level of accuracy and reproducibility in the measurements. Results from representative CCD arrays are used to illustrate design highlights and facility capabilities.
ISTS array detector test facility
The Electro-Optics Laboratory of the Institute for Space and Terrestrial Science characterizes array detectors under a wide range of operating conditions in a test facility based on a uniform optical source, a flexible array controller, a cryostat, and comprehensive and data acquisition hardware and software. Source characteristics, ambient temperature, clock/bias parameters, and output signal conditioning can be varied to maximize the useful information about the devices under test. Emphasis has been placed on achieving a high level of accuracy and reproducibility in the measurements. Results from representative CCD arrays are used to illustrate design highlights and facility capabilities.
MTF characteristics of a Scophony scene projector
Eric F. Schildwachter, Glenn D. Boreman
The Scophony scene projector has been examined in detail. Modulation transfer function was measured and found to be significantly lower than expected. The discrepancy is shown to be due to variation in the Bragg angle with input frequency. Experimental data is compared with calculated performance.
Design of an athermalized three-fields-of-view infrared sensor
David R. Wickholm
Design methods and predicted performance of an afocal field-of-view changer for an existing IR camera operating in the 3-5-micron atmospheric transmission region are described. The athermalized changer is predicted to maintain focus within the 1/4 wave criteria over -40-60 C temperature range.
ISOCAM: a camera for the ISO satellite optical bench development
Danielle Auternaud
ISOCAM, a camera to be flown onboard the Infrared Space Observatory (ISO) satellite of the European Space Agency, is described. The camera consists of three parts: an optical bench located at the telescopes's focal plane over a support platform, within the cooled portion of the spacecraft; lukewarm electronics fitted to the Cryostat's walls; and hot, processing electronics located within the service module, over the Cryostat's exterior. The ISOCAM camera uses two channels that cover either 2.5 - 5.5 or 4 - 17 microns bands.
Infrared System Analysis and Modeling I
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Update on the C2NVEO FLIR90 and ACQUIRE sensor performance models
Luke B. Scott, David M. Tomkinson
The C2NVEO FLIR90 thermal imaging systems model released in June 1990 has become the community standard model for evaluating tactical FLIR systems. This model, which successfully predicts MRTD performance for first- and second-generation thermal imagers, differs from the 1975 NVEOL thermal model in three critical areas: sampling, noise, and two-dimensional MRTD. This paper explains how each of these effects is modeled in FLIR90. First, the paper discusses how the model incorporates sampling effects by imposing Nyquist frequency limits and using pre- and postsampling MTFs. Second, the treatment of directional noise and modifications to the NETD prediction is discussed. Third, the paper discusses the two-dimensional MRTD methodology and the adjustments it imposes on the Johnson range performance prediction methodology modeled in ACQUIRE. Additionally, changes and additions in forthcoming upgrades to both FLIR90 and the ACQUIRE range performance model are described.
Three-dimensional analysis framework and measurement methodology for imaging system noise
John A. D'Agostino, Curtis M. Webb
Modern imaging sensors incorporate complex focal plane architectures and sophisticated post- detector processing. These advanced technical characteristics create the potential for multi- component noise generation which can exhibit effects temporally as well as along the vertical and horizontal image directions. Such complex three-dimensional (time, vertical, horizontal) noise cannot be adequately treated by previous mathematical analyses developed for simpler system designs where detector noise was predominant. In a parallel sense, earlier methods for noise measurement are no longer satisfactory. A new methodology has been developed at C2NVEO to characterize the noise patterns exhibited by advanced thermal imaging systems. The methods represents a significant expansion of the standard techniques to characterize thermal system noise. This paper explains the principles behind the 3-D noise methodology and the methods used. It also describes how this methodology is implemented in a laboratory measurement environment.
Solutions to modeling of imaging IR systems for missile applications: MICOM imaging IR system performance model-90
Philip R. Owen Jr., James A. Dawson, Eric J. Borg
The U.S. Army Missile Command (MICOM) Imaging IR System Performance Model code, version 1990, (MIISPM-90), is described. MIISPM-90 provides state-of-the-art modeling of thermal imaging systems using the conventional FLIR modeling methods which can accurately predict performance for standard serial/parallel systems. It also provides full integration of the sensor models with the atmospheric and target models. MIISPM-90 is capable of modeling systems which use SPRITE, Schottky Barrier Diode, scanning FPA, and staring FPA technologies.
Infrared System Analysis and Modeling II
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Multisensor analysis tool
Frank W. Gerlach, Daniel B. Cook
The multisensor analysis tool (MSAT) was developed as a software aid for the design and parametric analysis of electro-optical sensors and multisensor suites. An executable version of MSAT is uniquely specified by combining a generic window-based shell with user-supplied sensor knowledge. The application-independent shell utilizes buttons, pull-down menus, plots, on-line help, and a spreadsheet-like interface. Sensor knowledge is supplied by users in the form of those equations which define a model; no programming or debugging is required. MSAT writes source code from this knowledge and links it with the shell. The tool has no concept of either input or output; any parameter may be varied in order to monitor its effects on all other related parameters. MSAT runs on a Sun workstation, comes with full documentation, and has a database which is being continuously populated with new sensor models and knowledge.
Human recognition of infrared images II
Jeffrey S. Sanders, Michael S. Currin
This paper presents the results of psychophysical experiments that addressed human recognition of infrared images. Three experiments are described in which human observers were asked to discriminate between different types of modern armored vehicles at various resolutions. In the original 1950s study, Johnson was concerned with the four criteria of detection, orientation, recognition, and identification, and a limited number of objects was used. This experiment used many more vehicles than Johnson used, but concerns only the tasks of identification friend or foe, and identification. The vehicles are ones that would be commonly encountered in a modern-day confrontation between NATO and Warsaw Pact Forces. Simulated infrared images of these vehicles were presented to trained observers and the resolution thresholds determined. Both signal detection theory and a simplistic percentage approach were used in the analysis of the results.
Infrared systems design from an operational requirement using a hypercard-based program
William R. Harris
A HyperCard-based program, 'IR Assist,' takes the user through the logical steps in designing an imaging infrared (IIR) seeker concept. These steps progress from the postulated target characteristics, to the detector element size, to the errors encountered during missile flight. The IR Assist program was designed for simple database management, common 'what if' calculations, and 'what must be studied in order to complete' questions regarding an IIR seeker concept.
Miscellaneous modulation transfer function effects relating to sample summing
Howard V. Kennedy
Most thermal imaging system performance models do not make provisions for direct input of MTF effects resulting from sample summing, either electronically or on the retina of an observer. Such effects must generally be input as an array of MTF values at matching spatial or temporal frequencies. Both the older NVL static performance model and the new FLIR90 model accept matched pairs of values in this form. One notable example of a sample summing effect is that the misregistration of time delay and integrate (TDI) samples resulting from imaging a moving target. Another is the similar misregistration resulting from an inaccurately known scan rate. Another is the apparent misregistration, on the retina of an observer, of target images when the latencies of different fields of an interlaced image frame are different. Yet another is the smearing of a moving target or scene when samples taken from different interlace fields (and thus at different times) are summed. This paper derives analytic expressions for the effects in question. An example of the proper format in which to input data to the FLIR90 or other performance modeling program is given for each effect.
Infrared System Analysis and Modeling III
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Relative performance studies for focal-plane arrays
Kevin St. John Murphy, Derek J. Bradley, Peter N. J. Dennis
Recent years have seen increasing interest in PtSi infrared imaging systems. The performance and capabilities of a 5122 element PtSi imager have been assessed, and various figures of merit describing system linearity, spatial uniformity, and noise equivalent temperature are presented and contrasted with similar performance figures obtained from a 3-5 micrometers CMT system. The superior spatial uniformity and poorer thermal sensitivity of the PtSi imager is contrasted with the CMT system which generally exhibits poorer spatial uniformity but significantly higher thermal resolution. Trade-off studies between fixed-pattern noise and thermal resolution are discussed in terms of overall system performance for both imagers.
Computer simulation of staring-array thermal imagers
Derek J. Bradley, Peter N. J. Dennis, Chris J. Baddiley, et al.
The recent advances in infrared technology have led to large two-dimensional detector arrays in a range of materials including cadmium mercury telluride, platinum silicide, and ceramic pyroelectric materials. The relatively high temperature sensitivity of these arrays compared with scanned detectors is being exploited in advanced electro-optic equipment either directly or by trading off against other parameters. A major difficulty which faces system designers is that of system performance prediction prior to expensive build and trial phases. In the past, this has been overcome using a number of established computer models which were developed for conventional scanned imagers. However, the principle of operation of staring imagers is so different that a new approach is required. This paper describes a modular computer simulation of staring array imagers.
Recognition criterion for two-dimensional minimum resolvable temperature difference
Howard V. Kennedy
Performance models based on two-dimensional MRTD have been used in the industry for several years. The new C2NVEO thermal imaging model, FLIR90, has been available for almost a year now, and also uses a 2-D MRTD to predict range performance. A two- dimensional MRTD, if used with the same cycle count criteria as the older static performance model, will predict different detection and recognition ranges for any given target. Based on their psychophysical studies, C2NVEO recommends that recognition criteria for the new model be 3/4 of that used with the old model. A brief derivation of the two-dimensional MRT as a measure of resolution capability is presented. The modified criteria is then justified using the rationale of the derivation. A generic common module FLIR is analyzed using both the old and new models, showing how different ranges will be predicted if the same cycle criteria for recognition and detection is used. It is then demonstrated that similar ranges are predicted if the cycle criteria for the two models are set at the ratio of 4:3. A comparison of criteria for several sensors for which actual field measurements exist is also presented.
Validated CCD camera model
Helen Johnson-Cole, Rodney L. Clark
An empirical approach is presented for modeling the performance of a charge-coupled device (CCD) camera. The model described in this paper incorporates experimental results from laboratory camera characterization tests and considers image corruption due to CCD detector array phenomena such as filling inefficiency, blooming, and charge transfer inefficiency. The method treats high-resolution, simulated input images that are generated using a physical, wave-optics code. These generated optical images are input to the CCD model. The resulting camera model predictions agree favorably with experimental images recorded using the actual CCD camera system.
Infrared System Analysis and Modeling IV
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Simulation of sampling effects in FPAs
Thomas H. Cook, Charles S. Hall, Frederick G. Smith, et al.
The use of multiplexers and large focal plane arrays in advanced thermal imaging systems has drawn renewed attention to sampling and aliasing issues in imaging applications. As evidenced by discussions in a recent workshop, there is no clear consensus among experts whether aliasing in sensor designs can be readily tolerated, or must be avoided at all cost. Further, there is no straightforward, analytical method that can answer the question, particularly when considering image interpreters as different as humans and autonomous target recognizers (ATR). However, the means exist for investigating sampling and aliasing issues through computer simulation. The U.S. Army Tank-Automotive Command (TACOM) Thermal Image Model (TTIM) provides realistic sensor imagery that can be evaluated by both human observers and TRs. This paper briefly describes the history and current status of TTIM, explains the simulation of FPA sampling effects, presents validation results of the FPA sensor model, and demonstrates the utility of TTIM for investigating sampling effects in imagery.
End-to-end model for detection performance evaluation against scenario-specific targets
Frank J. Iannarilli Jr., Martin Ronald Wohlers
Aerodyne has recently developed an IRST engagement model under contract for Lockheed Aeronautical Systems Company. The model's purpose is to simulate the performance of an IRST system in long-range air-to-air detection and tracking engagements. The hallmark of the model is its end-to-end first-principles modeling of all major elements which determine specific performance. The target aircraft IR signature, and atmospheric cloud and sky background, and associated atmospheric effects are modeled at high fidelity, thereby producing an input image matched to the specific IRST under study. A detailed deterministic model of the IRST accounts for optical and sensor effects, signal processing, and track association typical of first-generation IRSTs. These model elements are coupled together along with a dynamic target and observer [IRST] trajectories model so that an analyst can specify air-to-air engagements at various velocities, ranges, and viewing angles. The analyst can study the effects of varying IRST algorithms, sensor characteristics, optical bandpass, cloud background levels, atmospheric effects, and target performance characteristics as well as varying the target aircraft itself. This computer model was designed for portability and growth.
Wiener-matrix image restoration beyond the sampling passband
Zia-ur Rahman, Rachel Alter-Gartenberg, Carl L. Fales, et al.
A finer-than-sampling-lattice resolution image can be obtained using multiresponse image gathering and Wiener-matrix restoration. The multiresponse image gathering weighs the within-passband and aliased signal components differently, allowing the Wiener-matrix restoration filter to unscramble these signal components and restore spatial frequencies beyond the sampling passband of the photodetector array. Thus, A multiresponse images can be reassembled into a single minimum mean square error image with a resolution that is (root)A times finer than the photodetector-array sampling lattice.
Computer analysis of signal-to-noise ratio and detection probability for scanning IRCCD arrays
Gianni Uda, Alessandro Tofani
The loss of the energy falling on a IR CCD array due to the effect of finite image size of point targets and of its motion on the focal plane was computed through a Monte Carlo simulation. The aberration-free point spread function (PSF) of the system was supposed to move in the focal plane with spatial steps having an amplitude of the order of the linear scan velocity times the IR CCD integration time. The starting position of the motion was varied randomly near to a reference detector element and each position was assumed to have the same probability of occurrence. By considering the energy integrated by the single detectors it is possible to compute the effective signal-to-noise ratio and the overall detection probability of the system. A new figure of merit, called the spreading factor (SF), can be defined by considering the maximum ratio of the energy integrated by the single detectors to the total energy subtended by the PSF and by taking the average of these maxima over all the random displacements. With the parameters considered in this simulation, the SF turns out to be in the range between 0.2 and 0.5, with a considerable reduction of the corresponding detection range.
Engineering Problems and Solutions Workshop
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Wave-optic model to determine image quality through supersonic boundary and mixing layers
Shelah M. Lawson, Rodney L. Clark, Michele Ruggiero Banish, et al.
Technological advancements in the field of mixing layer theory have allowed the design and subsequent construction of a Table Top Simulator of Aero-Optic Effects. This experimental facility simulates the supersonic boundary and mixing layers formed by the window coolant gas of an optically guided hypersonic vehicle. This paper discusses the foundations of wave-optic theory applied to model the propagation of optical radiation through such flow. The focus of the calculations is to determine performance quality parameters such as Strehl ratio, jitter, 50 percent contained energy diameter and boresight error. These quality measures will drive the performance requirements of the optical system and focal plane array of the seeker. Comparisons are made between wave-optic model results and actual aero-optic data collected from the Table Top experiment.
Infrared System Testing
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What is MRT and how do I get one?
Carl W. Hoover Jr., Curtis M. Webb
Although minimum resolvable temperature difference (MRTD) measurements of forward looking infrared (FLIR) systems have been around for a long time, there is still a lot of confusion and misunderstanding about the measurement techniques. C2NVEO has been performing the measurement since the middle 1970s in its image evaluation facility (IEF). The IEF is generally considered to be the standard of the free world for FLIR measurements. This paper provides a basic understanding of the measurement state-of-the-art of MRTD for first- and second-generation FLIR systems. Concepts and theory behind the measurement are addressed and equipment requirements as well as observer training are reviewed. A discussion of the challenges of evaluating new systems such as staring arrays and second-generation digital FLIRs and the requirements for both horizontal and vertical MRTD measurements is also provided. A discussion of effects at automating the measurement is provided.
Thermal signature training for military observers
Robert LaFollette, John D. Horger
The U.S. Army's CECOM Center for Night Vision and Electro-Optics, C2NVEO, has been conducting a series of human perception tests. These tests score military observers on their ability to identify and recognize thermal images. The results of these tests are used to develop and refine the Night Vision FLIR Performance Model (FLIR90/ACQUIRE). The Thermal Image Training Package is a useful by-product of these tests. It was originally developed to train military observers for perception tests, but the soldiers tested pointed out its value for general training. Since that time, the package has been used by several Army units and has been found to be a valuable asset for training. The Thermal Image Training Package consists of software and imagery designed to quickly teach an observer how to recognize and identify thermal images. It runs on an IBM PC/AT compatible computer with VGA graphics and a hard disk. It loads into a computer in about 15 minutes and a complete training session is self- paced and usually takes less than two hours. It is effective, inexpensive, and simple to use. The package uses actual thermal images, simulated ranges, allows contrast and brightness adjustments, black or white hot polarity, red, green, or gray screen coloring and provides output files of scores for progress checking and analysis. The training package is a useful tool in its present form, but with continued interest and the development of better, cheaper PCs possible future versions have even greater potential.
AutoSPEC image evaluation laboratory
James C. Brown, Curtis M. Webb, Paul A. Bell, et al.
The U.S. Army CECOM Center for Night Vision & Electro-Optics (C2NVEO) is upgrading the existing image evaluation facilities through the AutoSPEC (Automated Sensor/Processor Evaluation Center) program. The image evaluation portion of the AutoSPEC program is a major upgrade which includes entirely new optical systems, instrumentation, and data collection. The design of the laboratory is discussed along with the design and integration of the individual components into a measurement system. The capabilities of the high-speed image capture/processing/storage system will be presented. The design of the control software is also discussed, especially the user interface and the method developed for controlling and automating repetitive measurement tasks. Finally, the test capabilities of the laboratory are discussed. This includes the capability of the system to perform existing figure of merit measurements for wide-field-of-view pilotage systems as well as for narrow field of view targeting systems. New tests based upon the dynamic capabilities of the system are addressed. The flexibility of the system for future capabilities such as realistic scene/target simulation and projection is also addressed.
Reimaging system for evaluating high-resolution charge-coupled-device arrays
Robert J. Chambers, David W. Warren, David G. Lawrie, et al.
Parametric studies of the imaging properties of sensor systems using high-resolution charge-coupled device (CCD) arrays require that the spatial frequency content of the images presented to the CCD be well characterized. We describe a laboratory system based on an all-reflective 1:1 optical relay which provides diffraction-limited images over a useful field up to 100 sq mm area, at any wavelength, at speeds of up to f/5. The design form employed, an Offner relay, has a number of inherent advantages. Additional features have been incorporated for the convenience of experimenters. While presently static, the system can be adapted to simulate scanned sensors. The imaging capability of this relay was verified using a digital camera system built around a large-area (1320 by 1035 pixel), high-resolution (6.8 sq micron pixel size and pitch), Kodak 'megapixel' CCD array.
Reporting data for arrays with many elements
Christopher L. Coles, Wayne S. Phillips, John David Vincent
Figures of merit and data reporting for single-element infrared detectors are well established and easily incorporated in a contractual framework. Measured characteristics which predict system performance regardless of detector type, and which provide useful process feedback have been debated and optimized over the last 50 years. In the recent past these measurements have been extended to small arrays of detectors, which have generally been treated as lists of signal detectors. Arrays of detectors are now routinely tested which have 16,000 elements and proposed production arrays have 256,000 elements. This has rendered traditional methods clumsy and incomplete. Recently these issues have been investigated in order to design a software system to accompany a new IRFPA test system product. The authors describe their view of the requirements, and the approaches that were examined and discarded or incorporated during this effort. Different methods of displaying and reporting data, as well as a calculation engine developed as part of the effort, are discussed.
Determination of FLIR LOS stabilization errors
Howard J. Pinsky
The increasing use of high performance detectors in long focal length FLIR sensors puts a high demand on stabilization systems. In most FLIR designs, the stabilization MTF tends to be the limiting component and has the greatest effect on MRT and range performance. Efforts to improve stabilization results in costly hardware solutions. The verification of the operation of these systems is an important step in the design and development process. This paper details a method for using FLIR characterization tests to measure stabilization system performance thereby verifying the design.
Temperature chamber FLIR and missile test system
W. Todd Johnson, Mosik Lavi, Eyal Sapir
In this paper, we present a methodology for testing Forward Looking Infrared (FLIR) Systems and Missile Seekers in a temperature chamber from -35 to +72 C. Test results show that a single material projection collimator has little to no defocus in this wide temperature range. Blackbody technology is such that a blackbody reference source also shows little to no degradation over this entire range. This technology is a cost saving method which is an alternative to using a collimator system outside of the thermal chamber with a window.
Transient radiometric measurements with a PtSi IR camera
Wayne L Konopka, Michael A. Soel, Anthony Celentano, et al.
Transient measurements in fluid flows are required when the flows are generated by an impulse device such as a shock tube. In our laboratory, a shock tube is used to generate simulated rocket plumes which are investigated for the development/validation of plume signature codes. This paper describes progress in the implementation and use of a PtSi camera to obtain radiometric data in test time periods that are less than conventional frame rates for such devices. Optical modifications and implementation of the camera as an absolute radiometric detector are presented. Overall camera performance in terms of system noise and dynamic range is assessed, and sample plume images in the H2O band centered at 2.8 microns are shown. Future system improvements and measurement program capabilities are mentioned.
Infrared System Design
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High-resolution thermal imager with a field-of-view of 112 degrees
Tadashi Matsushita, Hiroshi Suzuki, Satoshi Wakabayashi, et al.
A thermal imager with a full field of view (FOV) of 112 deg has been developed. An F/1.2 optics with a cold aperture stop and a 512 X 512 element PtSi Schottky-barrier focal plane array (FPA) is used. The influence of internal radiation and ghost images on the performance of the thermal imager has been modeled and analyzed. Experimental results have demonstrated that this imager can be used without saturation even at the ambient temperature above 60 degree(s)C, and the solar radiation incident will not affect image quality significantly. Examples of imagery obtained with high angular resolution less than 4 mrad are also presented. From these results, it has been clarified that the presented models are effective for analyzing the thermal imager performance.
Multiplexed mid-wavelength IR long linear photoconductive focal-plane arrays
James F. Kreider, Mark K. Preis, Peter C. T. Roberts, et al.
This paper discusses the successful demonstration of a first in thermal imaging with utilized an inexpensive midwavelength IR (MWIR) linear, focal plane assembly (FPA) comprising a long linear array of lead selenide (PbSe) photoconductors interfaced to an on-focal-plane multiplexer (MUX). The design of this unique IR sensor consisted of a rugged dewar package in which was mounted a reliable, solid state thermoelectric cooler (TEC) coupled with the proven technologies of both the PbSe fabrication process and the complementary metal-oxide- semiconductor (CMOS) multiplexers. This combination of components now provides the system designer with a readily available, cost-effective, second-generation PbSe focal plane assembly for scanning, thermal imaging applications that require high resolution and system performance of NE(Delta) T capability of better than 0.2 degree(s)C.
Advanced real-time scanning concept for full dynamics recording, high image quality, and superior measurement accuracy
Kjell M. Lindstrom, Bo Wallin
This paper presents the AGEMA idea of a modern, versatile, high-performance thermographic system made for high-definition imaging measurement.
Enhanced thematic mapper cold focal plane: design and testing
Bing T. Yang
The cold focal plane for the Enhanced Thematic Mapper (ETM) contains three spectral bands: two 16-element PV InSb bands and one 4-element PC HgCdTe band. The paper discusses the design of the entire analog video chain which includes detectors, preamplifiers, and the postamplifiers. The PV bands have a 52-kHz signal bandwidth and the PC band has a 13-kHz bandwidth. A semiautomated test set with a modulated GaAs LED for transient optical inputs, was designed to measure the stringent performance requirements in both the frequency response and transient response. The paper shows some of the test results.
Fixed-pattern-noise cancellation in linear pyro arrays
Subhash C. Jain, H. S. Malhotra, K. N. Sarebahi, et al.
The signals from the alternative scans of a chopped cw radiation are of opposite polarities. The output of each scan from a linear array of detectors is digitized and stored in a memory. The output from the successive scans are delayed and added in phase. An inverter switch operating in synchronism with chopper inverts outputs of alternate scans and provides a sequence of signals of the same polarity. The signals of opposite polarities from alternate scans are thus also added in phase and doubled. The fixed pattern noise of opposite polarity from the alternate scans are cancelled. A reduction of more than 20 dB in the fixed pattern noise has been obtained.
Sprite Detectors
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SPRITE detector characterization through impulse response testing
Barry K. Anderson, Glenn D. Boreman, Kenneth J. Barnard, et al.
An impulse response test and data evaluation method for characterizing a SPRITE detector capable of determining carrier lifetime, ambipolar mobility, carrier drift velocity variation, and detector limits is presented. The data obtained with the method can be used to optimize imaging system performance or to tailor future detectors from the same material lot. Results for a 3-5 micron detector bar, 650 microns long with a 62.5 microns horn geometry readout are reported.
Sine wave measurements of SPRITE detector MTF
Kenneth J. Barnard, Glenn D. Boreman, Allen E. Plogstedt, et al.
A method is presented for measuring the modulation transfer function of SPRITE detectors with a HgCdTe composition optimized for the 3-5 micron band. This method incorporates a 3.39-micron HeNe laser to generate Young's fringes of varying spatial frequency, which are scanned across the detector elements. The results are consistent with theoretical models for these devices and indicate a limited resolution capability for SPRITEs used for the 3-5 micron band.
Optimum choice of anamorphic ratio and boost filter parameters for a SPRITE-based infrared sensor
The ringing in the impulse response for a SPRITE based thermal imager is analyzed. The optimum choice of anamorphic ratio and boost filter parameters is derived under a constraint for maximum ringing in the impulse response. It appears that the optimum value for the anamorphic ratio is about 1.4 and that it is optimal to have a boost that gives the maximally allowed percentage of ringing.
Analysis of the flying light spot experiment on SPRITE detector
Boqi Gu, Wen Qing Feng
This paper shows some results about the variation of the SPRITE's line spread function(LSF) with the detector bias current by the flying light spot experiment and analyses the relation of the parameters, which are detector modulation transfer function(MTF), minority carriers lifetime and bias current. The results obtained indicate the performances of the SPRITE detector have not been used optimum appling the bias current (I = 3 mA) at the pixel S = I .8x 106 , It is difficult to improve the efficiency of the SPRITE detector application for the high performance thermal imaging system by increasing pixel or adjusting detector geometry figure.
Infrared System Analysis and Modeling IV
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Development and analysis of a simple model for an IR sensor
Edward A. Ballik, William H. Wan
In the past, a substantial amount of engineering analyses were performed using standard office-style spreadsheets. However, advanced engineering and scientific software such as MathCAD are now available. This paper demonstrates the ease and simplicity of creating powerful workfiles using this software. As an example, a workfile is described which is used to perform basic IR sensor system analyses and development. Several system parameters are analyzed, including blackbody radiation for radiometry, diffraction-limited blur spot and MTF estimation, and arbitrary figure of merit (i.e., target-to-background signal contrast). The paper also discusses the application of the method to more complicated optical systems and analyses.
Poster Session
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Assessment of the optimum operating conditions for 2-D focal-plane-array systems
Robert W. Bourne, E. A. Jefferys, Kevin St. John Murphy
Various companies are now producing 2-dimensional CMT-Si hybrid focal plane arrays. These are complex devices and at present the accepted figures of merit describing the arrays vary significantly between devices of the same type. In infrared imager applications the spatial uniformity of the detector array, particularly with regards to parameters such as noise equivalent temperature difference (NETD) rather than the quality of individual pixels may determine the overall system performance. A small number of unresponsive elements can be effectively masked by correction algorithms in the imager electronics. Assessment apparatus capable of storing the output of all the photodiodes in a focal plane array up to 128 X 128 pixels in size has been used to determine the optimum operating point for three co-ordinate addressed devices, giving rise to a methodology for setting up this type of detector.
Radiometric versus thermometric calibration of IR test systems: which is best?
Radiometric calibration of military IR test equipment is an approach being explored to avoid perceived shortcomings of traditional thermometric calibration. This issue has profound impact on the testing of military systems: the lack of internally consistent calibration architecture can cost military customers millions of dollars in increased maintenance and spares costs due to test result inconsistencies. An example is presented to show that the lack of a standard spectral response definition in this region, and the difficulty in making such a definition, make the radiometric calibration approach seem questionable for the foreseeable future. Calibration errors of more than 7% (not even a worst-case scenario) can result. The best approach to assuring test accuracy and calibration consistency is to employ thermometric calibration in conjunction with intelligent test system design: high, flat spectral transmittance of the test system and high emissivity targets and sources. These are achievable today with proper application of existing materials and coatings.
Infrared System Analysis and Modeling I
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Effects of phasing on MRT target visibility
MRT target visibility is affected by the relative phase between the target location and the sampling lattice of thermal imaging systems. Undersampled systems such as staring arrays are particularly susceptible to phasing effects. For input spatial frequencies which range from 0.6 to 0.9 times the Nyquist frequency, bar fidelity is lost and the MRT is increased at these spatial frequencies. In apparent contradiction to Nyquist theory, it is possible to perceive MRT targets whose spatial frequencies are between Nyquist and 1.1 times Nyquist frequency.