There remains a wide proliferation of second-generation frequency-modulated conical-scan seekers in the hands of irregular forces while the understanding of what makes a jam signal effective remains unclear. It is generally known that the jam-to-signal (J/S) ratio, the jam signal frequency, and the duty cycle are the parameters that need consideration when developing an effective jam code, but the effect of using different jammer waveforms is not generally known. Our study investigates the effect of using different jammer waveforms namely: the fixed carrier, low frequency, amplitude modulation (AM), and frequency-modulation jam codes, for jam signal analysis. Of the tested jam signals, it was found that the AM jam code is most effective in countering the conical-scan seeker due to the amplitude variations created by the jam signal.
The focal plane array in an MWIR camera should be configured optimally in terms of readout mode, stare time and gain setting to achieve the best (minimum) noise levels and/or maximal usable dynamic range under variable environmental conditions. In a long-range observation system noise is normally dominated by the environment, with optical contributions due to ambient illumination, target and background radiance, atmospheric transmission, path radiance, optics transmission and optics radiance. This optical signal is then detected according to the FPA spectral responsivity, which, combined with electronic contributors such as read noise, amplifier noise, clock noise, and quantization noise, eventually result in a digital output signal. A complete radiometric system modelling approach is used to predict the system NETD under a variety of representative environmental conditions and target ranges, which can then be used to inform decisions regarding the selection of the detector readout mode and gain mode, as well as setting the stare time for best operational performance. Results are presented demonstrating the effects of the various environmental factors and system parameters on NETD.
As pixel sizes reduce in the development of modern High Definition (HD) Mid Wave Infrared (MWIR) detectors the interpixel cross-talk becomes increasingly difficult to regulate. The diffusion lengths required to achieve the quantum efficiency and sensitivity of MWIR detectors are typically longer than the pixel pitch dimension, and the probability of inter-pixel cross-talk increases as the pixel pitch/diffusion length fraction decreases. Inter-pixel cross-talk is most conveniently quantified by the focal plane array sampling Modulation Transfer Function (MTF). Cross-talk MTF will reduce the ideal sinc square pixel MTF that is commonly used when modelling sensor performance. However, cross-talk MTF data is not always readily available from detector suppliers, and since the origins of inter-pixel cross-talk are uniquely device and manufacturing process specific, no generic MTF models appear to satisfy the needs of the sensor designers and analysts. In this paper cross-talk MTF data has been collected from recent publications and the development for a generic cross-talk MTF model to fit this data is investigated. The resulting cross-talk MTF model is then included in a MWIR sensor model and the impact on sensor performance is evaluated in terms of the National Imagery Interoperability Rating Scale’s (NIIRS) General Image Quality Equation (GIQE) metric for a range of fnumber/ detector pitch Fλ/d configurations and operating environments. By applying non-linear boost transfer functions in the signal processing chain, the contrast losses due to cross-talk may be compensated for. Boost transfer functions, however, also reduce the signal to noise ratio of the sensor. In this paper boost function limits are investigated and included in the sensor performance assessments.
A comprehensive model for staring array simulation is described. The model covers all effects from photon signal generation through to detection and processing in the staring array sensor. The model follows the signal flow from photon generation, through a staring focal plane array (FPA) from the detector, through several conversions in the read out integrated circuit (ROIC) and finally conversion to a digital signal. Spatial nonuniformity modeling for photoresponse, dark current generation and source follower offset is included. The list of noise sources includes: photon noise, quantum conversion uncertainty, dark noise, kTC noise, source follower noise and quantization noise. Several components with (simplified) nonlinear responses are also modeled: sense node capacitance variation with charge, source follower nonlinearity and nonlinearity in the digital conversion. The code implementations take images as input, applying the various processes independently on individual pixels (e.g., shot noise) or on complete images (e.g., spatial nonuniformity). Some noise sources vary temporally across frames (shot, thermal, kTC) while other noise sources are fixed across frames (fixed pattern noises). The application of the model is demonstrated by tracing the signal path from source to sensor output, with intermediate results along the path. The model is implemented in Python (as part of the pyradi open source computational radiometry module) and in a C++ image simulation. The purpose with this work is to predict what the performance of a given sensor will be in terms of image appearance, given the devices specifications and key design parameters. The execution of this work lead to the important recommendation that nonuniformity correction for infrared sensors should be performed at well fill levels corresponding to the minimum and maximum in the scene, not to fixed percentage levels in the charge well.
The objective with this work is to provide a `generic' model that can be adapted by adjusting model parameters. For more accurate modeling of specific sensors, dedicated models should be developed, but for all but the most demanding requirement, this model should be adequate in scope of detail and freedom of characteristics.
Aerosol attenuation in the atmosphere has a relatively weak spectral variation compared to molecular absorption. However, the solar spectral irradiance differs considerably for the sun at high zenith angles versus the sun at low zenith angles. The perceived color of a sunlit object depends on the object's spectral reflectivity as well as the irradiance spectrum. The color coordinates of the sunlit object, hence also the color balance in a scene, shift with changes in the solar zenith angle. The work reported here does not claim accurate color measurement. With proper calibration mobile phones may provide reasonably accurate color measurement, but the mobile phones used for taking these pictures and videos are not scientific instruments and were not calibrated. The focus here is on the relative shift of the observed colors, rather than absolute color. The work in this paper entails the theoretical analysis of color coordinates of surfaces and how they change for different colored surfaces. Then follows three separate investigations: (1) Analysis of a number of detailed atmospheric radiative transfer code (Modtran) runs to show from the theory how color coordinates should change. (2) Analysis of a still image showing how the colors of two sample surfaces vary between sunlit and shaded areas. (3) Time lapse video recordings showing how the color coordinates of a few surfaces change as a function of time of day. Both the theoretical and experimental work shows distinct shifts in color as function of atmospheric conditions. The Modtran simulations demonstrate the effect from clear atmospheric conditions (no aerosol) to low visibility conditions (5 km visibility). Even under moderate atmospheric conditions the effect was surprisingly large. The experimental work indicated significant shifts during the diurnal cycle.
Detailed radiometric analysis has shown that 3-5 µm medium wave infrared (MWIR) staring array well fill quickly reaches very high percentages, once hot optics, path radiance and inefficient f-number matching are taken into account. Well fill values of 90% plus are not unheard of. Likewise, the sensor noise eats away at the sensitivity. Therefore, it would appear that the very small signals often sought might not get sufficient dynamic bit-range to describe small signal flux propagating through poor atmospheres. This work presents a very detailed real-world model that includes all known factors that might compete for the bit resolution in a digitized sensor signal. The effect of different scene temperatures, atmospheric conditions and sensor design characteristics are briefly investigated. The effect of the various well fill contributors are shown in relation to each other in order to build an understanding of the nature of the total well fill. Finally, some mitigation measures are described to limit the negative effects of undue large well fill.
Hyperspectral Infrared (IR) signature measurements are performed in military applications including aircraft- and –naval vessel stealth characterization, detection/lock-on ranges, and flares efficiency characterization. Numerous military applications require high precision measurement of infrared signature characterization. For instance, Infrared Countermeasure (IRCM) systems and Infrared Counter-Countermeasure (IRCCM) system are continuously evolving. Infrared flares defeated IR guided seekers, IR flares became defeated by intelligent IR guided seekers and Jammers defeated the intelligent IR guided seekers .
A precise knowledge of the target infrared signature phenomenology is crucial for the development and improvement of countermeasure and counter-countermeasure systems and so precise quantification of the infrared energy emitted from the targets requires accurate spectral signature measurements. Errors in infrared characterization measurements can lead to weakness in the safety of the countermeasure system and errors in the determination of detection/lock-on range of an aircraft. The infrared signatures are analyzed, modeled, and simulated to provide a good understanding of the signature phenomenology to improve the IRCM and IRCCM technologies efficiency [7,8,9]. There is a growing need for infrared spectral signature measurement technology in order to further improve and validate infrared-based models and simulations.
The addition of imagery to Spectroradiometers is improving the measurement capability of complex targets and scenes because all elements in the scene can now be measured simultaneously. However, the limited dynamic range of the Focal Plane Array (FPA) sensors used in these instruments confines the ranges of measurable radiance intensities. This ultimately affects the radiometric accuracy of these complex signatures. We will describe and demonstrate how the ABB hyperspectral imaging spectroradiometer features enhanced the radiometric accuracy of spectral signature measurements of infrared military targets.
The quality, availability and diversity of satellite-derived earth observation data products are continuously improving. Such satellite products can provide an extensive and complementary view on many matters with respect to intensive but localised in-situ or ground measurements. A search has been undertaken on the available types and sources of satellite data products that could be applicable in the study of the spatio-temporal distribution of aero-optical turbulence in the atmospheric boundary layer. This has included all satellite data products that are relevant to the surface energy balance such as surface reflectance, temperature and emissivity. It was also important to identify active archive data services that can provide preprocessed and quality-filtered time-series products. Products derived from the Moderate Resolution Imaging Spectrometer (MODIS) and other sensors on the NASA Terra and Aqua platforms were of special interest. The use of climatological shortwave and longwave radiative transfer models, combined with satellite-derived data was explored as a method of elucidating the surface heat balance. An in-situ dataset from the Rietvlei vertical turbulence profiling campaign of 2013 was used to validate a number of aspects of the satellite-derived heat balance approach.
Infrared missiles pose a significant threat to civilian and military aviation. ManPADS missiles are especially
dangerous in the hands of rogue and undisciplined forces. Yet, not all the launched missiles hit their targets;
the miss being either attributable to misuse of the weapon or to missile performance restrictions. This paper
analyses some of the factors affecting aircraft vulnerability and demonstrates a structured analysis of the risk
and aircraft vulnerability problem.
The aircraft-missile engagement is a complex series of events, many of which are only partially understood.
Aircraft and missile designers focus on the optimal design and performance of their respective systems, often
testing only in a limited set of scenarios. Most missiles react to the contrast intensity, but the variability of the
background is rarely considered. Finally, the vulnerability of the aircraft depends jointly on the missile’s performance
and the doctrine governing the missile’s launch. These factors are considered in a holistic investigation.
The view direction, altitude, time of day, sun position, latitude/longitude and terrain determine the background
against which the aircraft is observed. Especially high gradients in sky radiance occur around the sun
and on the horizon. This paper considers uncluttered background scenes (uniform terrain and clear sky) and
presents examples of background radiance at all view angles across a sphere around the sensor.
A detailed geometrical and spatially distributed radiometric model is used to model the aircraft. This
model provides the signature at all possible view angles across the sphere around the aircraft. The signature is
determined in absolute terms (no background) and in contrast terms (with background). It is shown that the
background significantly affects the contrast signature as observed by the missile sensor. A simplified missile
model is constructed by defining the thrust and mass profiles, maximum seeker tracking rate, maximum guidance
acceleration and seeker sensitivity. For the purpose of this investigation the aircraft is equipped with conventional
pyrotechnic decoy flares and the missile has no counter-countermeasure means (security restrictions on open
publication). This complete simulation is used to calculate the missile miss distance, when the missile is launched
from different locations around the aircraft. The miss distance data is then graphically presented showing miss
distance (aircraft vulnerability) as a function of launch direction and range.
The aircraft vulnerability graph accounts for aircraft and missile characteristics, but does not account for
missile deployment doctrine. A Bayesian network is constructed to fuse the doctrinal rules with the aircraft
vulnerability data. The Bayesian network now provides the capability to evaluate the combined risk of missile
launch and aircraft vulnerability.
It is shown in this paper that it is indeed possible to predict the aircraft vulnerability to missile attack in a
comprehensive modelling and a holistic process. By using the appropriate real-world models, this approach is
used to evaluate the effectiveness of specific countermeasure techniques against specific missile threats. The use
of a Bayesian network provides the means to fuse simulated performance data with more abstract doctrinal rules
to provide a realistic assessment of the aircraft vulnerability.
The field of radiometry can be dangerous territory to the uninitiated, faced with the risk of errors and pitfalls. The concepts and tools explored in this book empower readers to comprehensively analyze, design, and optimize real-world systems. This book builds on the foundation of solid theoretical understanding, and strives to provide insight into hidden subtleties in radiometric analysis. Atmospheric effects provide opportunity for a particularly rich set of intriguing observations.
The term 'radiometry' is used in its wider context to specifically cover the calculation of flux. This wider definition is commonly used by practitioners in the field to cover all forms of manipulation, including creation, measurement, calculation, modeling, and simulation of optical flux.
Two concurrent themes frame the discussion: fragmenting a complex problem into simple building blocks and then designing complex systems from smaller elements. Analysis and design, as a creative synthesis of something new, cannot be easily taught other than by example; for this purpose, several case studies are presented. This book also provides a number of problems, some with solutions demonstrated in Matlab® and the Python™ pyradi toolkit.
Aircraft self-protection against heat seeking missile threats is an extremely important topic worldwide, recently even more so with the instability in the Middle East region due to, for example, the large number of man-portable air defense systems (MANPADS) that were stolen from army arsenals. A fundamental step in successfully achieving self-protection is the ability to capture and identify aircraft infrared signatures. This work discusses some of our efforts and results in creating an asset database for infrared signatures. The database was designed in a way that will feed an image processing engine to allow for automated feature and signature extraction. A common failing in the handling of target signature raw data is the fact that raw data files can become unreadable because of changes in technology, software applications or weak media archiving technology (e.g. corrupt DVD media). A second shortcoming is often the fact that large volumes of raw or processed data are stored in an unstructured manner, resulting in poor recall later. A third requirement is the portability of data between various processing software packages, legacy, current and future. This paper demonstrates how the challenge of future-proofing measured data is met with reference to the archiving and analysis of data from a recent measurement campaign. Recommendations for future work are given, based on the experience gained.
Electro-optical system design, data analysis and modeling involve a significant amount of calculation and processing. Many of these calculations are of a repetitive and general nature, suitable for including in a generic toolkit. The availability of such a toolkit facilitates and increases productivity during subsequent tool development: “develop once and use many times”. The concept of an extendible toolkit lends itself naturally to the open-source philosophy, where the toolkit user-base develops the capability cooperatively, for mutual benefit. This paper covers the underlying philosophy to the toolkit development, brief descriptions and examples of the various tools and an overview of the electro-optical toolkit.
The toolkit is an extendable, integrated collection of basic functions, code modules, documentation, example templates, tests and resources, that can be applied towards diverse calculations in the electro-optics domain. The toolkit covers (1) models of physical concepts (e.g. Planck’s Law), (2) mathematical operations (e.g. spectral integrals, spatial integrals, convolution, 3-D noise calculation), (3) data manipulation (e.g. file input/output, interpolation, normalisation), and (4) graphical visualisation (2-D and 3-D graphs).
Toolkits are often written in scriptable languages, such as Python and Matlab. This specific toolkit is implemented in Python and its associated modules Numpy, SciPy, Matlplotlib, Mayavi, and PyQt/PySide. In recent years these tools have stabilized and matured sufficiently to support mainstream tool development. Collectively, these tools provide a very powerful capability, even beyond the confines of this toolkit alone. Furthermore, these tools are freely available.
Rudimentary radiometric theory is given in the paper to support the examples given. Examples of the toolkit use, as described in the paper, include (1) spectral radiometric calculations of arbitrary source-medium-sensor configurations, (2) spectral convolution processing, (3) 3-D noise analysis, (4) loading of ASCII text files, binary files, Modtran tape7 and FLIR Inc *.ptw files, (5) data visualization in 2-D and 3-D graphs and plots, (6) detector modeling from detail design parameters (bulk material detectors), (7) color coordinate calculations, and (8) various utility functions.
The toolkit is developed as a cooperative effort between the CSIR, Denel SOC and DCTA. The project, available on Google Code at http://code.google.com/p/pyradi, is managed in accordance with general practice in the open source community.
The proliferation of a diversity of capable ManPADS missiles poses a serious threat to civil and military aviation.
Aircraft self protection against missiles requires increased sophistication as missile capabilities increase. Recent
advances in self protection include the use of directed infrared countermeasures (DIRCM), employing high power
lamps or lasers as sources of infrared energy. The larger aircraft self-protection scenario, comprising the missile,
aircraft and DIRCM hardware is a complex system. In this system, each component presents major technological
challenges in itself, but the interaction and aggregate behaviour of the systems also present design difficulties
and performance constraints. This paper presents a description of a simulation system, that provides the ability to model the individual components in detail, but also accurately models the interaction between the components, including the play out of the engagement scenario. Objects such as aircraft, flares and missiles are modelled as a three-dimensional object with a physical body, radiometric signature properties and six-degrees-of-freedom kinematic behaviour. The object’s physical body is modelled as a convex hull of polygons, each with radiometric properties. The radiometric properties cover the 0.4–14 μm spectral range (wider than required in current technology missiles) and include reflection of sunlight, sky radiance, atmospheric effects as well thermal self-emission. The signature modelling includes accurate temporal variation and spectral descriptions of the object’s signature. The object’s kinematic behaviour is modelled using finite difference equations. The objects in the scenario are placed and appropriately orientated in a three-dimensional world, and the engagement is allowed to play out. Low-power countermeasure techniques against the missile seekers include jamming (decoying by injecting false signals) and dazzling (blinding the sensor). Both approaches require knowledge of the missile sensor and/or signal processing hardware. Simulation of jamming operation is achieved by implementing the missile-specific signal processing in the simulation (i.e. accurate white-box modelling of actual behaviour). Simulation of dazzling operation is more difficult and a parametric black-box modelling approach is taken. The design and calibration of the black-box dazzling behaviour is done by heuristic modelling based on experimental observations. The black-box behaviour can later be replaced with verified behaviour, as obtained by experimental laboratory and field work, using the specified missile hardware. The task of simulating a DIRCM system is scoped, by considering the threats, operational requirements and detailed requirements of the respective models. A description is given of the object models in the simulation, including key performance parameters of the models and a brief description of how these are implemented. The paper closes with recommendations for future research and simulation investigations.
The development of modern imaging and non-imaging infrared missile signal processing and countermeasure techniques strongly relies on high quality simulated imagery of target and countermeasure signatures. Likewise, the development of an effective countermeasure technique or system for aircraft self-protection requires accurate missile behaviour modelling. The development of these algorithms and protocols can be done most effectively in an accurate infrared imaging simulation. This paper investigates the requirements for such a simulation system, supporting the evaluation of the missile behaviour in the missile-aircraft engagement scenario. The development and evaluation of target detection and tracking algorithms, or countermeasure systems, requires a comprehensive simulation environment where thousands of missile flights can be simulated, covering a wide variety of scenarios and signature conditions. The missile seeker algorithms generally detect and classify targets based on intensity, spatial and dynamic characteristics. The key considerations identified for such an imaging infrared simulation system are: 1) radiometric accuracy in all spectral bands, i.e. sunlight and thermal radiance to provide correct colour ratios; 2) accurate emitting source surface temperature behaviour, be it by aerodynamic or thermodynamic heating; 3) high fidelity geo- metrical and spatial texture modelling to provide shape of targets and countermeasures; 4) true dynamics and kinematic behaviour in six degrees of freedom; 5) detailed modelling of signatures and backgrounds; 6) accurate atmospheric transmittance and path radiance models; 7) realistic rendering of the scene image in radiometric, spatial and temporal terms; and 8) comprehensive sensor modelling to account for primary and second order imaging effects. This paper briefly analyses the broader framework of requirements for an imaging simulation system, in the 0.4 to 14 μm spectral bands. An existing imaging simulation system, OSSIM, is used to evaluate the identified key requirements for accurately simulating the missile-aircraft engagement scenario. Parameters considered include signature spectral colour ratio, spatial shape, kinematics, temporal behaviour, as well as the effect of the atmosphere and background. From this analysis the significance and relevance of the modelled signature elements are reviewed, thereby confirming the key requirements for simulating the missile-aircraft engagement.
The development and optimisation of modern infrared systems necessitates the use of simulation systems to create
radiometrically realistic representations (e.g. images) of infrared scenes. Such simulation systems are used in
signature prediction, the development of surveillance and missile sensors, signal/image processing algorithm
development and aircraft self-protection countermeasure system development and evaluation.
Even the most cursory investigation reveals a multitude of factors affecting the infrared signatures of realworld
objects. Factors such as spectral emissivity, spatial/volumetric radiance distribution, specular reflection,
reflected direct sunlight, reflected ambient light, atmospheric degradation and more, all affect the presentation of
an object's instantaneous signature. The signature is furthermore dynamically varying as a result of internal and
external influences on the object, resulting from the heat balance comprising insolation, internal heat sources,
aerodynamic heating (airborne objects), conduction, convection and radiation. In order to accurately render the
object's signature in a computer simulation, the rendering equations must therefore account for all the elements
of the signature.
In this overview paper, the signature models, rendering equations and application frameworks of three infrared
simulation systems are reviewed and compared. The paper first considers the problem of infrared scene simulation
in a framework for simulation validation. This approach provides concise definitions and a convenient context for
considering signature models and subsequent computer implementation. The primary radiometric requirements
for an infrared scene simulator are presented next.
The signature models and rendering equations implemented in OSMOSIS (Belgian Royal Military Academy),
DIRSIG (Rochester Institute of Technology) and OSSIM (CSIR & Denel Dynamics) are reviewed. In spite
of these three simulation systems' different application focus areas, their underlying physics-based approach is
similar. The commonalities and differences between the different systems are investigated, in the context of their
somewhat different application areas.
The application of an infrared scene simulation system towards the development of imaging missiles and
missile countermeasures are briefly described.
Flowing from the review of the available models and equations, recommendations are made to further enhance
and improve the signature models and rendering equations in infrared scene simulators.
The behaviour of a complex adaptive system (CAS) cannot be predicted from the behaviour of its constituent components. Individual components of the system interacts with each other such that the behaviour at the aggregate level is not predictable from knowledge about the components. Software agents based on the 'Belief-Desire-Intention' (BDI) paradigm are used to model the various roles and actors in a military complex adaptive system. Each agent can sense some aspects of its environment, interprets its sensory perceptions, and reacts in a manner consistent with its intended task or goal. The design of the system entails setting down the internal rules for each agent, as well as the rules of interaction between the agents. During the simulation run, the agents are allowed to interact according to their programmed rule sets, and the emergent behaviour of the system as a whole is observed. The application of complex adaptive system theory is used to model the interaction between elements of a military command and control system and information operations/warfare core areas. The purpose with the investigation is to investigate the optimal integration of activities between the various information operations core areas.
Thermal crossover is the phenomenon where the infrared signatures of two different objects in a scene are indistinguishable. A prediction method was developed where a series of infrared images is used as the basis to predict thermal crossover under different climatic conditions. Image recordings are made over the full diurnal cycle, for a fixed scene. We then develop a theoretical thermal model, describing dynamic temporal behaviour. Using the recorded images, the model parameters required to describe the temporal behaviour of the observed scene, are determined. The model, with the appropriate model parameters, is then used to create a new image sequence, predicting the scene appearance under different climatic conditions. The new image sequence is used to predict thermal crossover under the new set of climatic conditions. The paper closes with conclusions and recommendations for future work.