Ms. Maria S. Willers Profile

Maria S. Willers

IR Modelling & Simulation Specialist at Denel Dynamics

SPIE Involvement:

Author

Proceedings Article | 3 February 2017 Paper

Staring array sensor model for simulation implementation

Cornelius Willers, Maria Willers

Proceedings Volume 10036, 100360S (2017) https://doi.org/10.1117/12.2244780

KEYWORDS: Sensors, Staring arrays, Signal detection, Interference (communication), Electrons, Capacitance, Charge-coupled devices, Capacitors, Electro optical modeling, CMOS sensors

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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.

Proceedings Article | 7 October 2014 Paper

Aircraft vulnerability analysis by modeling and simulation

Cornelius Willers, Maria Willers, Alta de Waal

Proceedings Volume 9251, 92510M (2014) https://doi.org/10.1117/12.2073751

KEYWORDS: Missiles, Sun, Sensors, Environmental sensing, Atmospheric sensing, Modeling, Transmittance, Infrared radiation, Atmospheric modeling, Optical spheres

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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.

Proceedings Article | 8 November 2012 Paper

Pyradi: an open-source toolkit for infrared calculation and data processing

Cornelius Willers, Maria Willers, Ricardo Augusto Santos, Petrus van der Merwe, Johannes Calitz, Alta de Waal, Azwitamisi Mudau

Proceedings Volume 8543, 85430J (2012) https://doi.org/10.1117/12.976043

KEYWORDS: Sensors, Optical filters, 3D modeling, Visualization, Transmittance, MATLAB, Convolution, Infrared radiation, Electro optics, Forward looking infrared

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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.

Proceedings Article | 8 November 2012 Paper

Simulating the DIRCM engagement: component and system level performance

Cornelius Willers, Maria Willers

Proceedings Volume 8543, 85430M (2012) https://doi.org/10.1117/12.974812

KEYWORDS: Missiles, Sensors, Directed infrared countermeasures, Modeling, 3D modeling, Signal processing, Systems modeling, Image sensors, Laser countermeasures, Kinematics

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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.

Proceedings Article | 8 November 2012 Paper

Key considerations in infrared simulations of the missile-aircraft engagement

Maria Willers, Cornelius Willers

Proceedings Volume 8543, 85430N (2012) https://doi.org/10.1117/12.974801

KEYWORDS: Missiles, Sensors, Modeling, Infrared radiation, Image sensors, Image processing, Infrared imaging, Algorithm development, Imaging systems, Transmittance

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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.

Proceedings Article | 7 October 2011 Paper

Signature modelling and radiometric rendering equations in infrared scene simulation systems

Cornelius Willers, Maria Willers, Fabian Lapierre

Proceedings Volume 8187, 81870R (2011) https://doi.org/10.1117/12.903352

KEYWORDS: Sensors, Missiles, Infrared radiation, Computer simulations, Algorithm development, Thermal modeling, Infrared imaging, Infrared signatures, Signal processing, Systems modeling

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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.

Showing 5 of 6 publications

Conference Committee Involvement (5)

Technologies for Optical Countermeasures

27 September 2016 | Edinburgh, United Kingdom

Technologies for Optical Countermeasures

23 September 2015 | Toulouse, France

Technologies for Optical Countermeasures

24 September 2014 | Amsterdam, Netherlands

Technologies for Optical Countermeasures X

25 September 2013 | Dresden, Germany

Technologies for Optical Countermeasures

26 September 2012 | Edinburgh, United Kingdom

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