Cornelius J. Willers

Non-uniformity correction and bad pixel replacement on LWIR and MWIR images

To fully exploit the potential of current generation infrared focal plane arrays, it is crucial to correct for the fixed pattern noise. This paper presents two-point non-uniformity corrections (NUC) applied to infrared images acquired with long wave and medium wave infrared cameras. Pixels that are not corrected by the NUC process, defined as bad pixels, were identified and replaced using a nearest neighbor algorithm.

Specializing CRISP-DM for evidence mining

Forensic analysis requires a keen detective mind, but the human mind has neither the ability nor the time to process the millions of bytes on a typical computer hard disk. Digital forensic investigators need powerful tools that can automate many of the analysis tasks that are currently being performed manually.

Key considerations in infrared simulations of the missile-aircraft engagement

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.

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

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.

Exploration of satellite-derived data products for atmospheric turbulence studies

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.

Future-proofing an aircraft self-protection IR signature database

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.

Confidence estimation in the application of simulation in the development of aircraft self-protection measures

This paper describes the application of simulation in the development of aircraft self-protection countermeasures against infrared missiles. The integrated approach followed here consists of repeated cycles of materiel1 characterisation, analysis and modelling, design synthesis, solution implementation and deployment. Results from the activities in this workflow are used to support the estimation of confidence in the simulation tools. The well known Qualification, Verification and Validation (QVV) model is extended by adding the notion of quality of scenario information to the physical characterisation, the conceptual modelling and the computer modelling of system elements. It is shown that a simulation with high confidence requires extensive validation testing. Some measure of confidence can be achieved by ensuring that the conceptual and computer models support extrapolation between fewer validated ‘islands’. To express simulation confidence, a ‘potential field’ is proposed; the value of this potential is determined by the degree to which the QVV requirements are met. The results from an infrared simulation model is used to demonstrate this principle.

Small pixel cross-talk MTF and its impact on MWIR sensor performance

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.

Aircraft vulnerability analysis by modeling and simulation

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.

Simulating the DIRCM engagement: component and system level performance

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.