Mariusz Kastek

Method of detectors offset correction in thermovision camera with uncooled microbolometric focal plane array

A microbolometer is an uncooled thermal sensor of infra-red radiation. In thermal imaging, microbolometers organized in arrays called focal plane arrays (FPA) are used. Because of technological process microbolometric FPAs features unwanted detector gain and offset nonuniformity. Because of that, the detector matrix, being exposed to uniform infrared radiation produces nonuniform image with superimposed fixed pattern noise (FPN). To eliminate FPN, nonuniformity correction (NUC) algorithms are used. The offset of detector in array depends from mean temperature of FPA. Every single detector in matrix has its temperature drift, so the characteristic of every detector changes over temperature. To overpass this problem, a temperature stabilization of FPA is commonly used, however temperature stabilization is a relatively power demanding process. In this article a method of offset calculation and correction for every detector in array in function of mean array temperature is described. The method of offset temperature characteristic estimation is shown. The elaborated method let to use unstabilized microbolometric focal plane array in thermographic camera. Method of offset correction was evaluated for amorphous silicon based UL 03 04 1 detector array form ULIS.

Sniper detection using infrared camera: technical possibilities and limitations

The paper discusses technical possibilities to build an effective system for sniper detection using infrared cameras. Descriptions of phenomena which make it possible to detect sniper activities in infrared spectra as well as analysis of physical limitations were performed. Cooled and uncooled detectors were considered. Three phases of sniper activities were taken into consideration: before, during and after the shot. On the basis of experimental data the parameters defining the target were determined which are essential in assessing the capability of infrared camera to detect sniper activity. A sniper body and muzzle flash were analyzed as targets. The simulation of detection ranges was done for the assumed scenario of sniper detection task. The infrared sniper detection system was discussed, capable of fulfilling the requirements. The discussion of the results of analysis and simulations was finally presented.

The calibration stand for thermal camera module with infrared focal plane array

In areas like military systems, surveillance systems, or industrial process control, more and more often there is a need to operate in limited visibility conditions or even in complete darkness. In such conditions vision systems can benefit by using thermal vision cameras. In thermal imaging an infrared radiation detector arrays are used. Contemporary infrared detector arrays suffers from technological imprecision which causes that the response to uniform radiation results in nonuniform image with superimposed fixed pattern noise (FPN). In order to compensate this noise there is a need to evaluate detectors characteristics like responsivity and offset of every detector in array. Some of the detectors in cooled detector arrays can be also defective. Signal from defective pixels has to be in such system replaced. In order to replace defective pixels, there is a need to detect them. Identification of so-called blinking pixels needs long time measurement, which in designed calibration stand is also possible. The paper presents the design of infrared detector array measurement stand allowing measurement of mentioned parameters. Measurement stand was also used to evaluate temporal noise of infrared detection modules. In article there is a description of optical system design and parameters of used reference blackbodies. To capture images from camera modules a specially designed digital image interface was used. Measurement control and calculations were made in specially written IRDiag software. Stand was used to measure parameters for cameras based on cooled focal plane arrays from Sofradir. Results of two-point nonuniformity correction are also presented.

Adaptable infrared image processing module implemented in FPGA

Rapid development of infrared detector arrays caused a need to develop robust signal processing chain able to perform operations on infrared image in real-time. Every infrared detector array suffers from so-called nonuniformity, which has to be digitally compensated by the internal circuits of the camera. Digital circuit also has to detect and replace signal from damaged detectors. At the end the image has to be prepared for display on external display unit. For the best comfort of viewing the delay between registering the infrared image and displaying it should be as short as possible. That is why the image processing has to be done with minimum latency. This demand enforces to use special processing techniques like pipelining and parallel processing. Designed infrared processing module is able to perform standard operations on infrared image with very low latency. Additionally modular design and defined data bus allows easy expansion of the signal processing chain. Presented image processing module was used in two camera designs based on uncooled microbolometric detector array form ULIS and cooled photon detector from Sofradir. The image processing module was implemented in FPGA structure and worked with external ARM processor for control and coprocessing. The paper describes the design of the processing unit, results of image processing, and parameters of module like power consumption and hardware utilization.

Multispectral and hyperspectral measurements of soldier's camouflage equipment

In todays electro-optic warfare era, it is more than vital for one nations defense to possess the most advanced measurement and signature intelligence (MASINT) capabilities. This is critical to gain a strategic advantage in the planning of the military operations and deployments. The thermal infrared region of the electromagnetic spectrum is a key region that is exploited for infrared reconnaissance and surveillance missions. The Military University of Technology has conducted an intensive measurement campaign of various soldiers camouflage devices in the scope of building a database of infrared signatures. One of todays key technologies required to perform signature measurements has become infrared hyperspectral and broadband/multispectral imaging sensors. The Telops Hyper-Cam LW product represents a unique commercial offering with outstanding performances and versatility for the collection of hyperspectral infrared images. The Hyper-Cam allows for the infrared imagery of a target (320 × 256 pixels) at a very high spectral resolution (down to 0.25 cm-1). Moreover, the Military University of Technology has made use of a suite of scientific grade commercial infrared cameras to further measure and assess the targets from a broadband/multispectral perspective. The experiment concept and measurement results are presented in this paper.

Digital image processing in high resolution infrared camera with use of programmable logic device

In article a digital system for high resolution infrared camera control and image processing is described. The camera is built with use of bolometric focal plane array of size 640 by 480 detectors. Single detector in array has size of 25 μm and can detect incident radiation from the spectral range of 8÷12 μm thanks to the special filter installed in specially designed entrance window. The most important tasks of infrared image processing system are array readout and correction of detectors offset and responsivity variations. The next tasks of the system are conversion of analog voltage signals from microbolometers in array to digital form and then composition of a thermal image. Microbolometer array needs to be controlled via several signals. The signal generator for readout circuit is capable of changing various timing parameters like frame rate or integration time of the detector array. The changes in these parameters can be done via special set of memory mapped registers. The infrared data received from detector array is transferred via data bus to modules performing image processing, for example techniques for image enhancement. Image processing algorithms necessary for infrared image generation are nonuniformity correction, bad pixel replacement and radiometric calibration. Optionally an additional image processing techniques can be performed like edge enhancement, dynamic range compression or object identification. The elaborated architecture of the system allowed easy change of parameters of the system and to adopt many new algorithms without significant hardware changes. Scientific work funded from science fund for years 2009-2011 as a development project.

Multispectral system for perimeter protection of stationary and moving objects

Introduction of a ground multispectral detection has changed organization and construction of perimeter security systems. The perimeter systems with linear zone sensors and cables have been replaced with a point arrangement of sensors with multispectral detection. Such multispectral sensors generally consist of an active ground radar, which scans the protected area with microwaves or millimeter waves, a thermal camera, which detects temperature contrast and a visible range camera. Connection of these three different technologies into one system requires methodology for selection of technical conditions of installation and parameters of sensors. This procedure enables us to construct a system with correlated range, resolution, field of view and object identification. The second technical problem connected with the multispectral system is its software, which helps couple the radar with the cameras. This software can be used for automatic focusing of cameras, automatic guiding cameras to an object detected by the radar, tracking of the object and localization of the object on the digital map as well as identification and alarming. In this paper two essential issues connected with multispectral system are described. We focus on methodology of selection of sensors parameters. We present usage of a spider-chart, which was adopted to the proposed methodology. Next, we describe methodology of automation of the system regarding an object detection, tracking, identification, localization and alarming.

Comparative Studies of Passive Imaging in Terahertz and Mid-Wavelength Infrared Ranges for Object Detection

We compared the possibility of detecting hidden objects covered with various types of clothing by using passive imagers operating in a terahertz (THz) range at 1.2 mm (250 GHz) and a mid-wavelength infrared at 3-6 μm (50-100 THz). We investigated theoretical limitations, performance of imagers, and physical properties of fabrics in both the regions. In order to investigate the time stability of detection, we performed measurements in sessions each lasting 30 min. We present a theoretical comparison of two spectra, as well as the results of experiments. In order to compare the capabilities of passive imaging of hidden objects, we combined the properties of textiles, performance of imagers, and properties of radiation in both spectral ranges. The paper presents the comparison of the original results of measurement sessions for the two spectrums with analysis.

Construction, parameters, and research results of thermal weapon sight

The paper presents the thermal sight for small arms weapons, which can be classified as 3rd gen thermal camera. The sight operates in LWIR (long wave infrared) spectra band and utilizes uncooled microbolometer focal plane array (FPA) with stabilized temperature (by means of Peltier module). The assumed technical and tactical characteristics of the presented sight were confirmed during laboratory test (including climate and vibration tests). The sight was also tested during field trials conducted at Military Institute of Armament Technology, where it was mounted on seven different weapon types with calibers from 5.56 to 12.7 mm.

Method of gas detection applied to infrared hyperspectral sensor

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP