7,672 research outputs found
Evaluation of a color fused dual-band NVG
No full textWe have tested a prototype dual-band NVG system consisting of two NVGs fitted with filters that split the NVG sensitive range into a short (visual) and a long wavelength (NIR) band. The Color-the-night technique (see Hogervorst & Toet, SPIE D&S ‘08) was used to fuse the images of the two sensors. We designed a color scheme especially optimized for the detection of camouflaged targets. The added value of this system was evaluated in an experiment in which observers had to detect targets (green and blue tubes). Daytime images were taken with a normal camera, and NVG images were recorded at night. Performance was tested for i) the visual band only, ii) the NIR-band only, iii) normal NVG, iv) daytime imagery and v) color fused dual-band NVG. The results show that some targets were detected in the individual bands, but most targets were detected in the dual-band system, with performance comparable to that of the band optimally presenting that particular target. Our evaluation shows the added value of dual-band over single band NVG for the detection of targets, and suggests better situational awareness and perceived depth
Toward realistic night-vision simulation
No full textA novel color-transformation method converts daytime scenes into night-vision goggle images suitable for realistic nighttime trainin
Method for applying daytime colors to nighttime imagery in realtime
No full textWe present a fast and efficient method to derive and apply natural colors to nighttime imagery from multiband sensors. The color mapping is derived from the combination of a multiband image and a corresponding natural color reference image. The mapping optimizes the match between the multiband image and the reference image, and yields a nightvision image with colors similar to that of the daytime image. The mapping procedure is simple and fast. Once it has been derived the color mapping can be deployed in realtime. Different color schemes can be used tailored to the environment and the application. The expectation is that by displaying nighttime imagery in natural colors human observers will be able to interpret the imagery better and faster, thereby improving situational awareness and reducing reaction times
Hyperspectral Data Analysis and Visualisation
No full textElectro-Optical (EO) imaging sensors are widely used for a range of tasks, e.g. for Target Acquisition (TA: detection, recognition and identification of (military) relevant objects) or visual search. These tasks can be performed by a human observer, by an algorithm (Automatic Target Recognition) or by both (Aided Target Recognition). In the past decades, the development of night vision devices in the thermal infrared and image intensifying systems has greatly extended the applicability of EO systems. Despite of these rapid developments, the current generation of sensors has important limitations. Until now, operational thermal imagers are sensitive to IR (infrared) radiation from a single spectral band in the Long Wave (8-14 μm, LWIR) or Mid Wave (3-5 μm, MWIR) infrared region. These so-called broad band sensors basically produce a monochrome (i.e. a black-and-white pan-chromatic) image that deviates considerably from a normal daylight view, and is based on temperature contrasts in a scene. With these systems, the distinction between real targets and decoys, r between military and civilian targets is often difficult to make. Also, camouflaged targets or targets hat are hidden deep in the woods are difficult to detect. Recognizing different objects and materials may be difficult. Examples of misinterpretations when using an Image Intensifier system are grass that looks like snow, or trees that look like bushes, when seen from a helicopter. These misinterpretations may lead to disorientation (loss of Situational Awareness) or to a (fatal) wrong distance estimation. Currently, multi-band and hyperspectral imaging sensors in the thermal infrared are under development. Traditionally hyperspectral imagers were developed for satellites with applications ranging from monitoring the environment, climate analysis, detection of pollution and fires. These systems also promise significant improvements in military task performance. With these new systems, targets may be distinguished not only on the basis of differences in radiation magnitude, but also on differences in spectral properties
Colour-the-INSight : Combining a direct view rifle sight with fused intensified and thermal imagery
No full textWe present the design and evaluation of a new demonstrator rifle sight viewing system containing direct view, red aim point and fusion of an (uncooled, LWIR) thermal sensor with a digital image intensifier. Our goal is to create a system that performs well under a wide variety of (weather) conditions during daytime and nighttime and combines the advantages of the various sensor systems. A real-time colour image with salient hot targets is obtained from the night vision sensors by implementing the Colour-the-Night fusion method (Hogervorst & Toet, 2010) on the on-board processor. The prototype system was evaluated in a series of field trials with military observers performing detection and identification tasks. The tests showed that during daytime the addition of a thermal image to direct vision is advantageous, e.g. for the detection of hot targets. At nighttime, the fusion of thermal and image intensified imagery results in increased situational awareness and improved detection of (hot) targets. For identification of small (handheld) objects, the technology needs to be further refined
On the relationship between human search strategies, conspicuity and search performance
No full textWe determined the relationship between search performance with a limited field of view (FOV) and several scanning- and scene parameters in human observer experiments. The observers (38 trained army scouts) searched through a large search sector for a target (a camouflaged person) on a heath. From trial to trial the target appeared at a different location. With a joystick the observers scanned through a panoramic image (displayed on a PC-monitor) while the scan path was registered. Four conditions were run differing in sensor type (visual or thermal infrared) and window size (large or small). In conditions with a small window size the zoom option could be used. Detection performance was highly dependent on zoom factor and deteriorated when scan speed increased beyond a threshold value. Moreover, the distribution of scan speeds scales with the threshold speed. This indicates that the observers are aware of their limitations and choose a (near) optimal search strategy. We found no correlation between the fraction of detected targets and overall search time for the individual observers, indicating that both are independent measures of individual search performance. Search performance (fraction detected, total search time, time in view for detection) was found to be strongly related to target conspicuity. Moreover, we found the same relationship between search performance and conspicuity for visual and thermal targets. This indicates that search performance can be predicted directly by conspicuity regardless of the sensor type. Keywords: Search performance, Field of Regard, Field of View, Modelling, Conspicuity, Scan path, Zooming, Detection time, Detection probability, Search strateg
Capturing the sampling effects : A TOD sensor performance model
No full textThe standard way to characterize sensor performance is by means of the Minimum Resolvable Temperature Difference (MRTD) and Minimum Resolvable Contrast (MRC) methods. These methods are based on Fourier analysis and work reasonably well for linear (analogue) systems. However, nonlinear effects, such as sampling, are not properly accounted for. As an alternative, the Triangle Orientation Discrimination (TOD) method has been proposed, based on 4 oriented triangles, that can handle nonlinear effects. Here, we present a model that predicts the TOD-sensor performance characterization curve from the system parameters. It consists of i) a sensor model and ii) a model of the visual system of the observer. The sensor model generates display images which are fed into the visual system model. The visual system is modeled by a bank of band-pass filters which mimic the pattern of neural activity in the visual cortex (using a common stack model). The neural activity is calculated and internal noise is added. Finally, a decision is made based on a correlation with the expected neural activity of the 4 possible inputs. The model has been validated with two human observer experiments in which the TOD-curve 1) of the naked eye, and 2) of a simulated thermal staring sensor system were measured. An internal noise level could be found for which the TOD of the naked eye of the two observers could be predicted. The model gives reasonable (but somewhat optimistic) predictions of the TOD-sensor performance curve of the simulated staring camera. Although more tests and modifications are required, these preliminary results suggest that the model can be developed into a model which predicts the TOD for all kinds of sensor systems, which may include sampling effects, noise, blur and (local) image enhancement methods
Identifiability : a fast way to measure for identification performance
No full textWe present a new measure called target identifiability, as an efficient alternative for measuring identification scores. Identifiability is operationally defined as the amount of blur required to reduce the target signature to its identification threshold. It can quickly be determined using a simple adjustment procedure. To validate the new measure, we measured the identifiability of targets in a set of real and simulated thermal images. The identification scores for these targets were available from a previous study. Our results show that identifiability indeed determines identification performance. Sufficient accuracy can be obtained with only a few (typically 2 or 3) trained observers. The associated measurement procedure is simple and requires only a limited amount of time
Deep anisotropic dry etching of silicon microstructures by high-density plasmas
No full textThis thesis deals with the dry etching of deep anisotropic microstructures in monocrystalline silicon by high-density plasmas. High aspect ratio trenches are necessary in the fabrication of sensitive inertial devices such as accellerometers and gyroscopes. The etching of silicon in fluorine-based plasmas is isotropic. To obtain anisotropy the addition of sidewall passivation is necessary. This is achieved with both oxygen passivation at low temperatures and fluorocarbon passivation at room temperature. A quantitative approach was pursued to explain the etching mechanism. The etch results were analysed using the measured plasma species fluxes and the surface composition. Moreover, the transport of the plasma species in narrow anisotropic structures is a fundamental factor determining the etch rate and the profile evolution. The experimental methods such as the etching equipment, plasma diagnostics, surface analysis and sample preparation are described in chapter 2. Three etching processes were investigated: the cryogenic etching process with oxygen passivation at low temperatures, the Bosch process with fluorocarbon passivation at room temperature and the novel triple pulse process that was developed in our laboratory. The polymer deposition mechanism and the characteristic role of the ions are also explained. The cryogenic etching process is discussed in chapter 3. Fluorine radicals, oxygen radicals and ion bombardment are responsible for the three main sub-processes, that is, etching, sidewall passivation and depassivation of the trench bottom, respectively. Etching experiments with an extremely low ion-to-radical flux ratio were used to reveal the etching mechanism. Crystal orientation dependent etching leading to Si(111) crystal facets is observed in a surface kinetics controlled regime. By varying the plasma conditions it is possible to adjust the etching mechanism from fluorine-limited to ion-limited. Controlled etching is obtained because the etching is tuned from aspect ratio dependent in the fluorine-limited domain to aspect ratio independent in the ion-limited domain. The transport of radicals in high aspect ratio trenches is an important limiting factor and was investigated with special structures. The etch results are described by an analytic model that is based on the surface site balance of fluorine and oxygen radicals. The results are further explained with a Monte Carlo simulation model. The Bosch process is clarified in chapter 4. The anisotropy of the etched structures is controlled by balancing the etching and passivation pulse. However, the maximal obtainable aspect ratio is limited by convergence of the trench sidewalls due to excessive passivation. The maximal obtainable aspect ratio increases if the ion-to-radical flux ratio increases. The transport of ions is an important limiting factor in the depassivation of the bottom of the trench. Divergence of the ion beam leads to a reduction of the ion flux, so that the fluorocarbon passivation is insufficiently removed near the base of the sidewalls. The average ion angle was measured and correlated to the maximal obtainable aspect ratio. The Bosch process was improved at the depassivation side with the triple pulse process and at the passivation side with preferential sidewall deposition. The triple pulse process that is described in chapter 5 has the aim to improve the depassivation in deep trenches. The three main sub-processes are decoupled using a separate depassivation pulse directly after the etching and passivation pulses. The fluorocarbon passivation is efficiently removed with low-pressure, high-density, oxygen-based plasmas. The investigated plasma chemistries include O2, CO2 and SO2. The triple pulse process leads to better profile control with a straight trench bottom. However, the maximal obtainable aspect ratio is comparable to the Bosch process because a larger etch depth and a small lateral etch cancel out. The polymer deposition mechanism is treated in chapter 6 with the aim to understand the fluorocarbon passivation in deep trenches. The deposition on plane surfaces and on special structures was investigated to distinguish between the radical-induced and ion-enhanced components. A simple analytical model, which explains the main deposition characteristics, was developed. Preferential sidewall deposition is obtained for higher ion fluxes and higher bias voltages where sputtering plays an important role. In this case no fluorocarbon passivation has to be removed from the bottom of the trench. The trench profile was optimised in the Bosch process by tuning the bias voltage during etching and passivation independently. It resulted in perfectly anisotropic trenches but the maximal obtainable aspect ratio was still limited by a small lateral etch. The characteristic role of the ions in the etching mechanism is explained in chapter 7. Ion-induced etching of both SiC in a SF6-O2 plasma and Si in a Cl2 plasma were investigated. The impact of the ions on the profile evolution can be examined more explicitly because spontaneous chemical reactions are absent for these plasma-material systems. The etching mechanism varies from fluorine-limited to ion-limited depending on the radical-to-ion flux ratio. Microtrenches are observed for an ion-limited etching mechanism. Fluorine-limited SiC etching is aspect ratio dependent in contrast to ion-limited SiC etching, which is aspect ratio independent. The etching of high aspect ratio SiC structures is limited by the positive sidewall taper. This is presumably caused by insufficient removal of the thin fluorocarbon layer on the surface. Si etching in a Cl2 plasma is always aspect ratio independent in contrast to SiC etching because of the low reaction probability. The conclusions and recommendations of this thesis are given in chapter 8.Applied Science
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