Improving the surveillance capacity over wide zones requires a set of smart battery-powered Unattended Ground Sensors capable of issuing an alarm to a decision-making center. Only high-level information has to be sent when a relevant suspicious situation occurs. In this paper we propose an innovative bio-inspired approach that mimics the human bi-modal vision mechanism and the parallel processing ability of the human brain. The designed prototype exploits two levels of analysis: a low-level panoramic motion analysis, the peripheral vision, and a high-level event-focused analysis, the foveal vision. By tracking moving objects and fusing multiple criteria (size, speed, trajectory, etc.), the peripheral vision module acts as a fast relevant event detector. The foveal vision module focuses on the detected events to extract more detailed features (texture, color, shape, etc.) in order to improve the recognition efficiency. The implemented recognition core is able to acquire human knowledge and to classify in real-time a huge amount of heterogeneous data thanks to its natively parallel hardware structure. This UGS prototype validates our system approach under laboratory tests. The peripheral analysis module demonstrates a low false alarm rate whereas the foveal vision correctly focuses on the detected events. A parallel FPGA implementation of the recognition core succeeds in fulfilling the embedded application requirements. These results are paving the way of future reconfigurable virtual field agents. By locally processing the data and sending only high-level information, their energy requirements and electromagnetic signature are optimized. Moreover, the embedded Artificial Intelligence core enables these bio-inspired systems to recognize and learn new significant events. By duplicating human expertise in potentially hazardous places, our miniature visual event detector will allow early warning and contribute to better human decision making.
Pedestrian movement along critical infrastructures like pipes, railways or highways, is of major interest in surveillance applications as well as its behavior in urban environment. The goal is to anticipate illicit or dangerous human activities. For this purpose, we propose an all-in-one small autonomous system which delivers high level statistics and reports alerts in specific cases. This situational awareness project leads us to manage efficiently the scene by performing movement analysis. A dynamic background extraction algorithm is developed to reach the degree of robustness against natural and urban environment perturbations and also to match the embedded implementation constraints. When changes are detected in the scene, specific patterns are applied to detect and highlight relevant movements. Depending on the applications, specific descriptors can be extracted and fused in order to reach a high level of interpretation. In this paper, our approach is applied to two operational use cases: pedestrian urban statistics and railway surveillance. In the first case, a grid of prototypes is deployed over a city centre to collect pedestrian movement statistics up to a macroscopic level of analysis. The results demonstrate the relevance of the delivered information; in particular, the flow density map highlights pedestrian preferential paths along the streets. In the second case, one prototype is set next to high speed train tracks to secure the area. The results exhibit a low false alarm rate and assess our approach of a large sensor network for delivering a precise operational picture without overwhelming a supervisor.
Range-gated active imaging systems are more and more used for surveillance and night vision applications. Their ability
to improve vision through fog, snow or rain makes them good candidates to be used for automotive safety. But even if
they increase safety, expensive options have no chances to come out from the laboratory and to be integrated in a car.
Instead of using a complete active imaging system, i.e. a laser diode illuminator coupled with an intensified camera, we
propose to control the LED headlights of future cars in a pulsed mode and to synchronize these pulses with a sensitive
camera. This paper shows some prototypes we've built and evaluates the performances of these different systems.
Furthermore, the problem of sensor saturation due to retroreflecting road signs is investigated and resolved by using a
Thermites are energetic materials which are made of a metallic oxide mixed with a reducing
metal1. The reactivity of classical thermites is moderate but it can be substantially improved
when micron-sized particles are replaced by nanoparticles.
In this paper, three examples of nanothermites are given in order to illustrate the contribution
of these nanomaterials in the future spatial and defence applications:
- the incidence of the size of the metallic oxide particles on the reactivity was illustrated by
the case of WO3/Al nanothermites,
- the correlation between the composition/structure of the oxide phase and the reactivity was
achieved on AlxMoyOz/Al nanothermites,
- the fabrication of Gas Generating Nanothermites was performed by adding military
explosives in porous mineral oxides (Cr2O3; MnO2) used to fabricate nanothermites.
An original compact test method of studying the influence of a modified Nd:YAG laser beam irradiation at the unusual wavelength of λ = 1.3 μm on IR-Ge-windows is investigated: optical parameters such as transmission loss, surface temperature during the laser irradiation, morphological deformation, and damage thresholds are measured in real time and compared with theoretical simulations. To study the thermal-mechanical relationship of the laser-matter interaction, an original pyrometer array is developed for the temperature-profile measurement and an original deformation experimental set-up, including a "line generator", is introduced. The damage behaviour of germanium at the wavelength of λ = 1.3 μm is also presented in this paper.
A measurement of the photoelectric parameter (contrast, pixels affected) degradation of visible Focal-Plane Arrays (FPAs) irradiated by a laser has been performed. The irradiation fluence levels applied range typically from 300 μJ/cm2 to 700 mJ/cm2. A silicon FPA has been used for the visible domain. The effects of a laser irradiation in the Field Of View (FOV) and out of the FOV of the camera have been studied. It has been shown that the camera contrast decrease can reach 50% during the laser irradiation performed out of the FOV. Moreover, the effects of the Automatic Gain Control (AGC) and of the integration time on the blooming processes have been investigated. Thus, no AGC influence on the number of affected pixels has been measured, and it has been revealed that the integration time is the most sensitive parameter in the blooming action. Finally, only little laser energy is necessary for the system dazzling (1 μJ for 152 ns). A simulation of the irradiated images has been developed using a finite-difference solution. A good agreement has been shown between the experimental and simulated images. This procedure can be extended to test the blooming effects of IR cameras.
An original compact test method of studying the influence of a modified Nd:YAG laser beam irradiation at λ = 1.32 μm on an IR-Ge window has been investigated: optical parameters, surface temperature, morphological deformation have been measured in real time and compared with theoretical simulations.
The present paper deals with the impact of pulsed laser radiation on dielectric and semi-conducting materials. Energy trans-fer leads to fast heating and thermal ablation. Mechanical stresses additionally cause deteriorations, cracks, fragmentation or perforation. These processes develop quasi-explosively even at low energy levels. Laser effects are discussed using microsecond(s) - to ps- pulses, acting both on optically passive and active materials (optical sensors). Evaluations of plasma-sustained en-ergy transfer by the impact of ns-pulses in comparison to ps-pulses are included as well. In the medium energy range by contrast, target effects are considered which require three to four orders of magnitude higher energies per pulse and corre-spondingly higher average powers which in the burst mode are determined by the repetition rate. The repetitively pulsed CO2-laser at ISL provides energies up to 150 J, repetition rates up to100 pps, an average power of 15 kW corresponding to peak power values of 75 MW for 2 microsecond(s) pulses. This laser provides a valuable tool, particularly suited for large area out-of-band target studies. Thermo-mechanical processes, as experimentally observed are discussed and compared with results of numerical simulation. Transparency changes of optics due to ablation as quantitatively measured by the modulation trans-fer function are further included in the discussions.
Experimental investigations of the effects of laser irradiation on the response (sensitivity) of HgCdZnTe photoconductors (p type) working at ambient temperature have been performed. In-band (band III) irradiation of these devices has been carried out with two collinear CO2 laser beams: a CW probe laser (beam diameter ? = 60 ?m) modulated by an acousto-optical modulator at a frequency of 500 kHz with a low energy output level giving the reference signal of the tested detector, and a second pulsed laser (named pump laser with ? = 300 ?m) used as the irradiation source. The pulse characteristics are a maximum energy of 200 mJ and a pulse duration of 2.5 ?s. These two CO2 lasers are part of an JR detector test bench design for experimental studies in JR band II (3-5 ?m) and band III (8-12 ?m) but only the experiments in band III are described herein. The irradiation densities range from 20 ?J/cm2 to 6.6 J/cm2. Both reversible effects, when the morphological damage threshold is not reached, and irreversible ones above this threshold have been observed. Moreover, it has been shown that irradiation produces a dramatic sensitivity decrease due to alloy concentration redistribution and thus causes a modification of the initial gap energy.
The modifications of the basic photoelectric properties in visible Si photodiodes irradiated by laser pulses have been measured and an attempt to link them to the observed/computed dopant distribution has been performed. These detectors have been irradiated 'in band' with two types of lasers: 1) a Q-switched Nd:YAG laser, frequency doubled with a 'short' pulse duration of 4 ns and 2) dye laser R6G with a 'long' pulse of 2 microsecond(s) . The single pulse fluence range extended form 0.4 to 50 J/cm2 well above the surface melting fluence threshold. Specially manufactured detectors have been tested. These detectors have a linearly graded junction with different resistivities. The detector responsivity decrease (DRD) vs applied irradiation fluence has been measured for both irradiation types. SIMS has been used to measure the changes in the dopant profile. It has been shown that a large spreading with a 'plateau like shape' of the boron distribution is obtained, resulting from a gas phase diffusion of dopant during the vaporization/condensation cycle. A relationship between DRD and boron profile has been established for Si detectors irradiated by the dye laser. A local sensitivity drop of 70 percent inside the damaged area location has been measured. Furthermore, it has been shown that high irradiation fluences induce a sequential loss of the different photoelectric properties rather than a complete detector breakdown at a prescribed fluence threshold.
A measurement of the electrical parameters degradation of Si photodiodes irradiated by laser visible light has been performed. The laser is a q-switched Nd:YAG, frequency doubled, operated in single pulse mode of 4 ns duration. The applied fluence levels range up to 90 J/cm2. Two kinds of irradiation process have been applied: either a part of the detector active area has been irradiated in single pulse mode, or a scanning of the whole detector active area has been performed with successive identical pulses. It has been shown that the fluence necessary to induce significant changes (local decrease of 35%) in responsivity is several times the surface melting threshold fluence (0.5 J/cm2). Conversely, the dark current is the most sensitive parameter, it increases by about four magnitudes for high irradiation. The in-depth dopant distribution is altered by high fluence irradiation in a way that cannot be explained by simple thermal modelization.
An experimental study of the damages induced by laser irradiation by different materials used as well as IR optics (germanium) or detector bulk materials (silicon) has been performed. The irradiation source is a repetitively pulsed Nd:YAG laser operating in fundamental mode ((lambda) equals 1.06 micrometers ) and single pulse selection. Instantaneous output power densities of 6 X 103 to 5 X 105 W/cm2 and pulse durations of 1 to 20 ms have been achieved. Different types of damages have been observed, depending on laser power density and spot size: mechanical fractures along privileged directions, ripples formation and principally surface protuberance rise as a sharp tipped peak during the melting pool resolidification when the laser is turned off. Emphasis is placed on the study of this last effect. We measure the final height of the resolidification peak and correlate it with target material and irradiation parameters. A numerical model of laser-material interaction including the density variation between the different phases has been used to correlate the experimental results. Qualitative agreement has been demonstrated for the surface growth time history.