In this paper, the authors try to determine a procedure for the best choice in selecting one or other type of sensors as a function of the object under observation, background and environmental conditions. In surveillance activities related with different missions and scenarios occurred in day and/or night time, the proper choice and use of video surveillance sensors is of huge importance. Starting from specific scenarios of surveillance, as for example the surveillance of the sky to detect drones, or surveillance of the ground area to detect some manmade objects or intruders, this paper approaches the problem of the image appearance in VIS, SWIR and LWIR spectral ranges, using different passive technologies of surveillance. Relevant images are comparative presented in relation with some theoretical quantifications made through mathematical models or through software simulations.
Starting from a few targets and backgrounds with known spectral reflectivity or emissivity, the contrast was used to show its influence on the signal strength reaching the surface of the video detector (imager) in similar environment conditions. Finally, the authors seek certain characteristics of the electro-optical system itself that can influence most the strength and quality of the optical signal with respect to influences on observation distances of the target. The possibility of using an active technology instead of a passive one, by introducing a pulsed laser illuminator, is also analyzed. The use of some polarizing filters is also considered but in this stage only in laboratory conditions, in order to improve the observability of an object in some special environmental circumstances.
The purpose of this paper is to establish an evaluation method of the observability performance for equipment that
enables day and night vision (using thermal cameras, gated image intensification and CCD cameras using L3V based on
e2v technology). This is done by modelling of experimental results of simulation setup in the lab.
Starting from the predictive evaluation procedures of the observation, the paper analyses the relevance of method to
establish the limits in the utilization of the above- mentioned equipment, from the point of view of the observation
probability, in difficult ambient conditions, such as reduced illumination level or aerosol curtains.
Moreover, the present work compares subjective factors that can influence the prediction by the participants on the
experiments (age, training, decision time) and objective factors (contrast between background and image, resolution of
the observation system and image noise).
KEYWORDS: Cameras, Electron multiplying charge coupled devices, Humidity, Sensors, Reticles, Visibility, Air contamination, Video, Modulation transfer functions, Visibility through fog
The reaction time to the occurrence of unexpected events is essential in night-time driving which uses thermal cameras
and EMCCD cameras. The present work analyses the implications of monochrome and coloured observation, of in-depth
perception of the distance field, of visual accuracy of the display characteristics that the image is shown on, and of the
detection matrices corresponding to the two cameras. The paper also looks at the significant impact of the ambient
humidity on the fatigue increase due to prolonged observation. The study also contains a comparative analysis of the
observation with, and without a reticle in the evaluation of distance elements from the observed scene. The experiments
the present study is based on have been realised using a simulation software in LabVIEW. The work presents
also particular case studies to be used in the practical analysis of the reaction time to the driving of vehicles and
monitoring their traffic during day or night, with the display of the image on LCD. The experiments were based on films
acquired in different ambient conditions, with clear atmosphere, with fog or snowing.
The paper presents an evaluation methodology and the results of some experiments that have been made in laboratory in
order to determine the target's detection's probability depending on the target's contrast and the observers' age. The
main goal was to assure the model for an optimal feature's configuration for a device used to enable the view during
day or night, so that we can estimate, within improper view conditions, its visibility boundaries during day and night.
The base of method's principle is the Bayes' theorem, and the authors have used in their experiments the technique of
estimation by probability of real positive and real negative that is also used in medical evaluation of images. The authors
have used an instrument layout in the laboratory that included an uncooled 8- 12 μm thermal camera, a CCD and a ICU
camera, an USAF pattern and a set of chemical compositions that produce aerosols with different concentrations. It has
been proved that the detection probability decreases proportionally by age, but being differentiated by the contrast
between the target and the background; it has been presented the diagram of the probability variation and the analytical
relationships that approximate it, in terms of contrast and aerosols' concentration features.
The authors have approached some system design problems to achieve an interval of spatial resolutions for different characteristics of the observed scene, in which the observation probability can vary because of the thresholds of observation conditions. The paper proposes a simple analytical model for the estimation of the observation range (on the base of an imposed value for the observation probability), starting from a Boltzmann approximation which extends the observation prediction model based on the Johnson's classic criterion. Supplementary, several real image scenes, at different known observation ranges, were acquired on PC and also some patterns at different thermal contrasts, in laboratory conditions. The results of experiments have been extended into a function similar to the initial model proposed and which depends on the thermal camera used. The observation range was modelled, not only depending of target dimension and system resolution, but by the observation probability and the difficulty degree of observation, too. The deterioration of the thermal contrast has been simulated with image processing software, by a contrast controlled degradation of image, to estimate the observation probability in different environmental conditions. By a graphic-analytical optimization one can select some spatial resolution values which assure desirable acquisition probabilities of the targets at different thermal contrast values of the scene. The observation probability was analyzed for detection, recognition and identification.
The process of medical unconventional diagnosis is started by the user through a search process of appearance of some possible areas of abnormal temperatures which can be seen on a suitable monitor and the comparison of these areas with the unaffected ones. To guarantee an increased successful of this search process is necessary that the system design to take into account those displaying modalities of thermal images in order to highlight critical areas. These areas are all the more so full of information as: calibration of the system is more strictly achieved; image is rather well-defined, both geometrical and thermal (through depth and colour conversions).
The present paper is made up as a contribution to the existing methodologies in calibration process of such a system. The authors leave from the reason that the existence of a set of calibration filters can contribute with sufficient data which can compensate the inherent errors cam e out by the use of a blackbody source at different temperatures necessry to calibration. Starting from the reasons mentioned above can be demonstrated that is sufficient to have a source constant temperature for the assurance of a strictly calibration.
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