KEYWORDS: Infrared imaging, Thermography, RGB color model, Near infrared, Visualization, Color, Education and training, Infrared radiation, Image fusion, Head, Deep convolutional neural networks, Deep learning
Infrared (IR) imaging sensors designed to acquire the 0.9 to 14 micrometers wavelength band offer unique advantages over the daylight cameras for a multitude of consumer, industrial and defense applications. However, IR images lack natural color information and can be quite challenging to interpret without sensor specific training. As a result, transforming IR images into perceptually realistic color images is a valuable research problem with a substantial potential for commercial value. Recently, various research works that use deep neural networks to colorize single mode (near or thermal) infrared images have been reported. In this paper, we present a novel convolutional auto-encoder architecture that takes multiple images captured with different imaging modes (near IR, thermal IR and low-light) to perform colorization using the visual cues that exist in all imaging modes. We present visual results demonstrating that using multiple IR imaging modes improves the overall visual quality of the results.
Heat-seeking missiles continue to be serious threats to aircrafts. In recent years, open-loop DIRCM systems have proven to be efficient countermeasures against these missiles. However, closed-loop DIRCM systems seem to be more promising as they employ a jamming code based on the classification or identification of an incoming missile through retro-reflection from the seeker head. In these systems, the retro-reflected beam is influenced by the optical turbulence in both transmission and return paths. In this paper, the influence of optical turbulence on the identification performance of a closed-loop DIRCM system is investigated. A dataset is created by varying the seeker spin and carrier frequencies along with the optical turbulence levels and range. Deep neural network classifiers were trained on this dataset and evaluated in terms of their effectiveness in identifying missile seekers with the DIRCM system.
Signal fading is a widely observed phenomenon in communication and sensing applications that results in spatially and temporally varying degradations in the received signal power. Specifically, for distributed acoustic sensing (DAS) applications based on phase sensitive Optical Time Domain Reflectometry (phase-OTDR), it is reported that optical signal fading is observed as random dramatic signal power fluctuations, which in turn cause substantial variations in threat detection sensitivity. In this paper, we study optical signal fading in the context of phase-OTDR based DAS from a signal processing perspective and analyze the undesired effects of fading on threat detection performance. Using a detailed phase-OTDR signal model, we analyze the effects of internal system parameters and external vibration source characteristics on optical fading. Based on these analyses, we define the conditions under which optical fading can manifest itself as a dramatic variation in threat detection performance.
KEYWORDS: Scattering, Optical fiber cables, Rayleigh scattering, Bragg cells, Signal attenuation, Light sources, Linear filtering, Signal detection, Light scattering, Signal to noise ratio
Extinction ratio is an inherent limiting factor that has a direct effect on the detection performance of phase-OTDR based distributed acoustics sensing systems. In this work we present a model based analysis of Rayleigh scattering to simulate the effects of extinction ratio on the received signal under varying signal acquisition scenarios and system parameters. These signal acquisition scenarios are constructed to represent typically observed cases such as multiple vibration sources cluttered around the target vibration source to be detected, continuous wave light sources with center frequency drift, varying fiber optic cable lengths and varying ADC bit resolutions. Results show that an insufficient ER can result in high optical noise floor and effectively hide the effects of elaborate system improvement efforts.
This paper presents a distributed acoustic sensing based linear asset protection system along with novel signal processing and threat classification techniques. The sensing system is realized by direct detection phase-OTDR (optical time domain reflectometry). An effective signal preprocessing approach for noise reduction that aims to improve the threat detection capability of the system is proposed. The proposed method is not limited to direct detection based systems and is applicable to any phase-OTDR system. A novel deep learning based threat clas- sification method is presented to identify various types of threats. The method uses a deep convolutional neural network trained with real sensor data. Experiments are conducted with an ITU-T G.652 fiber optic cable buried at one meter depth. The effects of applied preprocessing methods on both threat detection and threat classification performance are analyzed. The proposed preprocessing method is compared with the methods commonly used in the literature such as time differencing and wavelet denoising. The results show that by applying the proposed signal conditioning, event detection and classification methods, threat classification accuracies above 93% can be achieved with six typically observed activities, namely, walking, digging with pickaxe, digging with shovel, digging with harrow, strong wind and facility noise caused by water pipes, generators or air conditioning, at ranges of up to 40 km. The proposed classification strategy can easily be generalized for identifying different types of threats that are of interest in various security applications.
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