2022, Volume 44, Issue 4
2022, 44(4): 315-327.
Typical individual combat scenarios were presented, which include battlefield observation, reconnaissance and surveillance, target positioning and laser designating, light weapon precise shooting, sniper warfare, fighting with targets hidden in trenches, parachuting and airlanding at night, night fighting, entering indoor or dark underground space from the bright environment, observing/searching/shooting in the low-visibility environment. To meet these battle requirements, individual soldier night vision goggles have been developed to integrate with visible light scope, laser rangefinder, satellite positioning system, digital compass, communication and other functional modules. Therefore, night vision goggles possess more complex and accurate combat capabilities, such as night vision imaging, range finding, positioning, calculating, information fusion, fire control computing and wireless transmission.
2022, 44(4): 328-342.
Terahertz (THz) waves are located between the infrared and microwave bands. Compared with other bands, they have the characteristics of high transmission, low energy, coherence and transient nature. With the widespread application of terahertz imaging technology in the fields of space communication, radar detection, aerospace and biomedicine, it has been shown that THz imaging offers advantages over traditional imaging technologies (such as ultrasonic imaging and X-ray imaging). This paper first introduces the development status of THz time-domain spectroscopy (THz-TDS) imaging technology and room temperature (uncooled) microbolometer THz imaging technology. Subsequently, typical applications of THz imaging technology are presented. Finally, the limiting factors of THz imaging technology are discussed.
2022, 44(4): 343-350.
Avalanche photodiodes (APDs) have been widely used in high bit rate, long-distance optical fiber communication systems because of their high sensitivity and gain bandwidth. The excess noise generated in the avalanche process has a significant impact on the sensitivity of APD. Therefore, the study of excess noise is crucial for the improvement of APD performance. The existing methods for testing excess noise of avalanche photodiodes primarily include direct power measurement and phase-sensitive detection. This article briefly introduces these testing methods, analyzes their advantages and disadvantages, and summarizes the state-of-the-art testing methods. Additionally, three methods to reduce excess noise are summarized: choosing materials with low impact ionization coefficient, using relaxation space to change the thickness of the multiplier layer to reduce the number of impact ionization of carriers and engineering the APD for appropriately heterogeneous impact ionization.
2022, 44(4): 351-356.
An Al2O3 film was prepared as a dielectric layer for an InSb material via the atomic layer deposition technique, the MIS device was developed, and the effects of annealing temperature on the post-metallization interfacial characteristics were investigated. Moreover, the interface of the MIS device was characterized using the C-V test. The results indicate that the Al2O3 dielectric layer introduced surface-fixed positive charges, and annealing processing at 200 and 300℃ can effectively reduce the slowing density. Furthermore, Terman's method can be used to obtain the interface states density distribution. This indicates that 200℃ annealing can significantly decrease the interfacial density close to the center of the bandgap and the conduction band. Additionally, negative charges being trapped near the interface of the Al2O3 dielectric layer is found to be the main cause of C-V curve hysteresis. Experiments prove that an annealing process at 200℃−300℃ can effectively improve the InSb/Al2O3 interface quality.
2022, 44(4): 357-363.
Aiming at the serious image distortion of elliptical orbit infrared surveillance system and the low precision of target confirmation algorithm based on image registration, a novel target confirmation method based on line of sight (LOS) vector sequence is proposed. By establishing the state transition model and observation model of target LOS vector sequence, the GM-PHD filter is used to filter LOS vector sequence data and confirm target. Owing to that the GM-PHD filter will lose the new target when its states are unknown, the feedback GM-PHD filter is proposed. The simulation results verify the effectiveness of the proposed method based on LOS vector sequence and the timeliness of the improved GM-PHD feedback filter for new target states estimation.
2022, 44(4): 364-370.
Improving the temperature adaptability of optical mechanical structures is of great significance for space cameras to improve thermal control and stability of the system. Using a uniform material structure to eliminate thermal variation in the system, the optical and mechanical structure of a space camera in the visible light band is designed with aluminum alloy materials. Under actual working conditions, a uniform temperature of 20℃±15℃ was attained. Modulation transfer function (MTF) is greater than 0.3 at 71.4 lp/mm when the image changes in a different direction to gravity. The typical material matching schemes are comparatively analyzed. The stability of the all-aluminum structure under identical working conditions is far superior to that of structures using different materials, which verifies the effectiveness of the optical and mechanical structure of the unified material in terms of temperature adaptability.
2022, 44(4): 371-376.
Infrared panoramic search and track systems can provide real-time multi-target search and positioning functions for a 360° field of view. However, the involvement of the large view field introduces problems such as increased number of false targets and a large displacement of moving targets between panoramic frames. To address these problems, this study uses the image pyramid transform to reduce the panoramic image resolution and the Lucas-Kanade optical-flow method to calculate the optical flow of all predicted movement areas. Finally, the optical-flow features are analyzed to separate the real target from the false target area. In this way, false targets can be effectively detected in the panorama images, and the interference of such targets in the subsequent processing can be eliminated.
Analysis of Resolution Change of the Super Gen.Ⅱ Image Intensifier with Input Illumination Variation
2022, 44(4): 377-382.
The resolution of image intensifier samples with different limiting resolution, signal-to-noise ratio, and equivalent background illumination were tested under different illuminations to study the variation of the resolution of Super Gen.Ⅱ image intensifier. By analyzing the test data, the influence of limiting resolution, signal-to-noise ratio and equivalent background illumination on resolution under different illuminations were obtained. The results show that in the range of 5×10−2 to 5×10−3 lx, the resolution of the image intensifier with different performance parameters is identical to its limiting resolution, and the resolution does not decrease with decreasing illumination. In the range of 5×10−3 to 5×10−7 lx, the resolution differs from its limiting resolution, and the resolution decreases with decreasing illumination. In the case of resolution decreasing with illumination, the higher the signal-to-noise ratio and the lower the equivalent background illumination, the lower the rate of resolution decrease, and the resolution reamains relatively high. In the illumination range of 5×10−3 to 5×10−6 lx, signal-to-noise ratio has a greater influence on the resolution, whereas in the illumination range of 5×10−6 to 5×10−7 lx, the influence of equivalent background illumination is greater. As the image intensifier is mainly used in low light conditions, the resolution under these conditions is more important. To increase the resolution of the image intensifier in the illumination range of 5×10−3 to 5×10−7 lx, it is necessary to improve the signal-to-noise ratio and reduce the equivalent background illumination as well as the limiting resolution.
2022, 44(4): 383-388.
Brightness gain is an important parameter of low-light image intensifiers. It affects the accuracy of the object-background contrast in low-light night vision environments. Based on the principle of contrast tests, this study analyzes the relationship between the brightness gain and the object-background contrast, as well as influencing factors, via the object-background contrast test on an ICCD with different brightness gains. The results show that when the brightness gain is 12000, 8300, or 6000 cd/(m2·lx) and the ambient illuminance is within the range of [2×10－3, 8×10－3] (lx), the object-background contrast is minimally affected by the brightness gain. However, when the illuminance is outside this range, the object-background contrast test result may be distorted due to the influence of the brightness gain. The results of this study can guide the improvement of accuracy of ICCD object-background contrast tests.
2022, 44(4): 389-396.
There are several variable parameters in the existing low light level sight range model which makes it difficult to predict the target reconnaissance ability in an actual complex nighttime environment. Based on the Ross equation, atmospheric optical transmission and long-distance reconnaissance image contrast model, this study proposes a method to predict the reconnaissance ability of specific targets using a standard target contrast test, and the standard target contrast curve under specific night light environment is provided. With the contrast curve and minimum resolvable contrast (MRC) model, the reconnaissance distance of tank and truck targets is predicted. After comparing the predicted value with the actual test value, the error is within 16.2%, which verifies the feasibility of using standard target contrast to predict the target reconnaissance distance. The results have value in guiding the analysis and evaluation of low light level equipment reconnaissance capability under different backgrounds and environments.
Multiscale Retinex Infrared Image Enhancement Based on the Fusion of Guided Filtering and Logarithmic Transformation Algorithm
2022, 44(4): 397-403.
Problems such as blurred edges and poor contrast in infrared images acquired by an infrared imager lead to poor visual effects and low image quality. Based on the multi-scale Retinex (MSR) algorithm, a MSR infrared image enhancement method based using guided filter edge preserving and gradient preserving is proposed. Firstly, a guided filter is used in place of the Gaussian filter in the MSR algorithm to estimate the illuminance component. Secondly, the illumination component is processed via logarithmic transformation, expanding the low end of the gray scale and compressing the high end. Finally, the detail layer image obtained using guided filtering is linearly amplified and superimposed with the MSR processed image to obtain an enhanced infrared image. Experimental results demonstrate that the proposed algorithm can effectively improve the quality of infrared image compared with the conventional MSR algorithm and guided filter.
2022, 44(4): 404-409.
In recent years, image fusion technology has been widely used in the power industry. Different types of image sensors are used to collect images of power equipment and transmission lines. Through the fusion of infrared and visible light images, intelligent inspection and fault analysis of power equipment and transmission lines can be realized. This article first briefly introduces common image fusion algorithms and fusion image evaluation standards. A multi-scale image fusion algorithm based on adaptive weighting is proposed, which uses the registered visible light and infrared images to perform multi-scale wavelet decomposition. According to the different image characteristics of high and low frequencies, the low frequency adopts the adaptive weighted fusion rule and the high frequency adopts the fusion rule with the largest absolute value. The fused wavelet coefficients are inversely transformed to obtain a new fused image. Subjective and objective evaluation and analysis of the fusion image confirm that the fusion algorithm solves the integrity problem of the image collected by a single image sensor, enhances the detailed information of the fusion image, and improves the confidence of the scene.
2022, 44(4): 410-420.
The real-time images collected by imaging systems in low illumination environments suffer from low illumination, severe noise and poor visual effects. To improve the image quality in low light environments, this study proposes a low-light image enhancement method based on a multi-scale wavelet U-Net. This method uses multi-level encoders and decoders to construct a U-Net and introduces the wavelet transform to develop a unit for frequency decomposition of features. This improves the perception of illumination and texture by separating high-frequency and low-frequency information. Multi-scale perceived loss is designed to guide the learned mapping of step-by-step reconstruction from low-frequency information to high-frequency information, thereby optimizing the convergence and performance of the network. Finally, the proposed method and comparison methods are tested on the LOL, LIME, NPE, MEF, DICM and VV datasets. The experimental results demonstrate that the proposed method can effectively brighten images, suppress image noise and texture loss, and improve the PSNR, SSIM, LOE and NIQE metrics. The proposed method exhibits better performance than other comparison algorithms in subjective and objective evaluation.
2022, 44(4): 421-427.
The monitoring of rail safety status is crucial to ensure the safe operation of trains. Aiming at rail crack detection, this study quantitatively compares different crack detection technologies and analyzes the application of infrared thermal imaging technology in rail crack detection. The proposed detection technology comprises three parts: external excitation heating, infrared image acquisition and image processing. Firstly, the common excitation methods are introduced and compared. The application of halogen lamps as excitation sources in crack detection is described in detail. Secondly, a halogen lamp excitation based infrared thermal imaging detection experimental platform is developed. Thirdly, an improved image processing algorithm is proposed to enhance the collected infrared image. Finally, this study discusses the prospects of applying the proposed technology in the future.
2022, 44(4): 428-436.
To solve the problems of inconvenient carrying and contact with the human body when using current clinical vital signs monitoring equipment, a method of estimating heart rate and respiratory information is proposed by analyzing the facial vascular model and temperature difference of the nostril position using an infrared thermal imager as a transmission device. First, the foreground target is extracted from the obtained thermal image sequence to shorten the time of face detection in the entire image. Anisotropic diffusion is then used to enhance the contrast of the vascular position in the region of interest, and the gray mean of the vascular position in the face is obtained by morphological processing to form the initial heart rate signal. Finally, trend elimination, wavelet threshold denoising, and other filtering methods were used to remove the trend item and random noise in the time series to obtain the final heart rate waveform, dynamic heart, and respiration values. Compared with specialized equipment in the hospital, it was found that the method exhibited a heart rate error of less than 4%, and the average error of the average value was 0.718 beats/min. The breathing error is within 1 beat/min, showing high accuracy and robustness and that the method can meet actual needs.