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2021 Vol. 43, No. 10

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Survey & Review
Analysis of Temperature Measurement Accuracy in Fever-Screening Thermograph
FENG Tao, JIN Weiqi, SI Junjie
2021, 43(10): 917-924, 967.
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Abstract:
The development and system composition of a fever-screening thermograph and the basic principle of a thermal imager's temperature measurement are introduced. It is observed that the thermal imager's internal radiation clearly influences the accuracy of the temperature measurement. This paper introduces an evaluation model for the temperature measurement accuracy of a fever-screening thermograph and its main parameters. By analyzing the relationship between these parameters and the thermal imager noise, the blackbody reference source, and the environment, the temporal and spatial low-frequency noise of the thermal imager are found to be the key factors affecting the accuracy of the temperature measurement. Moreover, the influence of temporal low-frequency noise can be eliminated using a blackbody reference source, and the influence of spatial low-frequency noise can be eliminated using the two-point correction method based on an external shutter. Thus, the fever-screening thermograph can meet the accuracy requirements of human body temperature measurement.
Systems & Designs
Focal Length Measurement of Ultraviolet Lens
DENG Jiayi, CHANG Weijun, WANG Nanxi, QIU Yafeng
2021, 43(10): 925-929.
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Abstract:
Optical lenses are the most basic components in optical instruments; focal length of the optical lens is the most important characteristic parameter, and accurate measurement of the focal length of the optical lens has long been a research focus. However, few studies have been conducted on the UV lens focal length measurement. In this study, a method for measuring the focal length of an ultraviolet lens based on a reflective collimator is investigated, according to the characteristics of the ultraviolet lens, and a few UV lens focal length measurement systems were designed. Different UV lenses were studied, and the focal length of the system was chosen for the measurement error analysis. The experimental results show that the measurement system can measure the focal length of the UV lens with high precision, i.e., the measurement error of 25-mm lens is 2.041%, that of 100-mm lens is 0.934%, which verifies the accuracy of the measuring system.
Effect of Antireflection Films on Diffraction Efficiency of Diffractive Optical Element
YANG Liangliang, XIA Yincong, LU Yucan
2021, 43(10): 930-933.
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The diffraction efficiency of a diffractive optical element(DOE) was analyzed with an additional phase introduced by an antireflection film, and the optimum design method of a DOE with an antireflection film was proposed. For a DOE working within the visible waveband, the diffraction efficiency was compared and analyzed using the proposed optimal method and traditional method. The results showed that the influence of the antireflection film on the diffraction efficiency and the bandwidth integral average diffraction efficiency(BIADE) of the DOE is not negligible. For the two working states of normal incidence and 30° oblique incidence, the BIADE of the DOE obtained by the optimal design method was higher than 94%.
Adaptive PID Control Method Based on Space Optical Mechanical Thermal Model
LI Shuai, YANG Baoyu, LU Yan
2021, 43(10): 934-939.
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Abstract:
To improve the temperature control stability of space cameras to ensure imaging quality, an adaptive proportional-integral-derivative(PID) control method based on a space optical mechanical thermal model is proposed. The design of the controller starts from the thermal balance equation of the space optical machinery and can correct the thermal model of the optical machinery in real time according to the temperature of the optical machinery and its radiating heat exchange object. Then, the parameters of the PID controller are corrected in real time using the pole assignment method, and the heating duty cycle of the temperature control period is finally determined. In this study, by establishing an abstract thermal model of space optical machinery and applying the above self-adaptive PID control method and PID control method with fixed parameters, the effect of temperature control is compared by simulation and experiment. The experimental results show that the adaptive PID controller always maintains the best dynamic response to the temperature fluctuation caused by environmental disturbance, and the temperature control stability is better than ±0.1 K; thus, the controller has better temperature control stability and environmental adaptability.
Modeling and Simulation of Jet-and Wake-Flow-Induced Velocity of Aircraft
YANG Libo, CONG Yan
2021, 43(10): 940-948.
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Abstract:
The jet-and wake-flow-induced velocities of aircraft were analyzed in this study. Wake vortex and jet flow models were established, and the induced velocity of the aircraft was simultaneously simulated in the wake flow field. Then, the flow field of the aircraft was computed via computational fluid dynamics(CFD), the results of which were compared with those of the wake vortex models. The comparison showed that the errors computed using the wake vortex models were large, which suggests that the wake flow field should be computed via CFD within 100 m of the aircraft tail; these results are consistent with the CFD results beyond 100 m from the aircraft tail, and the wake vortex models meet the accuracy requirements.
Guidance & Countermeasure
Test of Infrared Radiation Characteristics of Aircraft and Study on Launch Strategy for Infrared Decoy Flare
CHEN Shuheng, ZHU Niyao, CHEN Ning, MA Xianjie, LIU Jie
2021, 43(10): 949-953.
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Abstract:
This study aims to investigate the infrared radiation characteristics of aircraft and provide a reference for the launch strategy for infrared decoy flares. A spectral radiometer, middle infrared thermal imager, and far infrared thermal imager were used to test the static infrared radiation performance of an aircraft. Three test points were selected: the head, positive side, and tail. The test results showed the following: (1) at the radiation intensity and radiation area of the head were the smallest; (2) the infrared radiation intensity of the tail was the largest; (3)the radiation area of the tail was small; (4) the infrared radiation area of the positive side was the largest; and (5) the radiation intensity of the positive side was large. Based on to the test results, the strategy for infrared decoy flares was analyzed. Multi-point and area infrared decoy flares are used for stern attacks; area infrared decoy flares are used for lateral attacks; and multi-point and area infrared decoy flares are used for head-on attacks.
Image Processing & Simulation
Nighttime Dehazing Algorithm with Adaptive Global Brightness Compensation
CHEN Zhiheng, YAN Limin, ZHANG Jingyang
2021, 43(10): 954-959.
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To address the problems of color distortion, heavy texture loss, and poor dehazing effect in the dehazing images of hazing nights, this study proposes a night-time dehazing algorithm. Adaptive global brightness compensation, homomorphic filtering, contrast limited adaptive histogram equalization algorithm, and joint bilateral filtering were used to process the hazing images, and the dehazing images were obtained by combining the atmospheric scattering model. The experimental results show that this method has a better night dehazing effect and faster processing speed than the comparison algorithms. The contrast, mean gradients, and entropy are improved, and the color distortion and texture loss are effectively reduced.
Image Processing Method for Visual Simultaneous Localization and Mapping
YOU Tongfei, KONG Linghua, LIU Wenyu, YI Dingrong, YIN Jiang
2021, 43(10): 960-967.
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Simultaneous localization and mapping(SLAM) has always been a research hotspot in the robotics field. In recent years, remarkable progress has been made in SLAM research, but few SLAM algorithms have considered the processing of dynamic scenes. Therefore, in this study, an image processing method for dynamic target processing in a visual SLAM scene is proposed. The semantic segmentation algorithm based on deep learning was introduced into the ORB_SLAM2 method and input image classification processing was accomplished while removing the feature points on the body. Pose estimation was performed based on images with eliminated feature points. Compared to ORB_SLAM2 on the TUM dataset, the absolute trajectory error and relative path error accuracy were improved by more than 90% in the dynamic scene. To ensure the accuracy of the generated map, the applicability of the map was improved.
Indoor Human Fall Detection Method Based on Infrared Images and Back-Projection Algorithm
CHEN Han, YU Lei, PENG Sitian, NIE Hong, OU Qiaofeng, XIONG Bangshu
2021, 43(10): 968-978.
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Abstract:
Falls are reported to be a major cause of injury in China's elderly population. Shortening the time between the fall and subsequent treatment can reduce injuries caused by falls; therefore, the demand for indoor fall detection is increasing annually. Infrared image-based human fall detection methods are becoming increasingly popular owing to advantages such as being unaffected by light and non-intrusive. However, the traditional methods perform low accuracy because it is difficult to extract the features from the infrared videos at low resolution and high noise. Hence, this paper proposes an indoor human fall detection method based on a back-projection algorithm. First, the distance between the human body and the sensor is calculated using the human body temperature. Second, the height of the human body in the real world is reversely deduced using image information. Finally, the human body height data are smoothed and used for fall detection based on the height variation. The experimental results show that the detection accuracy of the proposed method is 98.57%, which is better than that of traditional projection methods. Therefore, it can be used for detection in real-life situations.
The Influence of Deep Transfer Learning Pre-training on Infrared Wake Image Recognition
ZHONG Rui, YANG Li, DU Yongcheng
2021, 43(10): 979-986.
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With lower underwater vehicle noise levels, the infrared imaging characteristics of underwater vehicle wake have become one of the main detectable sources. Using the infrared characteristics of underwater vehicle wakes to detect underwater vehicle traces has gradually developed into a popular detection method. Because of the low efficiency and inaccuracy of artificial wake characteristics identification, the adopted artificial intelligence deep learning method can be greatly improved. In this study, the infrared feature recognition of underwater vehicle wake is the primary focus. A sample set of mixed classes was made by image classification. The training effect of different pre-training networks was compared using migration learning. The influence of the internal parameters of the pre-training networks on the training effect of the wake was discussed. Finally, in the small sample set of 45 two kinds of wake, the recognition accuracy of the network after pre-training increased by 21.43%, the false detection rate decreased by 2.14%, and the positioning accuracy of the image with infrared characteristics was 18.18% higher than that of the visible image. This pre-training test has a certain application potential for future research on wake detection combined with convolution neural network recognition.
Improved Retinex and Multi-Image Fusion Algorithm for Low Illumination Image Enhancemen
ZHAI Haixiang, HE Jiaqi, WANG Zhengjia, JING Jiabao, CHEN Wenzhong
2021, 43(10): 987-993.
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To solve the problems of poor image quality and low contrast in low-illumination image enhancement, this study proposes an improved Retinex and multi-image fusion algorithm for low -illumination image enhancement. First, the image to be processed is converted to the HSV color space, and the brightness of the V-channel component is adjusted by setting a threshold. Then, it is converted to the RGB color space, and three copies are made. Histogram equalization and median filtering are performed for the first part; the second part is processed by automatic brightness adjustment and bilateral filtering; the third part is processed by an improved Retinex algorithm, which uses Gaussian filtering and bilateral filtering as its surround function to estimate the illumination component of the image, and outputs the reflection image. The three processed images are transferred to the HSV color space, and the V component is fused. The H and S components follow the values of the second image component. Finally, the fused image is converted from the HSV to RGB color space, and the processed image is output. The experimental results show that the proposed algorithm not only enhances the low-illumination image but also suppresses the image noise. Furthermore, it exhibits good edge preservation and obvious details.
Infrared Image Segmentation Based on Improved Spotted Hyena Optimizer
LI Tangbing, HU Jinhong, ZHOU Qiukuan
2021, 43(10): 994-1002.
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Abstract:
Based on the shortcomings of the spotted hyena optimizer (SHO), falling into a local optimal solution or a low-quality solution is easy. In this study, the Lévy flight and simplex method are proposed to improve the SHO(Lévy_SM_SHO). Comparing Lévy_SM_SHO to Lévy flight spotted hyena optimizer (Lévy_SHO), simplex method spotted hyena optimizer (SM_SHO), and spotted hyena optimizer (SHO) on the test function, the experiment proves that the improved algorithm can achieve better optimization results. Finally, the Lévy_SM_SHO algorithm is applied to the infrared image threshold segmentation problem. By crosschecking the segmentation results with the particle swarm optimization algorithm (PSO), we proved that the Lévy_SM_SHO algorithm can achieve better threshold segmentation results.
Human Fall Detection Method Based on Key Points in Infrared Images
XU Shiwen, WANG Heng, ZHANG Hua, PANG Jie
2021, 43(10): 1003-1007.
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Abstract:
To address the problems with existing human fall detection methods for complex environments, which are susceptible to light, poor adaptability, and high false detection rates, an infrared image human fall detection method based on key point estimation is proposed. This method uses infrared images, which effectively eliminates the influence of factors such as lighting; first, the center point of the human target is found through a neural network, and second, the human target attributes, such as the target size and label, are regressed to obtain detection results. An infrared camera was used to collect human body fall images in different situations and establish datasets containing infrared images of human falls. The proposed method was used for experiments; the recognition rate exceeded 97%. The experimental results show that the proposed method has a higher accuracy and speed than other two methods in infrared image human fall detection.
Low-Light-Level
Design of Image Intensifier Photocathode Gating Module
DU Peide, ZHU Wenjin, ZHOU Shengtao, LI Xiaolu, LI Yaqing, CHU Zhujun, YANG Kejie
2021, 43(10): 1008-1013.
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Abstract:
For high-speed imaging framing cameras, nanosecond-level time resolution can be achieved using a photocathode gating module to control the image intensifier photocathode. Traditional modules have some problems, such as slow switching speed, exclusively negative voltage output, and positive or negative voltage outputs that cannot reach the full amplitude. Based on the CMOS push-pull output structure and voltage level transfer circuit, a photocathode gating module was designed, which could use a low-side driver driving PMOS and NMOS. Dead-time control was used to avoid cross conduction of the upper and lower MOSFETs. The actual test results verified that this module has the advantages of simple structure and reliable performance; moreover, the ns level rising or falling edge, adjustable duty ratio 0 to 100%, and +30 to -200 V pulse output amplitude were realized. This module was found to be suitable for gating the photocathode of the image intensifier.
Refrigeration
Theoretical Analysis and Matlab Simulation of Dynamic Vibration Absorber for Single-Piston Linear Compressor
KONG Derui, XIA Ming, LI Haiying, CHEN Jun, ZHAO Peng
2021, 43(10): 1014-1021.
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Abstract:
Single-piston linear Stirling cryocoolers are widely used in infrared detectors owing to their fast cooling, lightweight, and high reliability. However, the vibration generated by the compressor during operation considerably affects the imaging quality of the detector. Therefore, the use of a dynamic vibration absorber has become the best vibration reduction method for single-piston linear compressors. First, this article discusses the role of a dynamic vibration absorber in damping single-piston linear compressors and provides an example of the basic structure of current single-piston linear compressors. Second, to generalize the theoretical analysis, several important dimensionless parameters are introduced in the theoretical calculation of the dynamic vibration absorber and compressor vibration model. Finally, Matlab is used to simulate the vibration amplitude-frequency characteristics of the dynamic vibration absorber and compressor model

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