2021 Vol. 42, No. 3
With the unique advantages of strong maneuverability, high efficiency-cost ratio, and unmanned characteristic, the unmanned aerial vehicle (UAV) equipped with the photoelectric countermeasure system is applied to the unmanned electronic warfare and seize the initiative on the battlefield, which is the hot spot of the current development of photoelectric countermeasure. The application of photoelectric countermeasure technologies such as photoelectric reconnaissance warning, electronic suppression and jamming, and photoelectric stealth in UAV platforms was analyzed. It focused on the development trend of photoelectric technology in UAV platforms in terms of miniaturization, lightness and standardization. The prospect of UAV swarm technology and intelligent photoelectric countermeasure system to play the role of photoelectric countermeasure in the future complex war environment was looking forward.
Modern war requires that the battlefield target search equipment can quickly and automatically search, discover and identify the long-distance targets under the condition of mobility, and sorts the threat of enemy targets, then accurately locates the coordinates of the targets, and transmits the target information to the rear. A new type of sighting system for armor vehicles was proposed. The five modules of the system, panoramic module, visible continuous zoom module, high-performance infrared thermal imager module, intelligent control module and pan tilt zoom (PTZ) optical mechanical module were studied and designed. In addition, the composition, principles and key technologies of the system were discussed. The results of functional test and precision test after prototype development show that the integrated sighting system has correct principle, high reliability, stable accuracy as high as 0.06 mil (1σ), and strong rapid response ability, which provides a cost-effective way to realize the anti-terrorism of armor vehicles.
With the rapid development of science and technology, the infrared reconnaissance equipment is widely used in airborne platforms. There is an obvious mismatch in operating distance of infrared sensor and laser sensor in typical airborne infrared equipment, which can't accurately locate the ultra-long distance targets. In order to realize the high precision location of long distance or ultra-long distance targets under the conditions of distance deletion, the method of passive location based on multi-platform collaborative detection was proposed. The simulation results show that the passive location algorithm based on multi-platform collaborative detection can effectively realize the high precision targets location, and the location precision is about 7%R, which is superior to that of traditional TDOA and DOA methods.
According to the development demand of miniaturization and lightweight for airborne photoelectric weapons, an infrared and laser system was designed with the common optical path. The infrared waveband of the system was 3 μm~5 μm, and the F number was 2. The surface array detector with a medium wave of 640×512 pixels was adopted, and the pixel size was 15 μm×15 μm. The laser emission and infrared optical path used the common telescopic system. By using cubic prism, the scanning in the range of azimuth 360° and pitch 0°~90° was realized by optical system. The common optical path design could reduce the size of the mirror and lens in the optical path, which had the characteristics of compact structure and small mass. It was focused on the problem of introducing the laser back scattering by the optical elements in common optical path. The joint optimization method of CODE V and LightTools was adopted to avoid its influence, which could ensure the good imaging performance of optical system.
Since the jamming strategy of traditional infrared imaging anti-ship missile, such as hot flame bomb and smog, which could not be good deal with the threat of new infrared imaging anti-ship missile, a strategy of applying water curtain to different zones of ship surface to counter the infrared imaging anti-ship missile was designed, and the jamming effect of water curtain on infrared imaging seeker was studied by modeling and simulation. The simulation model of ship infrared radiation which comprehensively considered the sea-sky background was established, and combined with the typical image recognition algorithm, the different water curtain application strategies were developed. The simulation model was used to study the success rate of infrared imaging seeker for target recognition under a certain distance and different strategies. According to the recognition results and algorithm principle, the water curtain application strategy was optimized. The optimized partition water curtain application strategy could reduce the recognition success rate of the seeker to target by about 60%. Finally, the cooling effect of water curtain was verified by the cooling shrinkage ratio test device built in the real scenes.
Retina-like scanning has the advantages of rotation and scale invariance, redundant data compression and variable resolution information acquisition. The traditional method of retina-like scanning has the disadvantages of complex system structure and slow scanning speed. Therefore, a method of retina-like scanning based on the distortion of lens and rotation of Abbe prism was proposed to realize the scanning ring growth and target field scanning. The distortion of lens could enlarge the incident spot with different fields of view to realize the retina-like spots structure. The initial parameters of the lens were solved by the objective-image relationship, and the aspheric parameters of the lens could be optimized with the growth coefficient between the rings of the scanning spot as the objective function of lens distortion optimization. The focal length of this system is 14.24 mm and the working distance is 25 mm. The simulation results show that the retina-like scanning with 16 circles can be realized on the image plane with the diameter of 27.66 mm, when the incident laser is a 1×16 linear array laser with the height of 20 mm. And the maximum ring growth coefficient of the scanning spots is 1.08. Compared with the retina-like scanning system, this method has the advantages of low cost, simple structure and fast scanning speed.
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Using chalcogenide glass and binary diffraction surface, an infrared athermalization system based on the uncooled long-wave infrared detector (1 024×768 pixel) was designed. The system was composed of 3 pieces of glass, and the system had a focal length of 75 mm, an F −number of 1, a total length of 97 mm, and a total weight of 203 g. The simulation analysis using ZEMAX shows that, within a temperature range of −40℃～50℃, the modulation transfer function（MTF）value at the Nyquist frequency (42 lp/mm) of the system is greater than 0.37, which is close to the diffraction limit; between −70℃ and 70℃, the MTF at the system Nyquist frequency (42 lp/mm) under temperature can also meet the requirements. The system has the characteristics of large relative aperture, excellent full-field image quality, lightweight structure, and good manufacturability.
Aiming at the problem that high throughput and high spectral resolution cannot be realized simultaneously in the existing space-borne scanning spectral imaging, a Fabry-Perot (FP) micro-array and compressed sensing spectral imaging method was proposed. By adding FP micro-arrays in front of the imaging detector, each unit of the FP micro-array modulator was corresponding to the different heights, and then the input optical signal was modulated to obtain the different spectral responses. Combined with the scanning and compressed sensing restoration algorithm, the hyper-spectral image data cube was finally obtained. The spectral range of the system was 400 nm~700 nm, and the number of spectral channels was as high as 700. By comparing the simulated laser incident spectrum with the compressed sensing reconstructed spectrum, the simulated mean square error (MSE) was 0.002. In addition, the two monochromatic light spectra with different colors were reconstructed by experiments. The experimental results were basically consistent with the spectrum measured by the standard spectrometer, which verified the feasibility of the spectrum reconstruction by this method. This method can be widely used in the measurements of high throughput, hyper-spectral space-borne or scanning spectral imaging.
The flexible support is the key component of fast steering mirror. The kinematic design of flexible support for fast steering mirror was introduced. According to the spatial relationship between constraints and degree of freedom, the mode of constraints and degree of freedom of flexible support was determined. The slender rod was used as the constraint element to construct four configurations of flexible support for fast steering mirror, and two new types of flexible support structures were obtained based on the classification of existing fast steering mirror mechanisms. The research results can provide guidance and basis for mechanism selection, optimization and engineering design.
The stable tracking of small infrared targets in the complex backgrounds such as ground, sea surface and sky is an urgent problem to be solved. Taking into account both the robustness and real-time performances, based on the discriminative scale space tracking algorithm, the generalized structure tensor algorithm was applied that could effectively characterize the gray-scale mutation characteristics of the target area and the target shape information as a feature extraction method. The improved algorithm was more suitable for the rapid infrared image processing, which could improve the tracking robustness, and had a small amount of calculation, high efficiency, and low target feature dimension. In order to improve the stability of the model, it was decided to track the model update according to the confidence level, so as to avoid the model being disturbed by the wrong samples. Compared with the discriminative scale space tracking algorithm, the proposed algorithm has significant advantages in accuracy, real time and robustness, and achieves a tracking speed of 300 fps @256×256 pixels of image.
Aiming at the problem of stray light interference in ground-based visible light observation images, a stray light noise removal method of star maps based on intensity prior was proposed. First, by analyzing the causes of stray light and its spatial distribution characteristics in star maps, a degradation model of the star maps under stray light interference was established; then, the intensity prior of star maps was used to estimate the depth information of the atmosphere and remove the unevenly distributed stray light noise; finally, the method was verified on the actual star maps taken by the ground-based optical telescopes. Compared with the existing algorithms, the proposed method obtained better experimental results in terms of background suppression and target signal-to-clutter ratio (SCR) improvement for targets interfered by different degrees of stray light. Among them, for the space target with a SCR of 2.05 or more in the sequence star maps, the proposed method can obtain the SCR gain of 7.39 or more and the background suppression factor (BSF) of 1.92 or more after processing.
The low-speed and small unmanned aerial vehicle (UAV) detection system based on photoelectric sensors can quickly and accurately find and identify the UAV targets. However, the proportion of pixels in the images of long-distance non-cooperative UAV targets is too small, and the degradation of characteristics is obvious, which greatly reduce the recognition rate. The image super-resolution technology can obtain the high-resolution images from low-resolution target image regions and restore the more detailed features. The existing super-resolution technology is difficult to be compatible with the high and low frequency characteristics of images while ensuring the inference speed. In order to meet the requirements of detection system, based on the feature extraction and nonlinear mapping network structure of fast super-resolution convolutional neural network (FSRCNN), and combined with the multi-scale fusion, a lightweight multi-scale fusion super-resolution network with 4 branches was proposed, which could be compatible with the high and low frequency image information in super-resolution graphics and with low parameter quantity and high real-time performance. The experimental results show that the UAV contours and details with high resolution can be reconstructed more quickly and efficiently by this algorithm. In the experiment of YOLOV3 detection effect, the confidence degree of the UAV detection can be increased by 6.72% by this algorithm, which has high practical application values.
The infrared image is a commonly used image source of modern optical equipment, the display effect of the image directly affects the user experience of the device, and the noise in the infrared sequence images can cause the decline of display effect. In order to reduce the effect of noise on the display effect of infrared sequence images, by weighting the gray values of multiple historical frames and estimating the noise-free image of the current frame, a denoising algorithm based on the temporal Gaussian filtering was proposed. Referring to the weight distribution method of spatial bilateral filtering, the influence of the gray value was introduced to correct the weight of temporal Gaussian filtering, which solved the trailing and blurring of moving targets in sequence images caused by the temporal filtering. The experimental results show that the temporal filtering method can effectively smooth the noise between frames and reduce the deterioration of display effect of the infrared sequence images caused by the noise; and the problem of trailing and blurring caused by the temporal filtering can be solved with the influence of gray value which is introduced to correct the filtering weight.
The slope information of ski resort is not only a necessary content for planning and construction of ski resort, but also an important data support for skiers to improve performance and reduce sports injuries. The traditional manual measurement method is time-consuming and the low temperature environment of the ski resort is not conducive to the long-time operation of the surveyors. In order to solve the problem of calculating the slope of ski tracks, an automatic slope extraction algorithm of ski tracks based on LIDAR point cloud was proposed. The projection difference of elevation filtering, clustering segmentation and other algorithms were used to preprocess the ski resort point cloud and obtain the feature data of ski tracks edge. An adaptive threshold fitting algorithm was proposed for the extraction of the center line of ski tracks. This algorithm could automatically select the threshold to fit the center line of ski tracks according to the point cloud quantity information and coordinate information, which eliminated the negative effect of the data sparse or missing of point cloud on the center line fitting. The data processing results show that the relative error between the slope value calculated by this method and the average value of multiple manual measurements is 2.2%. This method is of reference significance to the application of LIDAR in the target of ski resorts and to the calculation of slope of snow tracks in the mapping of ski resorts.
The chemical oxygen demand (COD) is a parameter that can quickly detect the organic pollutants and can well reflect the degree of water pollution. A COD content estimation model of multi-feature fusion water based on transmitted spectrum measurement was proposed. The transmission hyperspectral method collected 100 groups of COD water spectral information, preprocessed the spectral data, selected the characteristic band, analyzed the influence of different preprocessing methods on the model accuracy, carried out the feature fusion, and established the BP neural network model. By comparing the accuracy of the model, the optimal model was selected to detect the water COD content. The results show that the decision coefficient R2 of BP neural network model based on multi-feature fusion is 0.991 64, and the root-mean-square error (RMSE) is 0.030 9. Compared with the partial least square method, the model has higher goodness of fit and higher accuracy.The multi-feature fusion based BP neural network hyperspectral detection method can realize the detection of COD content in water, and can be applied to the detection of other components in water.
For the variable-gap Fabry-Perot (F-P) interferometric imaging spectrometer, whether the spatial interference information is sampled at equal intervals of optical path difference (OPD), that is, whether the relationship between optical path difference and detector pixel position is linear, directly determines the difficulty of spectral data processing . After analysis, the OPD of the variable-gap F-P interferometric imaging system was the function of the centre distance of two Airy disks produced by the beam split of the interferometer. However, the centre distance of two Airy disks did not always maintain a linear relationship with the detector pixel position, which was related to the value of the wedge angle of the interferometer. The relationship between optical path difference and detector pixel position under different wedge angle conditions was studied. The results show that there is a good linear relationship between optical path difference and detector array pixel position at any wedge angle, and the position contact ratio of characteristic peak measured by long wave infrared spectral imaging system with variable-gap F-P interference and spectral radiometer with high precision reaches to 100%.
The divergence angle is an important measurement index of the beam characteristics of terahertz sources and an important parameter in the design of terahertz optical system. The measurement principle of terahertz source divergence angle was studied, the measuring device was designed, which was composed of precise arc guide rail, chopper, narrow slit components, terahertz Golay detector, lock-in amplifier and computer system. And the calibration module of divergence angle measuring device was also designed, which included auto-collimator, optical angle gauges and CCD camera. And then, the divergence angle of terahertz Schottky frequency doubling source and the terahertz avalanche solid state source were measured. In addition, the uncertainty of measurement results was evaluated, and the uncertainty level reaches to
In order to realize the fast nondestructive identification of blended gasoline, an identification method based on t-distributed stochastic neighborhood embedding(t-SNT) combined with deep belief networks was proposed to solve the nonlinear relationship between high-dimensional feature vectors in machine learning. Taking 92#, 95#, 98# and fixed ratio blended gasoline as the research objects, the projection spectrum measurement data in original infrared band was preprocessed by multivariate scattering correction algorithm, and the dimension reduction of spectral data was carried out by using t-SNE nonlinear method. The spectral identification model of gasoline types was established by using deep belief networks and extreme learning machine respectively, and the identification accuracy of the two methods was compared and analyzed. The research shows that the gasoline identification model constructed by this method has better performance, and the prediction accuracy of gasoline types is as high as 92.5%, which verifies the effectiveness of this method in gasoline identification. The results of this research can provide technical support for the identification and traceability of blending refined oil products.
The strapdown inertial navigation system is generally used for photoelectric target calibration. The inertial navigation axis should be characterized by the photoelectric auto-collimation system for the measurement of the equipment axis. The consistency between the axis characterized by the photoelectric auto-collimation system and the inertial navigation axis is an important factor affecting the target calibration accuracy. In order to improve the measurement accuracy and efficiency of the photoelectric target calibration system, a photoelectric characterization and calibration method of the inertial navigation axis was proposed. This method was based on the analysis of the relationship between the deviation and consistency of the measurement results, and the angle deviation value between the auto-collimation system optical axis and the inertial navigation axis was obtained by fitting the experimental data, which was used for the system correction, so as to realize the high-precision calibration. Through the test, by combining the traditional optical machine correction method with the photoelectric calibration method, the calibration efficiency of the system could be greatly improved, and the consistency accuracy between the inertial navigation axis and the optical axis was less than 15″ at the same time. The experimental results show that compared with the traditional optical machine correction method by the traditional optical flat-crystal, the proposed method has higher characterization accuracy and calibration accuracy, which is suitable for high-precision inertial measurement system.
The traditional dynamic light scattering method usually collects the lateral scattering to measure the size distribution of nano-particles. Because of the influence of multiple scattering, the particle size distribution of high-concentration samples cannot be accurately measured by lateral scattering. Aiming at the problem, the back scattering measurement method was studied, and the criterion of the optimal optical path of back scattering was proposed based on the experiment. At different sample concentrations, the polystyrene latex sphere particles with a nominal particle size of 110 nm and 220 nm were measured by lateral scattering method and back scattering method, respectively. The experimental results show that the back scattering method can self-adaptively adjust the optical path for high-concentration samples, and the measurement can be carried out at the optimal optical path to effectively obtain the particle size and the size distribution of high-concentration nano-particles, and the relative error of measurement results is 2.72%.
The binocular cloud height observation system has a long baseline, so it is difficult to calibrate the external parameters of the system. An external parameter calibration method for binocular camera used in ground-based cloud height measurement system was proposed. The oriented FAST and rotated BRIEF (ORB) algorithm was used to extracte the left and right cloud image points with the same name for matching, and then calculate the rotation and translation relationship between two cameras according to the antipode geometric constraints. In order to verify the accuracy of the algorithm, a binocular cloud height system with a baseline of 60 m was set up outdoors. The odometer method was used to calibrate the external parameters, and the distance error between two cameras was 34.44 cm, the accuracy was 99.43%. Finally, by analyzing the corrected binocular cloud image and sky parallax image, the higher accuracy of the external parameter calibration method of the large baseline odometer was verified.
The laser developed atmospheric lens (LDAL) is an advanced concept of space surveillance, that is, the high-energy laser was used to form a lens-like structure in the atmosphere to achieve the effective surveillance of enemy targets. The application requirements of this concept were introduced, and the generation mechanism and system structure of laser developed atmospheric lens were analyzed in detail. The technical challenges it faces were discussed in depth, which included the formation effect, moulding method, required laser power, airborne power, target surveillance time and so on, and the relevant information was analyzed. The analysis results show that the laser developed atmospheric lens is an overturning emerging technology, which may change the battlefield perception situation in the future. Technologies such as the miniaturization of high-power laser, huge airborne power, high-speed photography, adaptive optics and high-precision imaging are needed for realization.
The damage experiment of 416 nm nanosecond pulsed laser to charge-coupled device (CCD) was carried out. The process from point damage to line damage and then to surface damage was observed. The damage energy density thresholds corresponding to point damage, line damage and surface damage were calculated to be 16.7 mJ/cm2~71.9 mJ/cm2, 61.0 mJ/cm2~207.8 mJ/cm2 and 352.6 mJ/cm2, respectively. Through analyzing the microscopic images of the damage point surface of CCD in different damage states and measuring the resistance values between CCD electrodes corresponding to different damage states, it was concluded that the different damage states were mainly caused by the different changes of resistance values caused by the phase change of silicon dioxide insulating layer material. Through simulation of COMSOL software, it was concluded that the silicon dioxide insulating layer was the first layer to melt in each layer of CCD, and the energy density was 420 mJ/cm2, which was close to the experimental results and proved the correctness of the analysis of CCD damage mechanism.
The laser anti-satellite weapons are important means of jamming and destroying space-borne photoelectric instruments or destroying satellite platforms. Based on the Fourier unsteady state heat conduction equation, combined with actual structure inside the target and high temperature characteristics of the metal material, the simulation process of satellite cylinder damage under laser irradiation was realized through the modeling and numerical simulation, and the multi-physical change laws such as temperature, melting depth and internal stress distribution of the target under typical operating conditions were obtained. The effects of lasers with different power densities on the temperature field and melting rate of the target and the stress coupling phenomenon inside the target were analyzed. The results show that as the laser power density continues to increase, the damage rate of the target increases, but its melting rate tends to be stable at the phase transition. At the same time, under typical conditions, due to the stress coupling effect, the target will exceed the allowable stress value in a very short time, and the damage occurs.
Taking space attack and defense as the application background, the active and passive space-based laser detection technology was deeply researched. The related situations of research on LIDAR and laser warning in space-based platform at home and abroad were briefly described. On this basis, the framework design of active and passive laser detection technology based on space-based platform was developed, the components and their functions were discussed, and the involved key technologies such as laser transmitting-receiving, light beam scanning, laser warning were deeply analyzed.
As a micro-nano machining method, the focused ion beam (FIB) processing can be used to manufacture the nanometer elements and microstructure elements. The whole process of designing and manufacturing the 45° mirror surface at the end of multi-core fiber using focused ion beam processing technology was studied. This mirror surface was manufactured in two steps: the first was the scanning process, which was used to manufacture the rough cut surface; the second was the polishing process, which was used for the surface finish of optical surface. The machined 45˚ mirror surface could be accurately aligned with the fibre core of optical fiber, which avoided related issues of external turning mirror components docking. The experimental test show that the displacement value in two vertical axial directions can be measured by the machined structure with interferometry. The measuring range of the detection displacement is approximately 60 µm, and the absolute measurement error of root-mean-square in X and Y axial directions is 1.75‰ and 1.97‰, respectively. This technology is expected to be used in the detection fields of inner surface and vessels inter wall for precision components.
A passively mode-locked fiber laser based on nonlinear polarization rotation mechanism was reported. The 980 nm distributed feedback laser was used as the pump source and the highly doped erbium-doped fiber with length of 0.5 m was used as the gain medium. The traditional soliton mode-locked pulse with the pulse width of 822 fs was realized, the average power of the output pulse was 2.8 mW, and the signal-to-noise ratio (SNR) was 55.8 dB. By adjusting the polarization controller slightly in the cavity, the switch between traditional soliton pulse and soliton molecule pulse was realized, the pulse width and the SNR of the soliton molecule were 312 fs and 53.86 dB, respectively. The soliton molecule pulse was amplified by the erbium-doped fiber amplifier to pump a 57 m long high nonlinear fiber, which produced a super-continuum spectrum located in the third near-infrared window (1 600 nm~1 870 nm) with a 20 dB spectrum width of 355.8 nm.