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RSS2022 Vol. 46, No. 2
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2022, 46(2): 149-154.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.001
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Abstract:
In order to explore the feasibility of using conventional fiber to fabricate weak fiber Bragg grating (WFBG) and reduce the material cost and transmission loss, a WFBG was fabricated on a conventional single-mode fiber (CSMF) based on phase mask method. The unified optical field equation of phase mask grating system was established, and the influence of optical field distribution on center wavelength and reflectivity of FBG was analyzed. The influence of phase mask length and average change of refractive index on reflectivity and 3dB bandwidth of FBG was analyzed by transfer matrix method, which provides theoretical basis for improving WFBG lithography. WFBGs were fabricated on CSMFs by 248nm UV excimer laser. The effects of phase mask length, exposure energy, exposure frequency, and exposure times on central wavelength, reflectivity, and 3dB bandwidth of WFBG were respectively analyzed. Two kinds of WFBGs with narrow and wide bandwidths were fabricated with reflectivity and 3dB bandwidth of 0.0016 and 0.10nm, 0.00006 and 0.34nm, respectively. Theoretical and experimental results show that WFBG can be fabricated on CSMF stably by the multi-pulse exposure of UV excimer laser based on the phase mask method, which provides a reference for the material selection of the weak reflection fiber grating.
In order to explore the feasibility of using conventional fiber to fabricate weak fiber Bragg grating (WFBG) and reduce the material cost and transmission loss, a WFBG was fabricated on a conventional single-mode fiber (CSMF) based on phase mask method. The unified optical field equation of phase mask grating system was established, and the influence of optical field distribution on center wavelength and reflectivity of FBG was analyzed. The influence of phase mask length and average change of refractive index on reflectivity and 3dB bandwidth of FBG was analyzed by transfer matrix method, which provides theoretical basis for improving WFBG lithography. WFBGs were fabricated on CSMFs by 248nm UV excimer laser. The effects of phase mask length, exposure energy, exposure frequency, and exposure times on central wavelength, reflectivity, and 3dB bandwidth of WFBG were respectively analyzed. Two kinds of WFBGs with narrow and wide bandwidths were fabricated with reflectivity and 3dB bandwidth of 0.0016 and 0.10nm, 0.00006 and 0.34nm, respectively. Theoretical and experimental results show that WFBG can be fabricated on CSMF stably by the multi-pulse exposure of UV excimer laser based on the phase mask method, which provides a reference for the material selection of the weak reflection fiber grating.
2022, 46(2): 155-162.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.002
Abstract:
With the development of optical communication and optical networks, the ability to control chromatic dispersion is paramount in optical applications. Several new methods of dispersion generation were introduced and their principles, developments, advantages, and disadvantages were discussed, including the dispersion system based on modal dispersion, electromagnetically induced transparency (EIT) and the dispersion system based the real-time Fourier transform(RTFT) to generate equivalent dispersion. The general difficulties of the dispersion generation technology were analyzed and the development trend of it was discussed. By introducing the technology of dispersion generation, its application prospects for optical information processing were discussed.
With the development of optical communication and optical networks, the ability to control chromatic dispersion is paramount in optical applications. Several new methods of dispersion generation were introduced and their principles, developments, advantages, and disadvantages were discussed, including the dispersion system based on modal dispersion, electromagnetically induced transparency (EIT) and the dispersion system based the real-time Fourier transform(RTFT) to generate equivalent dispersion. The general difficulties of the dispersion generation technology were analyzed and the development trend of it was discussed. By introducing the technology of dispersion generation, its application prospects for optical information processing were discussed.
2022, 46(2): 163-168.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.003
Abstract:
To improve the catalytic effect of titanium dioxide under solar light, a silver film was deposited on the titanium surface by the vacuum evaporation method, and a femtosecond laser was used for the fabrication of the micro/nanostructured titanium dioxide and the incorporation of silver particles simultaneously. The results show that the photocatalytic efficiency of the Ag-TiO2 for removal of methylene blue is as high as 70% under simulated sunlight for 300min, which is 1.5 times of the photocatalytic efficiency of structured TiO2. This method based on direct processing of bulk materials can increase the specific surface area and solve the problems of traditional titanium dioxide's recycling. Therefore, this technology shows high potential in the fabrication of environment-friendly titanium dioxide photocatalyst with high efficiency and large-scale and rapid production in factories.
To improve the catalytic effect of titanium dioxide under solar light, a silver film was deposited on the titanium surface by the vacuum evaporation method, and a femtosecond laser was used for the fabrication of the micro/nanostructured titanium dioxide and the incorporation of silver particles simultaneously. The results show that the photocatalytic efficiency of the Ag-TiO2 for removal of methylene blue is as high as 70% under simulated sunlight for 300min, which is 1.5 times of the photocatalytic efficiency of structured TiO2. This method based on direct processing of bulk materials can increase the specific surface area and solve the problems of traditional titanium dioxide's recycling. Therefore, this technology shows high potential in the fabrication of environment-friendly titanium dioxide photocatalyst with high efficiency and large-scale and rapid production in factories.
2022, 46(2): 169-174.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.004
Abstract:
In order to improve the endurance of the micro-unmanned aerial vehicle (MUAV), based on the working principle of the two-axis scanning galvanometer, a remote real-time laser tracking and pointing charging system for the MUAV was designed. In the system, a silicon photocell array was used as the spot position sensor. Firstly, the signal was processed through a scanning tracking algorithm, then a wireless data transmission feedback link was established between the ground and the MUAV, and the emission direction of a laser beam could be changed by controlling the two-axis scanning galvanometer. At the same time, the silicon photocell array was also used as a charging device to realize real-time charging of MUAV. The experimental test results show that when the MUAV flies at a speed of less than 2m/s in a circular area with a height of 80m and a diameter of 50m, the system can accurately track the MUAV with a tracking accuracy of less than 0.63mrad. It has the characteristics of fast tracking speed and high aiming accuracy. This research provides an effective solution for laser remote real-time energy transmission to moving targets.
In order to improve the endurance of the micro-unmanned aerial vehicle (MUAV), based on the working principle of the two-axis scanning galvanometer, a remote real-time laser tracking and pointing charging system for the MUAV was designed. In the system, a silicon photocell array was used as the spot position sensor. Firstly, the signal was processed through a scanning tracking algorithm, then a wireless data transmission feedback link was established between the ground and the MUAV, and the emission direction of a laser beam could be changed by controlling the two-axis scanning galvanometer. At the same time, the silicon photocell array was also used as a charging device to realize real-time charging of MUAV. The experimental test results show that when the MUAV flies at a speed of less than 2m/s in a circular area with a height of 80m and a diameter of 50m, the system can accurately track the MUAV with a tracking accuracy of less than 0.63mrad. It has the characteristics of fast tracking speed and high aiming accuracy. This research provides an effective solution for laser remote real-time energy transmission to moving targets.
2022, 46(2): 175-181.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.005
Abstract:
As one of the important devices in smart grid, all fiber optic current sensor has more significant advantages than traditional electromagnetic transformer, and has broad application prospects in high voltage and ultra-high voltage environment. Firstly, the main factors affecting the sensitivity of all fiber optic current sensor are clarified, and the solutions and research results for improving the sensitivity of current sensor by domestic and foreign scholars in recent years are summarized; Secondly, the working principle of some improved all fiber optic current sensors to eliminate the influence of temperature and linear birefringence on the sensing sensitivity is emphatically analyzed, and their main advantages and disadvantages are discussed; Finally, combined with the research status of high sensitivity all fiber current sensor, the future development trend is pointed out.
As one of the important devices in smart grid, all fiber optic current sensor has more significant advantages than traditional electromagnetic transformer, and has broad application prospects in high voltage and ultra-high voltage environment. Firstly, the main factors affecting the sensitivity of all fiber optic current sensor are clarified, and the solutions and research results for improving the sensitivity of current sensor by domestic and foreign scholars in recent years are summarized; Secondly, the working principle of some improved all fiber optic current sensors to eliminate the influence of temperature and linear birefringence on the sensing sensitivity is emphatically analyzed, and their main advantages and disadvantages are discussed; Finally, combined with the research status of high sensitivity all fiber current sensor, the future development trend is pointed out.
2022, 46(2): 182-187.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.006
Abstract:
In order to study the effect of pulse energy and ablation crater overlap rate on the bonding strength of 7075-T6 aluminum substrate, a nanosecond fiber pulse laser was used to process the ablation crater array microstructure in the bonding area, and the bonding effect was analyzed based on the surface morphology, shear strength and fracture mode. The results show that the pulse energy has almost no effect on the surface morphology, shear strength, and fracture mode. As the overlap rate of ablation crater increases, the surface roughness first increases and then decreases, while the developed interfacial area ratio keeps increasing. Compared with the original material, the shear strength after laser treatment is increased by at least 150%. When the ablation crater overlap rate is 30%, the largest cohesive fracture area of the bonding area is obtained, and the most significant increasement of the shear strength is observed. When the pulse energy is 880μJ and the ablation crater overlap rate is 30%, the shear strength is 27.76MPa, which is the largest increasement. This study is helpful for improving the bonding strength of 7075-T6 by laser ablation.
In order to study the effect of pulse energy and ablation crater overlap rate on the bonding strength of 7075-T6 aluminum substrate, a nanosecond fiber pulse laser was used to process the ablation crater array microstructure in the bonding area, and the bonding effect was analyzed based on the surface morphology, shear strength and fracture mode. The results show that the pulse energy has almost no effect on the surface morphology, shear strength, and fracture mode. As the overlap rate of ablation crater increases, the surface roughness first increases and then decreases, while the developed interfacial area ratio keeps increasing. Compared with the original material, the shear strength after laser treatment is increased by at least 150%. When the ablation crater overlap rate is 30%, the largest cohesive fracture area of the bonding area is obtained, and the most significant increasement of the shear strength is observed. When the pulse energy is 880μJ and the ablation crater overlap rate is 30%, the shear strength is 27.76MPa, which is the largest increasement. This study is helpful for improving the bonding strength of 7075-T6 by laser ablation.
2022, 46(2): 188-192.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.007
Abstract:
In order to implement the large beam pointing range and the fine step adjustment of an optical beamforming network (OBFN), a method of optical dispersion-based optical true time delay (OTTD) was adopted. The path switching of N-way high dispersion fiber was realized by the optical switch, and thus the equally large-step delay difference was realized, then the beam pointing with a large range and a stride adjustment was realized. By tuning the dispersion coefficient of the linear chirped fiber Bragg grating (LCFBG), the equally small-step delay difference was realized, and then beam pointing with a small range and a small-step adjustment was realized. The theoretical analysis and simulation verification of the above method were carried out, and a beam pointing angle range of -73.74°~+73.74° and a switching step of 0.458° was obtained. The result shows that the large beam pointing range and the fine step adjustment of the OBFN were realized based on optical dispersion, which is helpful to improve the system designing of phased-array antenna.
In order to implement the large beam pointing range and the fine step adjustment of an optical beamforming network (OBFN), a method of optical dispersion-based optical true time delay (OTTD) was adopted. The path switching of N-way high dispersion fiber was realized by the optical switch, and thus the equally large-step delay difference was realized, then the beam pointing with a large range and a stride adjustment was realized. By tuning the dispersion coefficient of the linear chirped fiber Bragg grating (LCFBG), the equally small-step delay difference was realized, and then beam pointing with a small range and a small-step adjustment was realized. The theoretical analysis and simulation verification of the above method were carried out, and a beam pointing angle range of -73.74°~+73.74° and a switching step of 0.458° was obtained. The result shows that the large beam pointing range and the fine step adjustment of the OBFN were realized based on optical dispersion, which is helpful to improve the system designing of phased-array antenna.
2022, 46(2): 193-198.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.008
Abstract:
In order to study the influence of different laser power on swing welding steel/aluminum, the lap experiments of DP780 dual-phase steel and 5083 aluminum alloy were carried out by combining a high-power disc laser with a swing joint of PFO3D. The experimental results show that the plate welding can be effectively realized within the power range of 1400W~1600W. When the laser power is 1400W, the microstructure of the welded joint is low carbon martensite, and the lowest and highest microhardness are located in the heat affected zone and the weld center, respectively. With the increase of laser power, the amount of ferrite in the weld increases, while the amount of martensite decreases. The maximum and minimum values of microhardness of the joint are changed to heat affected zone and weld center, respectively. When the laser power is 1400W, the tensile strength of the weld is the highest, which is 2681MPa. The research results are of great significance in the field of shipbuilding.
In order to study the influence of different laser power on swing welding steel/aluminum, the lap experiments of DP780 dual-phase steel and 5083 aluminum alloy were carried out by combining a high-power disc laser with a swing joint of PFO3D. The experimental results show that the plate welding can be effectively realized within the power range of 1400W~1600W. When the laser power is 1400W, the microstructure of the welded joint is low carbon martensite, and the lowest and highest microhardness are located in the heat affected zone and the weld center, respectively. With the increase of laser power, the amount of ferrite in the weld increases, while the amount of martensite decreases. The maximum and minimum values of microhardness of the joint are changed to heat affected zone and weld center, respectively. When the laser power is 1400W, the tensile strength of the weld is the highest, which is 2681MPa. The research results are of great significance in the field of shipbuilding.
2022, 46(2): 199-205.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.009
Abstract:
To overcome the shortcomings of the classic collaborative sparse unmixing algorithm and the edge blur problem caused by the total variation regular term, considering the importance of sparsity and spatial information to improve the accuracy of unmixing, a novel algorithm called superpixel and low rank for collaborative sparse unmixing was proposed. The unmixing algorithm was theoretically analyzed and experimentally verified. The superpixel segmentation was performed on the hyperspectral images, and then collaborative sparsity constraints were imposed on each superpixel. In addition, a low-rank regular term was used instead of the traditional total variation regular term to utilize spatial information. A set of simulated data and a set of real data were selected for experiments. These results show that the signal reconstruction error obtained in the simulated experiment is 19.4 when the signal-to-noise ratio is 30dB, which is about 35% higher than that of the classic sparse unmixing via variable splitting augmented Lagrangian and total variation algorithm. Real data experiment intuitively reflects that the algorithm can effectively overcome the problem of edge blur. The proposed algorithm has better unmixing performance. This research provides a reference for how to use sparsity and spatial information comprehensively.
To overcome the shortcomings of the classic collaborative sparse unmixing algorithm and the edge blur problem caused by the total variation regular term, considering the importance of sparsity and spatial information to improve the accuracy of unmixing, a novel algorithm called superpixel and low rank for collaborative sparse unmixing was proposed. The unmixing algorithm was theoretically analyzed and experimentally verified. The superpixel segmentation was performed on the hyperspectral images, and then collaborative sparsity constraints were imposed on each superpixel. In addition, a low-rank regular term was used instead of the traditional total variation regular term to utilize spatial information. A set of simulated data and a set of real data were selected for experiments. These results show that the signal reconstruction error obtained in the simulated experiment is 19.4 when the signal-to-noise ratio is 30dB, which is about 35% higher than that of the classic sparse unmixing via variable splitting augmented Lagrangian and total variation algorithm. Real data experiment intuitively reflects that the algorithm can effectively overcome the problem of edge blur. The proposed algorithm has better unmixing performance. This research provides a reference for how to use sparsity and spatial information comprehensively.
2022, 46(2): 206-212.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.010
Abstract:
Low-level wind shear is a major threat to aviation safety. To study the fine structure and evolution of typical low-level wind shear in plateau airports, for the two types of wind shear caused by different synoptic processes at Xining Airport on 2020-02-13, FC-Ⅲ wind lidar data combined with wind profile radar and other data were anaylized. The results show that the causes and evolution characteristics of the two types of wind shear are different, the tailwind shear line exhibits as a "cone" and affects the runway from west to east, while the moving path of the headwind shear line is opposite, the maximum wind speed exceeds 20m/s. The vertical structure of the wind field has different characteristics, the wind speed of more than 15m/s propagates downwards causing tailwind shear; for the headwind shear, wind direction changes over 160° in the near-surface layer; in the two processes, wind speed difference between adjacent moments in the glide path mode both exceed 15m/s. The formation and development of the two types of low-level wind shear in the plateau winter are rapid. The high-resolution three-dimensional scanning lidar can detect the evolution process and fine structure of the wind shear, which is significant to improving aviation safety.
Low-level wind shear is a major threat to aviation safety. To study the fine structure and evolution of typical low-level wind shear in plateau airports, for the two types of wind shear caused by different synoptic processes at Xining Airport on 2020-02-13, FC-Ⅲ wind lidar data combined with wind profile radar and other data were anaylized. The results show that the causes and evolution characteristics of the two types of wind shear are different, the tailwind shear line exhibits as a "cone" and affects the runway from west to east, while the moving path of the headwind shear line is opposite, the maximum wind speed exceeds 20m/s. The vertical structure of the wind field has different characteristics, the wind speed of more than 15m/s propagates downwards causing tailwind shear; for the headwind shear, wind direction changes over 160° in the near-surface layer; in the two processes, wind speed difference between adjacent moments in the glide path mode both exceed 15m/s. The formation and development of the two types of low-level wind shear in the plateau winter are rapid. The high-resolution three-dimensional scanning lidar can detect the evolution process and fine structure of the wind shear, which is significant to improving aviation safety.
2022, 46(2): 213-219.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.011
Abstract:
In order to solve the distortion of the demodulated signal caused by the drift of modulation depth in the traditional phase generation carrier demodulation algorithms, the signal demodulation method of differential cross division was adopted. Related theoretical analysis and simulation verification were carried out, and a high-performance phase-generating carrier demodulation scheme that was not limited by the modulation depth was obtained. The results show that the demodulation performance of the improved algorithm is always excellent when the signals under test of different amplitudes and frequencies are used for simulation. When the values of modulation depth are respectively typical values such as 2.63rad and 2.37rad and atypical values such as 1.5rad and 3.0rad, the demodulated signals obtained by improved algorithm has no distortion. At the same time, when the modulation depth changes in the range of 0.5rad~3.5rad, compared with traditional demodulation algorithms, the amplitude of the demodulated signal in the improved algorithm is always consistent with the signal under test and the high-order harmonic components are always very small. This research solves the distortion phenomenon caused by the modulation depth change in traditional demodulation algorithms, and provides a reference for the demodulation scheme of the optical fiber interferometric sensor system.
In order to solve the distortion of the demodulated signal caused by the drift of modulation depth in the traditional phase generation carrier demodulation algorithms, the signal demodulation method of differential cross division was adopted. Related theoretical analysis and simulation verification were carried out, and a high-performance phase-generating carrier demodulation scheme that was not limited by the modulation depth was obtained. The results show that the demodulation performance of the improved algorithm is always excellent when the signals under test of different amplitudes and frequencies are used for simulation. When the values of modulation depth are respectively typical values such as 2.63rad and 2.37rad and atypical values such as 1.5rad and 3.0rad, the demodulated signals obtained by improved algorithm has no distortion. At the same time, when the modulation depth changes in the range of 0.5rad~3.5rad, compared with traditional demodulation algorithms, the amplitude of the demodulated signal in the improved algorithm is always consistent with the signal under test and the high-order harmonic components are always very small. This research solves the distortion phenomenon caused by the modulation depth change in traditional demodulation algorithms, and provides a reference for the demodulation scheme of the optical fiber interferometric sensor system.
2022, 46(2): 220-225.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.012
Abstract:
In order to identify the number of maize plants without damage, the four station scanning method was used to collect the data of corn field point cloud from different perspectives by using FARO focus s70 laser scanner. A registration algorithm based on automatic extraction of target ball was designed. The point cloud data obtained by each station was accurately registered, and the complete corn field point cloud data was obtained. The registration accuracy was analyzed by the fitting error and standard deviation of the target ball. For the three-dimensional point cloud data, the stem point cloud was separated from the whole corn field point cloud by using the sampling consistency algorithm based on the cylinder characteristics, and the number of corn planting plants was counted. The results show that the standard deviation of the standard fitting of the target ball is between 0.1mm and 0.7mm, which meets the requirements of the instrument measurement accuracy. The fitting error is between 2mm~5mm, which can meet the requirements of 5mm in large scene measurement registration error. The recognition rate of maize plant number was 86.1%~92.1%. This result is helpful to the practical application of maize plant number identification in farmland environment, providing data base for crop yield estimation and theoretical method for intelligent agricultural research.
In order to identify the number of maize plants without damage, the four station scanning method was used to collect the data of corn field point cloud from different perspectives by using FARO focus s70 laser scanner. A registration algorithm based on automatic extraction of target ball was designed. The point cloud data obtained by each station was accurately registered, and the complete corn field point cloud data was obtained. The registration accuracy was analyzed by the fitting error and standard deviation of the target ball. For the three-dimensional point cloud data, the stem point cloud was separated from the whole corn field point cloud by using the sampling consistency algorithm based on the cylinder characteristics, and the number of corn planting plants was counted. The results show that the standard deviation of the standard fitting of the target ball is between 0.1mm and 0.7mm, which meets the requirements of the instrument measurement accuracy. The fitting error is between 2mm~5mm, which can meet the requirements of 5mm in large scene measurement registration error. The recognition rate of maize plant number was 86.1%~92.1%. This result is helpful to the practical application of maize plant number identification in farmland environment, providing data base for crop yield estimation and theoretical method for intelligent agricultural research.
2022, 46(2): 226-232.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.013
Abstract:
In order to study the temperature field distribution of single-channel laser cladding sheet, a Gaussian heat source model was used to simulate the energy of laser beam through ANSYS software, and the temperature field of single-channel laser cladding and cooling process was simulated by using nonlinear boundary setting. A 2kW fiber laser was used to cladding iron based (Fe60) powder onto a 2mm thick T9A steel plate, and the temperature at various points was measured by a thermal imager. The results show that the simulation results of temperature field of laser cladding sheet accord with the experimental results, and the maximum error of its maximum temperature is 8.31%.The research results are useful for the optimization of laser machining parameters.
In order to study the temperature field distribution of single-channel laser cladding sheet, a Gaussian heat source model was used to simulate the energy of laser beam through ANSYS software, and the temperature field of single-channel laser cladding and cooling process was simulated by using nonlinear boundary setting. A 2kW fiber laser was used to cladding iron based (Fe60) powder onto a 2mm thick T9A steel plate, and the temperature at various points was measured by a thermal imager. The results show that the simulation results of temperature field of laser cladding sheet accord with the experimental results, and the maximum error of its maximum temperature is 8.31%.The research results are useful for the optimization of laser machining parameters.
2022, 46(2): 233-238.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.014
Abstract:
In order to solve the problems such as single feature, low calculation efficiency, and poor effect of vegetation coverage of the current airborne light detection and ranging(LiDAR) point cloud filtering algorithm, an adaptive double filtering method for point cloud in densely-vegetated areas was proposed. Firstly, the single and last echo of point cloud were extracted respectively and processed by coarse filtering by using the echo separation method. Then, the skewness balance theory was used to determine the intensity threshold of the single echo, and the maximum inter-class variance method was used to calculate the height difference between the first echo and the last echo, so as to realize the automation of the height difference threshold of the last echo. And the point cloud data of the single echo and the last echo after rough filtering were integrated. Finally, the incremental encryption filtering algorithm of triangulated irregular network was used to carry out the fine filtering processing on the fused point cloud data, and the experimental verification had been done. The results show that the type Ⅱ errors of the three data sets are relatively low of 1.06%, 1.64%, and 1.34% respectively. The dual filtering method that combines echo information and height difference information can not only eliminate vegetation, but also retain terrain details.
In order to solve the problems such as single feature, low calculation efficiency, and poor effect of vegetation coverage of the current airborne light detection and ranging(LiDAR) point cloud filtering algorithm, an adaptive double filtering method for point cloud in densely-vegetated areas was proposed. Firstly, the single and last echo of point cloud were extracted respectively and processed by coarse filtering by using the echo separation method. Then, the skewness balance theory was used to determine the intensity threshold of the single echo, and the maximum inter-class variance method was used to calculate the height difference between the first echo and the last echo, so as to realize the automation of the height difference threshold of the last echo. And the point cloud data of the single echo and the last echo after rough filtering were integrated. Finally, the incremental encryption filtering algorithm of triangulated irregular network was used to carry out the fine filtering processing on the fused point cloud data, and the experimental verification had been done. The results show that the type Ⅱ errors of the three data sets are relatively low of 1.06%, 1.64%, and 1.34% respectively. The dual filtering method that combines echo information and height difference information can not only eliminate vegetation, but also retain terrain details.
2022, 46(2): 239-247.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.015
Abstract:
In order to reduce the amount of feature extraction network parameters and computation of effective convolution operator (ECO) tracking algorithm, the improved eco target tracking algorithm based on GhostNet was adopted. Firstly, the GhostNet network was used as the main feature extraction network to extract the convolution features of shallow and deep layers, and the global average pooling was adapted to downsampling convolution features to improve the image representation ability. Secondly, after interpolating the convolution feature with the manual feature, convolution calculation was performed with the current filter in the Fourier domain to realize the target localization. Finally, conjugate gradient algorithm was used to optimize the loss function of the sum of response error and penalty term to update the filter. Theoretical analysis and experimental verification were carried out on the proposed algorithm and OTB2015 and VOT2018 datasets, then the comparative experimental data of target tracking were obtained. The results show that compared with the ECO algorithm based on ResNet feature extraction network, the proposed algorithm can achieve higher precision tracking, the convolution feature extraction process reduces 95.75% of computation and 79.69% of parameters, and the tracking speed increases 160% at the same time. These results provide a reference for the research of lightweight target tracking algorithms.
In order to reduce the amount of feature extraction network parameters and computation of effective convolution operator (ECO) tracking algorithm, the improved eco target tracking algorithm based on GhostNet was adopted. Firstly, the GhostNet network was used as the main feature extraction network to extract the convolution features of shallow and deep layers, and the global average pooling was adapted to downsampling convolution features to improve the image representation ability. Secondly, after interpolating the convolution feature with the manual feature, convolution calculation was performed with the current filter in the Fourier domain to realize the target localization. Finally, conjugate gradient algorithm was used to optimize the loss function of the sum of response error and penalty term to update the filter. Theoretical analysis and experimental verification were carried out on the proposed algorithm and OTB2015 and VOT2018 datasets, then the comparative experimental data of target tracking were obtained. The results show that compared with the ECO algorithm based on ResNet feature extraction network, the proposed algorithm can achieve higher precision tracking, the convolution feature extraction process reduces 95.75% of computation and 79.69% of parameters, and the tracking speed increases 160% at the same time. These results provide a reference for the research of lightweight target tracking algorithms.
2022, 46(2): 248-253.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.016
Abstract:
In order to solve the problem that acoustic monitoring method of laser cleaning is difficult to be practically applied, the Bayesian discriminant method was used to conduct theoretical analysis and experimental verification. The paint removal process was divided into three categories: cleaning, cleaning completed and no damage to the substrate, and damage to the substrate. Combining the photoacoustic effect, the change of the paint removal sound signal during the cleaning process was analyzed, the characteristic parameters were extraced to establish a discriminant model. The accuracy of training samples reaches 99%, and the accuracy of test samples reaches 98.7%. The results show that the method has high accuracy and practicability. It can provide a reference for the research of laser cleaning acoustic monitoring.
In order to solve the problem that acoustic monitoring method of laser cleaning is difficult to be practically applied, the Bayesian discriminant method was used to conduct theoretical analysis and experimental verification. The paint removal process was divided into three categories: cleaning, cleaning completed and no damage to the substrate, and damage to the substrate. Combining the photoacoustic effect, the change of the paint removal sound signal during the cleaning process was analyzed, the characteristic parameters were extraced to establish a discriminant model. The accuracy of training samples reaches 99%, and the accuracy of test samples reaches 98.7%. The results show that the method has high accuracy and practicability. It can provide a reference for the research of laser cleaning acoustic monitoring.
2022, 46(2): 254-259.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.017
Abstract:
To improve the real-time performance of distributed optical fiber sensing system based on Brillouin scattering, through the analysis of the strengths and weaknesses of the classical Lorentzian and pseudo-Voigt models fitting methods, the multi-layer feedforward artificial neural network (ANN) method was used to estimate the Brillouin frequency shift. The structure, input and output, activation function, and training algorithm of the ANN were determined. The ANN was trained by simulated Brillouin spectra with different signal-to-noise ratios (5dB~40dB) and Brillouin frequency shifts (10.62GHz~10.82GHz). The Brillouin frequency shift estimation error of the trained ANN for the training samples was only about 1MHz. At the same time, the radial basis function ANN was also trained. For the Brillouin spectra with temperature and strain varied along the optical fiber, the trained multi-layer feedforward ANN and radial basis function ANN, the spectrum fitting methods based on the Lorentzian model and the pseudo-Voigt model were respectively used to estimate the Brillouin frequency shift along the optical fiber, and at the same time the temperature and strain along the optical fiber were obtained by demodulation. The results show that the accuracy of the multi-layer feedforward ANN method is similar to that of the classical spectral fitting method based on the Lorentzian and pseudo-Voigt models, but the calculation time is only 1/947.16~1/470.95 and 1/784.56~1/532.88 of the latter two. This work provides a reference for the rapid measurement of optical fiber temperature and strain based on Brillouin scattering.
To improve the real-time performance of distributed optical fiber sensing system based on Brillouin scattering, through the analysis of the strengths and weaknesses of the classical Lorentzian and pseudo-Voigt models fitting methods, the multi-layer feedforward artificial neural network (ANN) method was used to estimate the Brillouin frequency shift. The structure, input and output, activation function, and training algorithm of the ANN were determined. The ANN was trained by simulated Brillouin spectra with different signal-to-noise ratios (5dB~40dB) and Brillouin frequency shifts (10.62GHz~10.82GHz). The Brillouin frequency shift estimation error of the trained ANN for the training samples was only about 1MHz. At the same time, the radial basis function ANN was also trained. For the Brillouin spectra with temperature and strain varied along the optical fiber, the trained multi-layer feedforward ANN and radial basis function ANN, the spectrum fitting methods based on the Lorentzian model and the pseudo-Voigt model were respectively used to estimate the Brillouin frequency shift along the optical fiber, and at the same time the temperature and strain along the optical fiber were obtained by demodulation. The results show that the accuracy of the multi-layer feedforward ANN method is similar to that of the classical spectral fitting method based on the Lorentzian and pseudo-Voigt models, but the calculation time is only 1/947.16~1/470.95 and 1/784.56~1/532.88 of the latter two. This work provides a reference for the rapid measurement of optical fiber temperature and strain based on Brillouin scattering.
2022, 46(2): 260-266.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.018
Abstract:
In order to solve the problems of single camouflage effectiveness evaluation method and insufficient quantitative analysis method, the cosine similarity principle was introduced to carry out simulation evaluation, and the theoretical analysis of visible light camouflage effectiveness evaluation was optimized. Based on the characteristics of color optical data, color histogram was used to show the color frequency distribution of target and background, and the difference of color fusion between sample target and background was studied. The luminance spatial characteristics were shown by luminance spatial distribution map, the luminance difference between the sample target and the background was explored. By collecting and calculating the pixel data of the target and the background image, the fusion effect of the target and the background was quantified. Based on the typical verification example, the correctness of the evaluation method was verified through the positive and negative comparative analysis. The results show that the cosine of the included angle between the image feature vector of the target and the background is 0.9982, and the fusion effect of the cosine similarity between the target and the background is respectively 0.9821 and 0.7324 by positive and negative comparison. Qualitative analysis and quantitative calculation show that cosine similarity theory can provide relevant algorithm support for camouflage effectiveness judgment and has certain practical value and application value.
In order to solve the problems of single camouflage effectiveness evaluation method and insufficient quantitative analysis method, the cosine similarity principle was introduced to carry out simulation evaluation, and the theoretical analysis of visible light camouflage effectiveness evaluation was optimized. Based on the characteristics of color optical data, color histogram was used to show the color frequency distribution of target and background, and the difference of color fusion between sample target and background was studied. The luminance spatial characteristics were shown by luminance spatial distribution map, the luminance difference between the sample target and the background was explored. By collecting and calculating the pixel data of the target and the background image, the fusion effect of the target and the background was quantified. Based on the typical verification example, the correctness of the evaluation method was verified through the positive and negative comparative analysis. The results show that the cosine of the included angle between the image feature vector of the target and the background is 0.9982, and the fusion effect of the cosine similarity between the target and the background is respectively 0.9821 and 0.7324 by positive and negative comparison. Qualitative analysis and quantitative calculation show that cosine similarity theory can provide relevant algorithm support for camouflage effectiveness judgment and has certain practical value and application value.
2022, 46(2): 267-273.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.019
Abstract:
In order to solve the problem of welding defects in Invar alloy welding, the technological parameters of Invar alloy lap welding (the thickness of the upper and lower plates with 1.5mm) for liquefied natural gas (LNG) ship sheet were studied. Though designing and manufacturing a gas protection box, by means of numerical simulation analysis and orthogonal experiment, the optimal process parameters of Invar alloy lap welding were obtained.The experimental results show that the porosity defects are effectively suppressed under complete shielding gas, and the optimal technological parameters for the lap welding of Invar alloy are obtained as: Laser power is 3.4kW, welding speed is 1.3m/min, defocus is +20mm, laser incident angle is 5°, and laser spot energy distribution is 2∶1, respectively. Under the optimal process parameters, the weld surface is silvery white, and there is no defect such as air holes. The hardness of the weld is smaller than that of the base metal but larger than that of the heat affected zone. The tensile strength is 417.16MPa, which is 94.8% of that of the base metal. The error between the simulation results and the test results is small, which proves the reliability of the simulation model established in this paper. This result is helpful for the construction of the later process parameter database of Invar laser lap welding.
In order to solve the problem of welding defects in Invar alloy welding, the technological parameters of Invar alloy lap welding (the thickness of the upper and lower plates with 1.5mm) for liquefied natural gas (LNG) ship sheet were studied. Though designing and manufacturing a gas protection box, by means of numerical simulation analysis and orthogonal experiment, the optimal process parameters of Invar alloy lap welding were obtained.The experimental results show that the porosity defects are effectively suppressed under complete shielding gas, and the optimal technological parameters for the lap welding of Invar alloy are obtained as: Laser power is 3.4kW, welding speed is 1.3m/min, defocus is +20mm, laser incident angle is 5°, and laser spot energy distribution is 2∶1, respectively. Under the optimal process parameters, the weld surface is silvery white, and there is no defect such as air holes. The hardness of the weld is smaller than that of the base metal but larger than that of the heat affected zone. The tensile strength is 417.16MPa, which is 94.8% of that of the base metal. The error between the simulation results and the test results is small, which proves the reliability of the simulation model established in this paper. This result is helpful for the construction of the later process parameter database of Invar laser lap welding.
2022, 46(2): 274-282.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.020
Abstract:
In order to improve the performance of the maximum 2-D segmentation, an image segmentation method based on improved sparrow algorithm (ITSSA) was proposed, which can decrease the amount of computation and shorten the time. Firstly, the reverse learning strategy and adaptive t-distribution variation were combined, while elite particles were introduced to expand the search range of the algorithm and to increase the local search ability of the algorithm in the later stage. Secondly, the firefly mechanism was used to perturb and mutate the optimal solution for the further increasement of the population diversity. Finally, the improved sparrow algorithm was used to find the maximum 2-D entropy of the image, and then the optimal threshold segmentation image was obtained. The results show that, the average running time of the proposed algorithm in the four images is 0.3695s, which is much lower than 1.7547s of the basic two-dimensional entropy algorithm and 5.7936s of the basic two-dimensional Otsu algorithm. The global search and local optimization ability of ITSSA, compared with the original sparrow algorithm, improves a lot, and the proposed segmentation method in this paper greatly shortens the traditional maximum 2-D entropy image segmentation method of running time. Apart from that, both the peak signal to noise ratio and the feature similarity index of this method increase, which has a certain application value.
In order to improve the performance of the maximum 2-D segmentation, an image segmentation method based on improved sparrow algorithm (ITSSA) was proposed, which can decrease the amount of computation and shorten the time. Firstly, the reverse learning strategy and adaptive t-distribution variation were combined, while elite particles were introduced to expand the search range of the algorithm and to increase the local search ability of the algorithm in the later stage. Secondly, the firefly mechanism was used to perturb and mutate the optimal solution for the further increasement of the population diversity. Finally, the improved sparrow algorithm was used to find the maximum 2-D entropy of the image, and then the optimal threshold segmentation image was obtained. The results show that, the average running time of the proposed algorithm in the four images is 0.3695s, which is much lower than 1.7547s of the basic two-dimensional entropy algorithm and 5.7936s of the basic two-dimensional Otsu algorithm. The global search and local optimization ability of ITSSA, compared with the original sparrow algorithm, improves a lot, and the proposed segmentation method in this paper greatly shortens the traditional maximum 2-D entropy image segmentation method of running time. Apart from that, both the peak signal to noise ratio and the feature similarity index of this method increase, which has a certain application value.
2022, 46(2): 283-287.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.021
Abstract:
To meet the demand of reconnaissance in modern military equipment, a novel conformal infrared optical system was presented. Two axial translation phase plate were used to correct the dynamic aberrations which were caused by the conformal structure.For the designed optical system, the working band was 3.7μm~4.8μm, the focal length was 40mm, the ratio of length to aperture was 1.0, the instantaneous angle was 2°, and the scan angle is ±15°, respectively. The results show that the modulation transfer function of each scan fields of view is greater than 0.6 with the nyquist frequency of 17lp/mm, and the optical transfer function is comparable to the diffraction limit. The spot of several scan fields is less than 30μm and falls within the area of one pixel. The designed optical system with well optical performance can be a suitable candidate for the application of the mid-infrared refrigerated focal plane array detector with the pixel size of 30μm×30μm. This research is potentially helpful for the further development and application of new imaging optical equipment in the military field.
To meet the demand of reconnaissance in modern military equipment, a novel conformal infrared optical system was presented. Two axial translation phase plate were used to correct the dynamic aberrations which were caused by the conformal structure.For the designed optical system, the working band was 3.7μm~4.8μm, the focal length was 40mm, the ratio of length to aperture was 1.0, the instantaneous angle was 2°, and the scan angle is ±15°, respectively. The results show that the modulation transfer function of each scan fields of view is greater than 0.6 with the nyquist frequency of 17lp/mm, and the optical transfer function is comparable to the diffraction limit. The spot of several scan fields is less than 30μm and falls within the area of one pixel. The designed optical system with well optical performance can be a suitable candidate for the application of the mid-infrared refrigerated focal plane array detector with the pixel size of 30μm×30μm. This research is potentially helpful for the further development and application of new imaging optical equipment in the military field.
2022, 46(2): 288-292.
doi: 10.7510/jgjs.issn.1001-3806.2022.02.022
Abstract:
In order to analyze the optical constants of the TiO2 thin film prepared by the sol-gel method, multi-layer TiO2 thin films were prepared by spin-coating, and the surface morphology was analyzed by scanning electron microscopy. The refractive index dispersion and porosity of the film were analyzed by ellipsometry. The fitting analysis was carried out, and the fitting results were verified by in-situ common-angle reflectance spectroscopy. The TiO2 thin film thickness, porosity, and refractive index dispersion curves were then obtained. The results show that the thickness of the TiO2 thin film has a linear relationship with the number of spin coatings. The porosity of the film is about 15% and has nothing to do with the number of spin coatings. The New Amorphous dispersion model can fit the ellipsometric spectrum of TiO2 thin film prepared by the sol-gel spin coating method in the 1.55eV~4.00eV band. This study provides a reference for the measurement of the optical constants of the TiO2 thin film prepared by the sol-gel method.
In order to analyze the optical constants of the TiO2 thin film prepared by the sol-gel method, multi-layer TiO2 thin films were prepared by spin-coating, and the surface morphology was analyzed by scanning electron microscopy. The refractive index dispersion and porosity of the film were analyzed by ellipsometry. The fitting analysis was carried out, and the fitting results were verified by in-situ common-angle reflectance spectroscopy. The TiO2 thin film thickness, porosity, and refractive index dispersion curves were then obtained. The results show that the thickness of the TiO2 thin film has a linear relationship with the number of spin coatings. The porosity of the film is about 15% and has nothing to do with the number of spin coatings. The New Amorphous dispersion model can fit the ellipsometric spectrum of TiO2 thin film prepared by the sol-gel spin coating method in the 1.55eV~4.00eV band. This study provides a reference for the measurement of the optical constants of the TiO2 thin film prepared by the sol-gel method.
