2018 Vol. 39, No. 4
Display Method:
2018, 39(4): 447-452.
doi: 10.5768/JAO201839.0401001
Abstract:
Aiming at the photoelectric reconnaissance system working in the main operational direction, a method for obtaining the target data with low-cost photoelectric search equipment was proposed. The method of continuously scanning at a fixed angular velocity was utilized for the photodetector to capture the target at several times and to iterate and update the target azimuth and time data continuously, thus complete the calculation of the angular position and horizontal distance of the incoming target relative to the reconnaissance device.Furthermore, we deduced the mathematical model of target data.Through designing the simulation software, the experimental procedure can calculate the azimuth angle of target after the target enters into the observation boundary of reconnaissance equipment, and the information of target at different time azimuths, pitch angles and horizontal distances can be obtained.It can meet the tracking requirements for targets with a speed of no more than 500 m/s and a height of no more than 5 km in a state where the reconnaissance distance is not less than 20 km, realizes the simulation verification of the optical reconnaissance equipment, and provides reliable data for subsequent fire control calculations.
Aiming at the photoelectric reconnaissance system working in the main operational direction, a method for obtaining the target data with low-cost photoelectric search equipment was proposed. The method of continuously scanning at a fixed angular velocity was utilized for the photodetector to capture the target at several times and to iterate and update the target azimuth and time data continuously, thus complete the calculation of the angular position and horizontal distance of the incoming target relative to the reconnaissance device.Furthermore, we deduced the mathematical model of target data.Through designing the simulation software, the experimental procedure can calculate the azimuth angle of target after the target enters into the observation boundary of reconnaissance equipment, and the information of target at different time azimuths, pitch angles and horizontal distances can be obtained.It can meet the tracking requirements for targets with a speed of no more than 500 m/s and a height of no more than 5 km in a state where the reconnaissance distance is not less than 20 km, realizes the simulation verification of the optical reconnaissance equipment, and provides reliable data for subsequent fire control calculations.
2018, 39(4): 453-459.
doi: 10.5768/JAO201839.0401002
Abstract:
Starting from the light and miniaturization design angle of optoelectronic equipment, the optoelectronic equipment vibration system was taken as the research object. According to the shortcomings of the existing built-in rubber damping system, using metal damper, a suitable external metal damping system for airborne optoelectronic equipment was designed. Through the vibration and shock test of the vibration damping system, the natural frequency, the maximum transmission rate and the maximum impact displacement were measured. Finally, by comparing the stability accuracy of optoelectronic equipment in the two kinds of vibration system, it can be concluded that the external metal damping system and built-in rubber damping system can both make the stability accuracy of the optoelectronic equipment to meet the requirements for the use of less than 25 μrad. However, the external metal damping system can improve the internal effective space of the optoelectronic equipment, at the same time, the external metal damping system as a whole replaceable unit, it reduces the maintenance difficulty of the damping system, improves the overall maintainability of the optoelectronic equipment, which is possible for the integration of other optoelectronic sensors and the realization of light and miniaturization of airborne optoelectronic equipment.
Starting from the light and miniaturization design angle of optoelectronic equipment, the optoelectronic equipment vibration system was taken as the research object. According to the shortcomings of the existing built-in rubber damping system, using metal damper, a suitable external metal damping system for airborne optoelectronic equipment was designed. Through the vibration and shock test of the vibration damping system, the natural frequency, the maximum transmission rate and the maximum impact displacement were measured. Finally, by comparing the stability accuracy of optoelectronic equipment in the two kinds of vibration system, it can be concluded that the external metal damping system and built-in rubber damping system can both make the stability accuracy of the optoelectronic equipment to meet the requirements for the use of less than 25 μrad. However, the external metal damping system can improve the internal effective space of the optoelectronic equipment, at the same time, the external metal damping system as a whole replaceable unit, it reduces the maintenance difficulty of the damping system, improves the overall maintainability of the optoelectronic equipment, which is possible for the integration of other optoelectronic sensors and the realization of light and miniaturization of airborne optoelectronic equipment.
2018, 39(4): 460-465.
doi: 10.5768/JAO201839.0401003
Abstract:
In order to satisfy the omnidirectional laser detection, a structure of lidar based on 2D micro-electro-mechanical systems (MEMS) mirror scanning was proposed. The laser provides light signals to 6 scanning subsystems through a 1×6 high speed optical switch and it realizes 360° horizontal scanning by adding the field of view of 6 scanning subsystems together. The scanning range of each scanning subsystem can reach 60° × 30°, including a transmitting optical antenna that expands the MEMS mirror scanning angle and a large field of view(FOV) receiving optical antenna with gain. The transmitting optical antenna extends the scanning angle of the MEMS mirror from ±10° to ±30°, and the divergence is less than 0.2 mrad. The half image height of the laser echo in the receiving field angle passing through the receiving antenna on the detector is less than 1 mm and the gain of the receiving optical antenna is 3.65. By calculating the corrected lidar equation, the laser beam with a transmitting power of 20 W can achieve an echo power of ≥1 nW within a working distance of 100 m, and the result shows that the optical system can be applied to lidar system.
In order to satisfy the omnidirectional laser detection, a structure of lidar based on 2D micro-electro-mechanical systems (MEMS) mirror scanning was proposed. The laser provides light signals to 6 scanning subsystems through a 1×6 high speed optical switch and it realizes 360° horizontal scanning by adding the field of view of 6 scanning subsystems together. The scanning range of each scanning subsystem can reach 60° × 30°, including a transmitting optical antenna that expands the MEMS mirror scanning angle and a large field of view(FOV) receiving optical antenna with gain. The transmitting optical antenna extends the scanning angle of the MEMS mirror from ±10° to ±30°, and the divergence is less than 0.2 mrad. The half image height of the laser echo in the receiving field angle passing through the receiving antenna on the detector is less than 1 mm and the gain of the receiving optical antenna is 3.65. By calculating the corrected lidar equation, the laser beam with a transmitting power of 20 W can achieve an echo power of ≥1 nW within a working distance of 100 m, and the result shows that the optical system can be applied to lidar system.
2018, 39(4): 466-469.
doi: 10.5768/JAO201839.0401004
Abstract:
An ultra-high zoom optical system with the focal length of 8 mm~2 400 mm was designed for visible light band imaging. Using multi-component fully dynamic zoom structure, it does not increase the size of system on the premise of high variable ratio.Based on the ordinary diffractive lenses, the imaging characteristics and dispersion of harmonic diffractive element were analyzed, as well as the chromatic aberration and secondary spectrum introduced by reducing the long focal length. The new aspherical equations and characteristics were given, which could solve the problem of complex selection of the number of ordinary aspherical equations.On the basis of the above theory, the system was simulated by Zemax optical design software, and 4 harmonic diffraction surfaces and 4 new aspheric surfaces were introduced. The design results show that, at the Nyquist frequency of 50 lp/mm, the modulation transfer function curves are all above 0.5. The imaging quality is good, and it can be widely used in military and aerospace fields.
An ultra-high zoom optical system with the focal length of 8 mm~2 400 mm was designed for visible light band imaging. Using multi-component fully dynamic zoom structure, it does not increase the size of system on the premise of high variable ratio.Based on the ordinary diffractive lenses, the imaging characteristics and dispersion of harmonic diffractive element were analyzed, as well as the chromatic aberration and secondary spectrum introduced by reducing the long focal length. The new aspherical equations and characteristics were given, which could solve the problem of complex selection of the number of ordinary aspherical equations.On the basis of the above theory, the system was simulated by Zemax optical design software, and 4 harmonic diffraction surfaces and 4 new aspheric surfaces were introduced. The design results show that, at the Nyquist frequency of 50 lp/mm, the modulation transfer function curves are all above 0.5. The imaging quality is good, and it can be widely used in military and aerospace fields.
2018, 39(4): 470-475.
doi: 10.5768/JAO201839.0401005
Abstract:
To realize the function of flicker mitigation and dimming control in visible light communication system, a scheme of dimming control using joint coding modulation was proposed. In the scheme, the pulse width modulation (PWM) and the run length limited code (RLL) were adopted to match the duty cycle between the intra-frame and the inter-frame as well as to achieve the flicker mitigation respectively, and also the multi-pulse position modulation (MPPM) and the overlapped pulse position modulation (OPPM) were utilized to achieve light intensity adjustment for the purpose of improving the power efficiency or spectral efficiency. Theoretical analysis demonstrates that compared with a typical variable pulse position modulation (VPPM), the normalized power of the MPPM with a duty ratio of 0.9 can save 2.24 dB, and the spectrum utilization of the OPPM with a duty ratio of 0.5 is higher than 0.8 bps/Hz, which means OPPM has a higher spectrum efficiency. In addition, two modulation schemes based on the FPGA platform were implemented. The experimental results verify that the joint modulation dimming scheme can support the light source flicker mitigation and high-precision dimming control under the condition of ensuring the effective data transmission.
To realize the function of flicker mitigation and dimming control in visible light communication system, a scheme of dimming control using joint coding modulation was proposed. In the scheme, the pulse width modulation (PWM) and the run length limited code (RLL) were adopted to match the duty cycle between the intra-frame and the inter-frame as well as to achieve the flicker mitigation respectively, and also the multi-pulse position modulation (MPPM) and the overlapped pulse position modulation (OPPM) were utilized to achieve light intensity adjustment for the purpose of improving the power efficiency or spectral efficiency. Theoretical analysis demonstrates that compared with a typical variable pulse position modulation (VPPM), the normalized power of the MPPM with a duty ratio of 0.9 can save 2.24 dB, and the spectrum utilization of the OPPM with a duty ratio of 0.5 is higher than 0.8 bps/Hz, which means OPPM has a higher spectrum efficiency. In addition, two modulation schemes based on the FPGA platform were implemented. The experimental results verify that the joint modulation dimming scheme can support the light source flicker mitigation and high-precision dimming control under the condition of ensuring the effective data transmission.
2018, 39(4): 476-482.
doi: 10.5768/JAO201839.0401006
Abstract:
In order to solve the contradiction between the depth of field and the resolution of traditional microscope objective, the wavefront coding(WFC) 10× microscope objective was designed and researched based on WFC technique. Combining with traditional optical design software, an optimization method for cubic phase mask parameters based on modulation transfer function (MTF) consistency was used to achieve the point spread function(PSF) consistency of the system within a certain range near the image plane. In addition, a 10× microscope objective lens with an extended cubic phase mask was also designed to compare the effect of the depth-of-focus expansion using two different phase mask systems.Design results show that the cubic phase mask has a good focal depth expansion effect, which can extend the focal depth of the traditional 10× microscope objective by 15 times. Simulation and experimental results indicate that the encoded images of system are sharp within ±15 times depth of focus distance after filtering so as to extend the field depth of system.
In order to solve the contradiction between the depth of field and the resolution of traditional microscope objective, the wavefront coding(WFC) 10× microscope objective was designed and researched based on WFC technique. Combining with traditional optical design software, an optimization method for cubic phase mask parameters based on modulation transfer function (MTF) consistency was used to achieve the point spread function(PSF) consistency of the system within a certain range near the image plane. In addition, a 10× microscope objective lens with an extended cubic phase mask was also designed to compare the effect of the depth-of-focus expansion using two different phase mask systems.Design results show that the cubic phase mask has a good focal depth expansion effect, which can extend the focal depth of the traditional 10× microscope objective by 15 times. Simulation and experimental results indicate that the encoded images of system are sharp within ±15 times depth of focus distance after filtering so as to extend the field depth of system.
2018, 39(4): 483-490.
doi: 10.5768/JAO201839.0402001
Abstract:
The auto-focusing process applied to integrated camera is described as the lens looking for the maximum value of image definition evaluation function according to auto-focusing search algorithm. The auto-focusing search algorithm has a great influence on the focusing time and focusing accuracy of the whole auto-focusing process. In order to solve the problem that the existing algorithms fail to focus under light source scenes and no-detail scenes, a focus search algorithm based on scene prediction is proposed.The algorithm can intelligently analyze, judge and classify imaging scenes, and uses different search strategies in different scenarios to improve the stability and accuracy of auto-focus searching.At the same time, aiming at the problem that the existing algorithm is difficult to determine the direction of the peak of focus curve in defocus area, an fuzzy degree evaluation model is introduced, which can accurately determine the peak direction of the focus curve. Analysis of experimental data shows that the new algorithm has increased the focusing speed in the defocus area by 24.3%. Experiments verify that the new algorithm has high application value in the integrated camera imaging system based on Hass Hi3518A processor.
The auto-focusing process applied to integrated camera is described as the lens looking for the maximum value of image definition evaluation function according to auto-focusing search algorithm. The auto-focusing search algorithm has a great influence on the focusing time and focusing accuracy of the whole auto-focusing process. In order to solve the problem that the existing algorithms fail to focus under light source scenes and no-detail scenes, a focus search algorithm based on scene prediction is proposed.The algorithm can intelligently analyze, judge and classify imaging scenes, and uses different search strategies in different scenarios to improve the stability and accuracy of auto-focus searching.At the same time, aiming at the problem that the existing algorithm is difficult to determine the direction of the peak of focus curve in defocus area, an fuzzy degree evaluation model is introduced, which can accurately determine the peak direction of the focus curve. Analysis of experimental data shows that the new algorithm has increased the focusing speed in the defocus area by 24.3%. Experiments verify that the new algorithm has high application value in the integrated camera imaging system based on Hass Hi3518A processor.
2018, 39(4): 491-499.
doi: 10.5768/JAO201839.0402002
Abstract:
In order to improve the facial recognition rate under the change of posture and expression, combined with the ability of local plane distance (DLP) to judge the convexity of local curved surface, a face recognition method based on face equidistant invariant representation was proposed. Firstly, several operations such as distance constraint, location constraint and transformation were conducted on the depth image captured by the deep camera to get the clean and complete 3D face; then the nose tip was determined by the DLP value of every point on the 3D face, and the nasal root was determined by the clustering idea; secondly, the improved fast propulsion algorithm was used to calculate the geodesic distance matrix of face, then the threshold value was set and the effective face area was cut out; finally, the high-order moment feature of the effective face area was calculated as the feature vector of face for matching. The experimental results show that the recognition rate of this algorithm is close to 97% for different databases. Compared with the face recognition algorithms based on contour features and Gabor features, the recognition rate of this algorithm is increased by 14.1% and 8.3%, respectively, while having a high computing efficiency.
In order to improve the facial recognition rate under the change of posture and expression, combined with the ability of local plane distance (DLP) to judge the convexity of local curved surface, a face recognition method based on face equidistant invariant representation was proposed. Firstly, several operations such as distance constraint, location constraint and transformation were conducted on the depth image captured by the deep camera to get the clean and complete 3D face; then the nose tip was determined by the DLP value of every point on the 3D face, and the nasal root was determined by the clustering idea; secondly, the improved fast propulsion algorithm was used to calculate the geodesic distance matrix of face, then the threshold value was set and the effective face area was cut out; finally, the high-order moment feature of the effective face area was calculated as the feature vector of face for matching. The experimental results show that the recognition rate of this algorithm is close to 97% for different databases. Compared with the face recognition algorithms based on contour features and Gabor features, the recognition rate of this algorithm is increased by 14.1% and 8.3%, respectively, while having a high computing efficiency.
2018, 39(4): 500-504.
doi: 10.5768/JAO201839.0402003
Abstract:
In order to realize fast and precise centering with non-diffracting spot as straight-line datum under complex background noises, a centering method for non-diffracting images based on correlation-coefficient was proposed. In this algorithm, firstly the approximate position of the beam spot center is calculated based on the theory of light intensity gravity; then the image is converted to the grayscale image in polar coordinates, which generates the discrete-cycle sinusoidal signal with the same angular frequency as the spatial frequency of the spot image, and the phase angle is calculated and the average variance is evaluated for the phase information of each diameter; finally the correlation-coefficient is established in polar coordinate system for ideal beam center and actual beam center, which realizes centering the non-diffracting spot image. In the simulated noise environment, result shows that the proposed algorithm has strong ability of anti-noise interference, less time-consuming in comparison with other common algorithms, which realizes sub-pixel level accuracy.
In order to realize fast and precise centering with non-diffracting spot as straight-line datum under complex background noises, a centering method for non-diffracting images based on correlation-coefficient was proposed. In this algorithm, firstly the approximate position of the beam spot center is calculated based on the theory of light intensity gravity; then the image is converted to the grayscale image in polar coordinates, which generates the discrete-cycle sinusoidal signal with the same angular frequency as the spatial frequency of the spot image, and the phase angle is calculated and the average variance is evaluated for the phase information of each diameter; finally the correlation-coefficient is established in polar coordinate system for ideal beam center and actual beam center, which realizes centering the non-diffracting spot image. In the simulated noise environment, result shows that the proposed algorithm has strong ability of anti-noise interference, less time-consuming in comparison with other common algorithms, which realizes sub-pixel level accuracy.
2018, 39(4): 505-510.
doi: 10.5768/JAO201839.0402004
Abstract:
Maritime celestial navigation is an important autonomous navigation technology at sea, and the star identification is a key step in celestial navigation. Aiming at the problems of large data, redundant identification and low speed caused by the large field of view (FOV) of the fisheye camera celestial navigation system, a fisheye camera star identification method based on circular FOV segmentation was proposed. For the star image taken by a fisheye camera, the concentric circles were drawn around the center with different radii, and the FOV was divided into several equal-area circular areas. In the process of constructing the navigation feature database, the star argument was taken as the feature to construct a hash function, and the navigation feature database was stored into several sub-databases. In the identification process, a multi-triangulation identification algorithm based on the central star was used to proceed from the center to the edge of the circular FOV. The results of marine observation experiments show that the method can achieve an identification success rate of more than 90% with the time of 2.5 s on average, and it has good real-time performance.
Maritime celestial navigation is an important autonomous navigation technology at sea, and the star identification is a key step in celestial navigation. Aiming at the problems of large data, redundant identification and low speed caused by the large field of view (FOV) of the fisheye camera celestial navigation system, a fisheye camera star identification method based on circular FOV segmentation was proposed. For the star image taken by a fisheye camera, the concentric circles were drawn around the center with different radii, and the FOV was divided into several equal-area circular areas. In the process of constructing the navigation feature database, the star argument was taken as the feature to construct a hash function, and the navigation feature database was stored into several sub-databases. In the identification process, a multi-triangulation identification algorithm based on the central star was used to proceed from the center to the edge of the circular FOV. The results of marine observation experiments show that the method can achieve an identification success rate of more than 90% with the time of 2.5 s on average, and it has good real-time performance.
2018, 39(4): 511-517.
doi: 10.5768/JAO201839.0402005
Abstract:
In the foggy environment, the image quality is degraded due to scattering of light by atmospheric particles. For the image degradation under haze and other weather conditions, a global image polarization defogging method based on automatic parameter estimation was proposed.Using three polarization images of different angles, the degree of polarization of atmospheric light and atmospheric light at infinity was automatically estimated, and the image after defogging was obtained based on the atmospheric scattering model. The corresponding parameters were calculated from the three RGB color channels, making the algorithm suitable for the color field. Firstly, the dark channel method was used to estimate atmospheric light and transmission at infinity, and the transmission map was optimized by guided filtering. Then the global search method was used to estimate the degree of polarization of atmospheric light based on the non-correlation between atmospheric light and target light.Finally, clear target images were recovered from the atmospheric scattering model and enhanced using logarithmic transformation.This method can get clear defogging images under hazy weather, and in thick fog weather, the information entropy of defogged images is increased by about 21%, the average gradient is increased by about 2 times, and the standard deviation is increased by about 12%. Experimental results show that the proposed method can solve the problem of poor estimation parameters of artificial framing, improve the sharpness and contrast of the restored target image, and can be used for target detection and recognition of color images.
In the foggy environment, the image quality is degraded due to scattering of light by atmospheric particles. For the image degradation under haze and other weather conditions, a global image polarization defogging method based on automatic parameter estimation was proposed.Using three polarization images of different angles, the degree of polarization of atmospheric light and atmospheric light at infinity was automatically estimated, and the image after defogging was obtained based on the atmospheric scattering model. The corresponding parameters were calculated from the three RGB color channels, making the algorithm suitable for the color field. Firstly, the dark channel method was used to estimate atmospheric light and transmission at infinity, and the transmission map was optimized by guided filtering. Then the global search method was used to estimate the degree of polarization of atmospheric light based on the non-correlation between atmospheric light and target light.Finally, clear target images were recovered from the atmospheric scattering model and enhanced using logarithmic transformation.This method can get clear defogging images under hazy weather, and in thick fog weather, the information entropy of defogged images is increased by about 21%, the average gradient is increased by about 2 times, and the standard deviation is increased by about 12%. Experimental results show that the proposed method can solve the problem of poor estimation parameters of artificial framing, improve the sharpness and contrast of the restored target image, and can be used for target detection and recognition of color images.
2018, 39(4): 551-555.
Abstract:
In the foggy environment, the image quality is degraded due to scattering of light by atmospheric particles. For the image degradation under haze and other weather conditions, a global image polarization defogging method based on automatic parameter estimation was proposed.Using three polarization images of different angles, the degree of polarization of atmospheric light and atmospheric light at infinity was automatically estimated, and the image after defogging was obtained based on the atmospheric scattering model. The corresponding parameters were calculated from the three RGB color channels, making the algorithm suitable for the color field. Firstly, the dark channel method was used to estimate atmospheric light and transmission at infinity, and the transmission map was optimized by guided filtering. Then the global search method was used to estimate the degree of polarization of atmospheric light based on the non-correlation between atmospheric light and target light.Finally, clear target images were recovered from the atmospheric scattering model and enhanced using logarithmic transformation.This method can get clear defogging images under hazy weather, and in thick fog weather, the information entropy of defogged images is increased by about 21%, the average gradient is increased by about 2 times, and the standard deviation is increased by about 12%. Experimental results show that the proposed method can solve the problem of poor estimation parameters of artificial framing, improve the sharpness and contrast of the restored target image, and can be used for target detection and recognition of color images.
In the foggy environment, the image quality is degraded due to scattering of light by atmospheric particles. For the image degradation under haze and other weather conditions, a global image polarization defogging method based on automatic parameter estimation was proposed.Using three polarization images of different angles, the degree of polarization of atmospheric light and atmospheric light at infinity was automatically estimated, and the image after defogging was obtained based on the atmospheric scattering model. The corresponding parameters were calculated from the three RGB color channels, making the algorithm suitable for the color field. Firstly, the dark channel method was used to estimate atmospheric light and transmission at infinity, and the transmission map was optimized by guided filtering. Then the global search method was used to estimate the degree of polarization of atmospheric light based on the non-correlation between atmospheric light and target light.Finally, clear target images were recovered from the atmospheric scattering model and enhanced using logarithmic transformation.This method can get clear defogging images under hazy weather, and in thick fog weather, the information entropy of defogged images is increased by about 21%, the average gradient is increased by about 2 times, and the standard deviation is increased by about 12%. Experimental results show that the proposed method can solve the problem of poor estimation parameters of artificial framing, improve the sharpness and contrast of the restored target image, and can be used for target detection and recognition of color images.
2018, 39(4): 518-521.
doi: 10.5768/JAO201839.0403001
Abstract:
In order to solve the problem about the influence of non-uniform field-of-view(FOV) response of radiometer on the measurement results during the assessment of infrared target stealth effect, a method of calibration and measurement under the same solid angle was put forward. The influence of the FOV response non-uniformity on the measurement results caused by off-axis aberrations was eliminated by adopting the principle of the same optical path. The calibration and measurement of the IR target radiation intensity and other parameters was realized. Finally, we adopted standard blackbody as the measuring object, and the 3μm ~5μm integral radiation intensity was verified by using the proposed method. The result shows that the difference between the measured and standard values is less than 2%, and the measurement uncertainty is better than 3.7%(k=2).
In order to solve the problem about the influence of non-uniform field-of-view(FOV) response of radiometer on the measurement results during the assessment of infrared target stealth effect, a method of calibration and measurement under the same solid angle was put forward. The influence of the FOV response non-uniformity on the measurement results caused by off-axis aberrations was eliminated by adopting the principle of the same optical path. The calibration and measurement of the IR target radiation intensity and other parameters was realized. Finally, we adopted standard blackbody as the measuring object, and the 3μm ~5μm integral radiation intensity was verified by using the proposed method. The result shows that the difference between the measured and standard values is less than 2%, and the measurement uncertainty is better than 3.7%(k=2).
2018, 39(4): 522-527.
doi: 10.5768/JAO201839.0403002
Abstract:
In the existing three-dimensional measurement method for the surface topography of complex objects, in order to complete absolute phase measurement, it is usually necessary to process at least 6 fringe images, which limits the measurement speed. A method for obtaining three-dimensional shape of object by using two sinusoidal fringes and two triangle wave fringe patterns was proposed.The two-step phase-shifting sinusoidal fringe and two-step phase-shifting triangular wave fringe were calculated to obtain the wrapped phase, then the two-step phase-shifting triangular wave fringe was used to determine fringe order. Due to the decrease in number of projection images, the speed of measurement increased. In order to obtain the fringe order, the triangular wave fringe intensity modulation and intensity ratio were calculated. Compared with the calculation of the phase, the data processing time can be reduced, and the measurement speed can be further increased. At the same time, the influence on the surface reflectance can be reduced, and the measurement accuracy can be improved.For measuring the stepped standard block with maximum height of 39 mm, the maximum absolute error and the maximum root-mean-square (RMS) error are 0.045 mm and 0.041 mm, respectively. Experimental results demonstrate that the proposed method is effective and practical, the benefits are seen in the high-speed, real-time 3-D shape measurement of complex objects.
In the existing three-dimensional measurement method for the surface topography of complex objects, in order to complete absolute phase measurement, it is usually necessary to process at least 6 fringe images, which limits the measurement speed. A method for obtaining three-dimensional shape of object by using two sinusoidal fringes and two triangle wave fringe patterns was proposed.The two-step phase-shifting sinusoidal fringe and two-step phase-shifting triangular wave fringe were calculated to obtain the wrapped phase, then the two-step phase-shifting triangular wave fringe was used to determine fringe order. Due to the decrease in number of projection images, the speed of measurement increased. In order to obtain the fringe order, the triangular wave fringe intensity modulation and intensity ratio were calculated. Compared with the calculation of the phase, the data processing time can be reduced, and the measurement speed can be further increased. At the same time, the influence on the surface reflectance can be reduced, and the measurement accuracy can be improved.For measuring the stepped standard block with maximum height of 39 mm, the maximum absolute error and the maximum root-mean-square (RMS) error are 0.045 mm and 0.041 mm, respectively. Experimental results demonstrate that the proposed method is effective and practical, the benefits are seen in the high-speed, real-time 3-D shape measurement of complex objects.
2018, 39(4): 528-535.
doi: 10.5768/JAO201839.0403003
Abstract:
In the anti-pollution flashover work of the state grid system, it is impossible to measure the creepage distance of electrical equipment online currently. In view of this situation, we developed an on-line measurement system of creepage distance for high voltage insulator based on binocular stereo vision, proposed a method of using a conical off-axis mirror to produce the linear structured light. We discussed the feasibility of two ways to solve the interference problem of strong sunlight, one way used narrowband filters to enhance the contrast ratio of laser line in images, while the other way processed the images with adaptive threshold segmentation and feature point extraction by combining the maximum interclass variance method with the grayscale gravity method. After calibrating the system, the measurement accuracy for the creepage distance of high voltage insulators was tested. Experimental results show that the maximum relative error is 1.45% and the average relative error is 0.69%. It has been successfully applied to the on-line measurement of the creepage distance of various insulators in 110 kV substations.
In the anti-pollution flashover work of the state grid system, it is impossible to measure the creepage distance of electrical equipment online currently. In view of this situation, we developed an on-line measurement system of creepage distance for high voltage insulator based on binocular stereo vision, proposed a method of using a conical off-axis mirror to produce the linear structured light. We discussed the feasibility of two ways to solve the interference problem of strong sunlight, one way used narrowband filters to enhance the contrast ratio of laser line in images, while the other way processed the images with adaptive threshold segmentation and feature point extraction by combining the maximum interclass variance method with the grayscale gravity method. After calibrating the system, the measurement accuracy for the creepage distance of high voltage insulators was tested. Experimental results show that the maximum relative error is 1.45% and the average relative error is 0.69%. It has been successfully applied to the on-line measurement of the creepage distance of various insulators in 110 kV substations.
2018, 39(4): 536-544.
doi: 10.5768/JAO201839.0403004
Abstract:
Reflected radiation measurement(such as surface reflectance, surface radiance, etc.)from the radiometric calibration site is very important for the vicarious calibration of satellite sensors. Measurement error can be caused by the polarization effect of the reflected radiation from the radiometric calibration site, because of the fact that field instruments possess a certain degree of polarization sensitivity. A non-fixed-point measurement method based on multi-band polarization imager and tower crane and a fixed-point measurement method based on spectropolarimeter and bidirectional reflectance distribution function (BRDF) measurement frame were adopted to measure the multi-angular polarization distribution and local polarization homogeneity of the reflected radiation at the 490 nm and 670 nm bands in Dunhuang site. The results show that the reflected radiation from Dunhuang site possesses a certain degree of polarization characteristics. The polarization characteristics is wavelength-depended, the degree of polarization (DOP) of 490 nm band is obviously higher than 670 nm band, and the multi-angle polarization distribution is symmetric about the principle plane defined by the sun and instrument. In the principle plane, the DOP in forward scattering area (FSA) is higher than backward scattering area (BSA), and the DOP increased by the increasing of the view zenith angle (VZA). The angle distribution feature is fully consistent for the non-fixed-point method and fixed-point method. The local polarization homogeneity is about 6% for Φ100 m dimension area. The research on the polarization characteristics of reflected radiation from the calibration site is of great significance to the vicarious calibration scheme establishment and radiation measurement accuracy improvement.
Reflected radiation measurement(such as surface reflectance, surface radiance, etc.)from the radiometric calibration site is very important for the vicarious calibration of satellite sensors. Measurement error can be caused by the polarization effect of the reflected radiation from the radiometric calibration site, because of the fact that field instruments possess a certain degree of polarization sensitivity. A non-fixed-point measurement method based on multi-band polarization imager and tower crane and a fixed-point measurement method based on spectropolarimeter and bidirectional reflectance distribution function (BRDF) measurement frame were adopted to measure the multi-angular polarization distribution and local polarization homogeneity of the reflected radiation at the 490 nm and 670 nm bands in Dunhuang site. The results show that the reflected radiation from Dunhuang site possesses a certain degree of polarization characteristics. The polarization characteristics is wavelength-depended, the degree of polarization (DOP) of 490 nm band is obviously higher than 670 nm band, and the multi-angle polarization distribution is symmetric about the principle plane defined by the sun and instrument. In the principle plane, the DOP in forward scattering area (FSA) is higher than backward scattering area (BSA), and the DOP increased by the increasing of the view zenith angle (VZA). The angle distribution feature is fully consistent for the non-fixed-point method and fixed-point method. The local polarization homogeneity is about 6% for Φ100 m dimension area. The research on the polarization characteristics of reflected radiation from the calibration site is of great significance to the vicarious calibration scheme establishment and radiation measurement accuracy improvement.
2018, 39(4): 545-550.
doi: 10.5768/JAO201839.0403005
Abstract:
In order to satisfy the actual need of accurate measurement of SF6 gas concentration in the electrical system, a portable SF6 gas sensor was designed based on non-dispersive infrared (NDIR)differential detection principle, which adopted the single-beam and dual-wavelength optical structure. In order to improve the compactness and sensitivity of the system, the optical simulations of the straight and trapezoidal reflective gas chambers were carried out, and the gas chamber type was finally determined. As for designing hardware circuit, a small signal amplification filter circuit was designed to effectively extract the useful signal from the noise. The sensor uses the high precision and performance analog-to-digital converters to convert analog electrical signals into digital signals into single chip processor, which greatly improves the detection accuracy. The experimental results show the sensor can accurately measure the SF6 concentration in a range of 0~2×10-3, with the full range accuracy up to 4.2%.
In order to satisfy the actual need of accurate measurement of SF6 gas concentration in the electrical system, a portable SF6 gas sensor was designed based on non-dispersive infrared (NDIR)differential detection principle, which adopted the single-beam and dual-wavelength optical structure. In order to improve the compactness and sensitivity of the system, the optical simulations of the straight and trapezoidal reflective gas chambers were carried out, and the gas chamber type was finally determined. As for designing hardware circuit, a small signal amplification filter circuit was designed to effectively extract the useful signal from the noise. The sensor uses the high precision and performance analog-to-digital converters to convert analog electrical signals into digital signals into single chip processor, which greatly improves the detection accuracy. The experimental results show the sensor can accurately measure the SF6 concentration in a range of 0~2×10-3, with the full range accuracy up to 4.2%.
2018, 39(4): 556-562.
doi: 10.5768/JAO201839.0405001
Abstract:
In order to improve the packaging-structure efficiency of the surface mount package (SMP) light emitting diode (LED) packaging-structure, the simplified model of SMP LED packaging-structure was established as well as realized the continuous automatic generation, simulation and optimization of LED packaging-structure. The results show that under the same color temperature condition, there is a linear relationship between the luminous flux and the radiation flux, and the change of the side wall can cause the light flux first increased and then decreased. Beside, by testing three kinds of LEDs with different side wall angles, the trends of the luminous flux are identical both in the simulation results and the test results, and it is concluded that the optimal side wall angle is 60° for this type of packaging, which verify the correctness of the simulation.
In order to improve the packaging-structure efficiency of the surface mount package (SMP) light emitting diode (LED) packaging-structure, the simplified model of SMP LED packaging-structure was established as well as realized the continuous automatic generation, simulation and optimization of LED packaging-structure. The results show that under the same color temperature condition, there is a linear relationship between the luminous flux and the radiation flux, and the change of the side wall can cause the light flux first increased and then decreased. Beside, by testing three kinds of LEDs with different side wall angles, the trends of the luminous flux are identical both in the simulation results and the test results, and it is concluded that the optimal side wall angle is 60° for this type of packaging, which verify the correctness of the simulation.
2018, 39(4): 563-568.
doi: 10.5768/JAO201839.0405002
Abstract:
In order to realize high-precision assembly and adjustment of alt-az off-axis beam expanding optical system, the 4D interferometer was used to add plane lens matching the standard plane mirror to achieve self-collimation detection, and a dynamic detection method was proposed aiming at the problem of the tube needing for rotating around the pitch axis in actual. According to the actual assembly results, a space rectangular coordinate system was established, and the quadrature error of the two axes was calculated by using the maximum deviation of spot in rotation process. The results show, using this self-collimation detection and dynamic detection method, the surface figure accuracy root-mean-square(RMS) of primary mirror is 0.028 8λ@632.8 nm, the wave aberration RMS of the optical system is 0.131λ@632.8 nm, and the error of the two-axis orthogonality is 2.06″.
In order to realize high-precision assembly and adjustment of alt-az off-axis beam expanding optical system, the 4D interferometer was used to add plane lens matching the standard plane mirror to achieve self-collimation detection, and a dynamic detection method was proposed aiming at the problem of the tube needing for rotating around the pitch axis in actual. According to the actual assembly results, a space rectangular coordinate system was established, and the quadrature error of the two axes was calculated by using the maximum deviation of spot in rotation process. The results show, using this self-collimation detection and dynamic detection method, the surface figure accuracy root-mean-square(RMS) of primary mirror is 0.028 8λ@632.8 nm, the wave aberration RMS of the optical system is 0.131λ@632.8 nm, and the error of the two-axis orthogonality is 2.06″.
2018, 39(4): 569-573.
doi: 10.5768/JAO201839.0405003
Abstract:
An all-fiber tunable fiber laser with 2 μm band based on Fabry-Perot (F-P) fiber filter was designed and demonstrated experimentally. An amplified 1 550 nm semiconductor laser was adopted to pump a segment of Tm-Ho co-doped fiber (THDF), and then the optical gain at 2 μm band was obtained. The results indicate that the tuning range, linewidth and side-mode suppression ratio of the output laser are 195 nm, 0.05 nm and 66.98 dB, respectively. The whole structure adopts the THDF amplification structure, which can achieve output power of watt level.
An all-fiber tunable fiber laser with 2 μm band based on Fabry-Perot (F-P) fiber filter was designed and demonstrated experimentally. An amplified 1 550 nm semiconductor laser was adopted to pump a segment of Tm-Ho co-doped fiber (THDF), and then the optical gain at 2 μm band was obtained. The results indicate that the tuning range, linewidth and side-mode suppression ratio of the output laser are 195 nm, 0.05 nm and 66.98 dB, respectively. The whole structure adopts the THDF amplification structure, which can achieve output power of watt level.
2018, 39(4): 574-578.
doi: 10.5768/JAO201839.0406001
Abstract:
Through the analysis on the sensitivity of short-wave infrared(SWIR) detectors, the signal-to-noise ratio(SNR) of the target and the environmental detection output and the contrast, the detecting distances of SWIR thermal image to external scenes and laser spots under different atmospheric visibility and ambient illumination conditions were calculated and theoretically analyzed, moreover, the theoretical analysis was verified by testing.The results show that the detection distance of the laser spot by the SWIR thermal image is less than 3.5 km in the conditions of atmospheric visibility 1 km~3 km, ambient illumination 1 lx~1 000 lx, threshold SNR 2.25~10, and threshold contrast ratio 0.01~0.02.
Through the analysis on the sensitivity of short-wave infrared(SWIR) detectors, the signal-to-noise ratio(SNR) of the target and the environmental detection output and the contrast, the detecting distances of SWIR thermal image to external scenes and laser spots under different atmospheric visibility and ambient illumination conditions were calculated and theoretically analyzed, moreover, the theoretical analysis was verified by testing.The results show that the detection distance of the laser spot by the SWIR thermal image is less than 3.5 km in the conditions of atmospheric visibility 1 km~3 km, ambient illumination 1 lx~1 000 lx, threshold SNR 2.25~10, and threshold contrast ratio 0.01~0.02.
2018, 39(4): 579-584.
doi: 10.5768/JAO201839.0406002
Abstract:
According to the development needs of online infrared thermometry of metal organic chemical vapor deposition (MOCVD), integrating the character of Thomas Swan CCS MOCVD reaction chamber, and considering the particular conditions of the process of heating ratio control vacuum calcination, a simple 940 nm infrared thermometry apparatus was designed, which can measure the surface temperature of MOCVD graphite plate and the radial temperature profile at 19 probe points online. The infrared radiation intensity of the high-temperature graphite disk and the epitaxial wafer was detected by an infrared probe installed above the optical window, and the temperature was measured according to the Planck blackbody radiation formula and the spectral emissivity correction. The infrared temperature measuring device is mainly composed of a readable track, an infrared probe, a connecting plate, and a precision translation stage. The apparatus was used in the process of silicon(111) substrate growing epitaxial wafer with InGaN/GaN MQW vacuum calcination by MOCVD. Result shows that the lowest range of thermometry is equally 430℃; the accuracy is within 2.3℃ from 700 ℃ to 850℃, the accuracy is within 1℃ from 900 ℃ to 1100℃, the repeatability is within 0.6℃ from 700 ℃ to 1100℃. The apparatus work stably, without the need for reflectivity correction and effective hole area calibration.
According to the development needs of online infrared thermometry of metal organic chemical vapor deposition (MOCVD), integrating the character of Thomas Swan CCS MOCVD reaction chamber, and considering the particular conditions of the process of heating ratio control vacuum calcination, a simple 940 nm infrared thermometry apparatus was designed, which can measure the surface temperature of MOCVD graphite plate and the radial temperature profile at 19 probe points online. The infrared radiation intensity of the high-temperature graphite disk and the epitaxial wafer was detected by an infrared probe installed above the optical window, and the temperature was measured according to the Planck blackbody radiation formula and the spectral emissivity correction. The infrared temperature measuring device is mainly composed of a readable track, an infrared probe, a connecting plate, and a precision translation stage. The apparatus was used in the process of silicon(111) substrate growing epitaxial wafer with InGaN/GaN MQW vacuum calcination by MOCVD. Result shows that the lowest range of thermometry is equally 430℃; the accuracy is within 2.3℃ from 700 ℃ to 850℃, the accuracy is within 1℃ from 900 ℃ to 1100℃, the repeatability is within 0.6℃ from 700 ℃ to 1100℃. The apparatus work stably, without the need for reflectivity correction and effective hole area calibration.
2018, 39(4): 585-589.
doi: 10.5768/JAO201839.0408001
Abstract:
In order to achieve accurate temperature measurement in complex environments such as high corrosion, high radiation, and strong electromagnetic interference, a high-sensitivity all-fiber temperature sensor based on the sensing multi-wavelength Brillouin fiber laser (MBFL) and reference MBFL was designed and tested.The relation between the frequency shift of Brillouin scattering light and the temperature variation was analyzed theoretically and experimentally, the change in temperature was measured according to the frequency shift of the microwave signal obtained by outputting the Stokes laser signal pair beat frequency. The 10th-order Stokes pair was injected into a photodetector, which was selected by a tunable optical filter (TOF) with bandwidth of 0.1 nm.Furthermore, the accurate measurement of the temperature around the sensing MBFL could be realized. Results show that the temperature sensitivity is 10.829 MHz/℃ through beat frequency detection of 10th-order Stokes pair. And the measured temperature error is about 0.138 ℃ under the temperature variation of 40 ℃.
In order to achieve accurate temperature measurement in complex environments such as high corrosion, high radiation, and strong electromagnetic interference, a high-sensitivity all-fiber temperature sensor based on the sensing multi-wavelength Brillouin fiber laser (MBFL) and reference MBFL was designed and tested.The relation between the frequency shift of Brillouin scattering light and the temperature variation was analyzed theoretically and experimentally, the change in temperature was measured according to the frequency shift of the microwave signal obtained by outputting the Stokes laser signal pair beat frequency. The 10th-order Stokes pair was injected into a photodetector, which was selected by a tunable optical filter (TOF) with bandwidth of 0.1 nm.Furthermore, the accurate measurement of the temperature around the sensing MBFL could be realized. Results show that the temperature sensitivity is 10.829 MHz/℃ through beat frequency detection of 10th-order Stokes pair. And the measured temperature error is about 0.138 ℃ under the temperature variation of 40 ℃.
2018, 39(4): 590-594.
doi: 10.5768/JAO201839.0408002
Abstract:
Distributed optical fiber Raman temperature sensor (DTS) system is a set of measuring principle of Raman scattering light in optical fiber, based on the distributed temperature monitoring system, which uses Raman scattering light in optical fiber temperature and fiber strength state related principle for real-time monitoring of temperature. A set of 9 km optical fiber Raman temperature measurement system was designed, the Stokes and the anti-Stokes light was collected by data acquisition card, the temperature was accumulated and averaged at the computer terminal, and the weak signal was extracted from the system noise to increase its signal-to-noise ratio.With accumulative average of 16 000 times, the accuracy of temperature measurement can reach to ±2℃.
Distributed optical fiber Raman temperature sensor (DTS) system is a set of measuring principle of Raman scattering light in optical fiber, based on the distributed temperature monitoring system, which uses Raman scattering light in optical fiber temperature and fiber strength state related principle for real-time monitoring of temperature. A set of 9 km optical fiber Raman temperature measurement system was designed, the Stokes and the anti-Stokes light was collected by data acquisition card, the temperature was accumulated and averaged at the computer terminal, and the weak signal was extracted from the system noise to increase its signal-to-noise ratio.With accumulative average of 16 000 times, the accuracy of temperature measurement can reach to ±2℃.
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