Instrumentation, Measurement and Metrology|65 Article(s)
A Method for Evaluating Medium and High-earth Orbit Object Telescope's Precision by Beidou's Precise Ephemeris
Chang-ming LU, Xin GAO, Xi-yu LI, Mei-lin XIE, and Zhi-guo LI
In order to solve the lacking of calibration means when working in the field, the Beidou Navigation Satellite System(BDS) is used to evaluate telescopes' astronomy and axis orientation precision, which survey the Medium And High Earth Orbit Objects(MHEO). This research is dedicated to deduce the principle of astronomy and axis orientation, and testify the feasibility of evaluating the electro-optical telescope's accuracy with BDS by analysising the satellites' coverage, orbit pricision and brightness, which has big diameter. Firstly, we interpolate the regular BDS precise ephemeris by Lagrange polynomial, whose data interval is 5 minutes. With coordinate conversion, we get the apparent ascension and apparent declination in the agreement celestial coordinate system, azimuth and pitch in the station coordinate system, which are the true value for astronomy and axis orientation precision evaluation. A MHEO telescope's astronomy orientation precision is superior to 2″ and axis orientation precision is superior to 7″ by this method.
Acta Photonica Sinica
  • Publication Date: Oct. 15, 2020
  • Vol. 49 Issue 10 1012001 (2020)
Design of Compact Full-range Laser Methane Sensor with Wide Temperature Range
Tao PANG, Peng-shuai SUN, Zhi-rong ZHANG, Bian WU, Hua XIA, and Chi-min SHU
Account for big temperature difference and large dynamic range in the application environment, a compact full-range laser methane probe with a wide temperature range of -40~60℃ is designed. To reduce the volume of probe, cascade structure design is adopted for circuit. Single-chip microcomputer STM32F405 is used to realize laser temperature control, wavelength scanning modulation, digital phase-locked amplification and real-time inversion of concentration information. The circuit system and gas chamber are encapsulated in a stainless steel case of only Φ35 mm×60 mm, with windows in the middle to achieve physical isolation, ensuring intrinsic safety. At low concentration, wavelength modulation technology is used to ensure the measurement accuracy and measurement limit. Direct absorption spectroscopy technology is used to ensure the range and linearity, when the environmental concentration is high. At 25℃, standard atmospheric pressure, the measurement error of low concentration (-4, and the detection limit is 2.24×10-4. Under the condition of allowing baseline calibration or background subtraction, the limit could reach 6.026×10-5. The measurement error of high concentration (2~100%) is less than ±5% of the true value. At the ambient temperature of -40~60℃, 1.2% and 20% standard gases are used for the temperature performance test, respectively. The maximum relative measurement error are -3.3% and -3.15%, which fully met the requirement of national standards. It can be widely used in the urban comprehensive pipe corridor, gas station leakage monitoring, coal mine safety warning and other occasions.
Acta Photonica Sinica
  • Publication Date: Oct. 15, 2020
  • Vol. 49 Issue 10 1012002 (2020)
Research on CNN Denoising Algorithm Based on an Improved Mathematical Model for the Measurement of Far-field Focal Spot
Zheng-zhou WANG, Li WANG, Meng TAN, Ya-xuan DUAN, Wei WANG, Xin-feng TIAN, and Ji-tong WEI
Aim at the shortcomings that the mathematical model for the measurement of far-field focal spot with high dynamic range does not consider the influence of noise on the measurement results, this paper optimizes the measurement method of far-field focal spot based on schlieren from three aspects. Firstly, the mathematical model for the measurement of far-field focal spot based on schlieren is improved, and the noise is added to the mathematical model, which makes the mathematical model match with the real experimental environment, and improves the practicability and theoretical support of the mathematical model; Secondly, the denoising algorithm based on Convolution Neural Network (DnCNN) is used in the de-noise processing of the main lobe and side lobe CCD image, and the original denoising algorithm is improved effectively in this paper, which can remove the noise of different levels (0~75 dB) of the mainlobe and sidelobe 12-bit images; Finally, the whole experimental process of far-field focal spot measurement is simulated, including light splitting, attenuation, adding noise, schlieren sphere occlusion, denoising, attenuation magnification, focal spot reconstruction, etc., and the effective experimental results of reconstructed focal spot is obtained, which the correlation coefficient between the reconstructed and theoretical focal spot images is 0.998 9, and the error of dynamic range between the reconstructed and theoretical focal spot is 3.22%. The simulation results show that through the improvement of the mathematical model and the DnCNN denoising algorithm, the necessity of the improved mathematical model and the superior performance of the DnCNN denoising algorithm in improving the accuracy of the two-dimensional distribution and dynamic range of reconstructed focal spot are verified. The reliability of the measurement of far-field focal spot with high dynamic range based on schlieren is improved, and the accuracy and efficiency of the measurement of far-field focal spot in high dynamic range is met in the end.
Acta Photonica Sinica
  • Publication Date: Dec. 25, 2020
  • Vol. 49 Issue 12 118 (2020)
An Effectiveness Evaluation Method for Space-based Optical Imaging Systems
Xiao-tian LU, Feng LI, Bian XIAO, Xue YANG, Lei XIN, Ming LU, and Zhi-jia LIU
A novel effectiveness evaluation method was proposed based on the Johnson criteria and minimum resolvable contrast to evaluate effectiveness. In this process, target and background contrast, atmospheric transmission, detectors, and human eyes, are considered comprehensively. The noise equivalent contrast is introduced to measure the noise level of the detector, and the detection efficiency is measured by the joint probability of contrast and resolution, which can quantitatively and intuitively evaluate the detection ability of space-based optical imaging system. Verification experiments are carried out based on aerial and GF-2 satellite images. In aerial images, the recognition probability of car is 46%, the identification probability of aircraft is 73%, and the NIIRS level is 4.23; in GF-2 satellite images, the recognition probability of truck is 67%, the detection probability of small ship is 63%, and the NIIRS level is 4.53. The results show that the probability calculated by our method is basically consistent with the subjective judgment of human eyes, which is basically consistent with the NIIRS. The results prove the effectiveness of the method. Our method is of great significance to the design of space-based imaging systems and the evaluation of the on-orbit satellite detection capability.
Acta Photonica Sinica
  • Publication Date: Dec. 25, 2020
  • Vol. 49 Issue 12 138 (2020)
A Specular Stepped Surface Profile Measurement System Based on Fringe Reflection Principle with Micrometer-level Height Resolution
Xin-jun WAN, Song LÜ, Ke SONG, and Shu-ping XIE
A fringe reflection three dimensional (3D) profile measurement system is proposed for micrometer-level height stepped mirrors. A systematic theoretical analysis of fringe reflection ray path is conducted, showing that by proper selection of the structure parameters including the ray incident angle, the Liquid Crystal Display(LCD) screen orientation angle and the LCD screen pixel size, the fringe reflection system can resolve micron and even sub-micron level stepped mirrors. A micrometer-level resolution fringe reflection measurement setup for stepped mirrors is constructed, which calculates the fringe phase using the four-step phase shift method, determines the reflected light equation using the moving screen method and reconstructs the 3D shape based on triangulation method. A stepped mirror sample with 5 μm and 10 μm steps is finally measured. The measurement uncertainty is within 0.5 μm and the discrepancy with the commercial system result is less than 0.5 μm, which proves the feasibility of the designing method. The result of this paper can be of great reference to the 3D reconstruction study of specular surfaces with diffractive structures.
Acta Photonica Sinica
  • Publication Date: Apr. 01, 2020
  • Vol. 49 Issue 4 0412001 (2020)
Specular Normal Calibration Technology of Point Source
Rui-jin LI, Li-ming ZHANG, Xin LI, Wei WANG, Jia-wei LI, and Jun HAO
In the process of on-orbit radiation calibration, based on reflective point light sources, the modeling of specular normal calibration is inadequate. Aiming at this problem, a specular normal calibration and vector control algorithm based on reflector and camera geometry model is presented. The geometrical placement error between the camera and the reflector is solved by solving the model. The relationship between the centroid coordinates of the solar image and the normal direction of the reflector is established. The multi-point automatic calibration of the specular normal is realized. The method improves the pointing accuracy of the system and specular normal calibration accuracy. The experiment results show that the geometric model anti-solves the centroid coordinates at different times, which for multi-point specular normal calibration. The standard errors of the angular resolution of the sun pixels observed by the camera are 0.021 65° in the X-axis direction and 0.019 82° in the Y-axis direction. The error of the synthetic angle resolution is 0.029 36 °. The accuracy of calibration is better than that of the solar observer to the specular normal calibration. The method realizes the automatic calibration process of the camera observing the solar image instead of manually observing, and expands calibration flexibility. Comprehensive pointing accuracy of system is better than 0.1°. It lays the foundation for on-orbit radiation calibration and modulation transfer function detection of point light source array of networking automation of fixed experimental sites centrally control different energy levels gradients.
Acta Photonica Sinica
  • Publication Date: Apr. 01, 2020
  • Vol. 49 Issue 4 0412002 (2020)
Morphology Detection of Optical Components Based on Hysteresis Nonlinear Compensation System
Fang WANG, Qing-jie LU, Jin-cheng ZHUANG, Quan-zhao WANG, and Sen HAN
In order to reduce the error of phase calculation caused by the hysteresis nonlinear of piezoelectric ceramic actuator in phase-shifting interferometer, a control system for a piezoelectric ceramic actuator is designed. The high precision resistance strain sensor and signal conditioning circuit based on the principle of phase-locked amplification are used to detect the displacement of the piezoelectric ceramic actuator. A polynomial mathematical model is established to describe the hysteresis nonlinearity. And then, a feed-forward open-loop control method is proposed to compensate for the hysteresis nonlinearity. Finally, based on the proposed scheme, a tracking control experiment of the desired trajectory of the piezoelectric ceramic actuator is performed. At the same time, a compensation control system and an interferometer are used to detect the surface morphology of the optical element. The experimental results show that after compensation, the tracking error of the piezoelectric ceramic actuator is between -0.156 μm and +0.078 μm, and the hysteresis nonlinearity is reduced from 10.4% to 2.4%, and the surface shape undulated height Root Mean Square (RMS) and Peak Valley (PV) of the optical element measured by the interferometer are changed by 0.795 nm and 3.937 nm respectively. It shows that this system is of great significance for the high-precision shape detection of optical components.
Acta Photonica Sinica
  • Publication Date: Jun. 01, 2020
  • Vol. 49 Issue 6 0612001 (2020)
Simultaneous Measurement of Displacement and Slope with Dual-function Digital Speckle Pattern Interferometry
Yang-yang LI, Si-jin WU, Wei-xian LI, and Ming-li DONG
In order to meet the needs of multi-parameter variable evaluation of composite materials under complex loads in nondestructive testing, a dual-function digital speckle pattern interferometry system based on optical multiplexing is proposed to realize the measurement functions of both digital speckle pattern interferometry and digital shearography. By controlling one of the combinations of a mirror and quarter-wave plate, the optical setup of digital speckle pattern interferometry is formed when the combination is in the first position, allowing the out-of-plane displacement to be measured. The optical setup of digital shearography is formed to realize measurement of slope when the combination is in the second position. During the process of measurement, the out-of-plane displacement and slope of the object surface due to a single load can be simultaneously measured by simply switching the position of the combination. The optical setup of the dual-function digital speckle pattern interferometry enjoys the advantages of simple structure and high switching efficiency. High quality measurement results of displacement and slope can be obtained using the dual-function digital speckle pattern interferometry. It has been proved experimentally that the dual-function digital speckle pattern interferometry is suitable for field use in nondestructive testing of composite materials due to its superior performance in anti-interference and high-sensitivity testing.
Acta Photonica Sinica
  • Publication Date: Jun. 01, 2020
  • Vol. 49 Issue 6 0612002 (2020)
Realizations of Luminance Units in Range of 10~200 000 cd/m2
Liang Lü, and Xiao-mei JIANG
In order to satisfy the increasing calibration demand for high range luminance and improve the luminance calibration ability in China, a new generation of national luminance work standard was established which covers the range of 10~200 000 cd/m2. A twin light source injection adjustable high luminance uniform source was developed, and a precision limiting aperture was installed at the export of the source. The realization of the unitsc based on integrating sphere source method was introduced, and the key system characteristics were analyzed by experimental data, including the stability and spatial output characteristics of source, the position accuracy of adjustment, the linearity and the spectral mismatch error of the standard photometer etc. Finally the realized scale was transferred to a standard luminance meter which would be used as a transfer-reference. The relative expanded uncertainty of the new cd/m2 realization system is 0.7% (coverage factor is 2). Comparison between the proposed system and the current luminance work standard (3~1 500 cd/m2) shows a deviation less than 0.2%. The upper range of the proposed realization system is increased by 2 orders of magnitude compared with the original standard, and coveres the ranges of normal luminance meters, which can well satisfy the calibration demand in the high level luminance application of industry.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2020
  • Vol. 49 Issue 7 712001 (2020)
Deformation Measurement of Thin-walled Part Based on Binocular Vision
Li XING, Hong-zhi ZHANG, Xi CHEN, and Gang WANG
Aiming at the problem that the deformation measurement of thin-walled part is difficult and complicated, a method of deformation measurement of thin-walled part based on binocular vision is proposed. For the surface deformation of the part, a rigid metal block with reference coordinate system markers is installed on the measured part, and the designed coded targets and color circular markers are pasted on the surface of the part. The effective image region of the reference coordinate system and the coded targets are segmented by the color circular markers, which can eliminate the interferential image features. The identification and detection of coordinate system markers and coded targets are carried out, which realizes the accurate location of centers by using the designed corner structure, and then the 3D coordinates of the measurement points are calculated. The surface deformation of the part is calculated by comparing the changes of the 3D coordinates of the measurement points before and after part deformation. For the edge deformation of part, the improved Canny algorithm is used to extract the edge contour information of part, then the stereo matching and 3D reconstruction are carried out based on epipolar constraint and gray similarity. The experimental results show that the measurement method is reasonable and effective, and the measurement accuracy meets the requirements.
Acta Photonica Sinica
  • Publication Date: Aug. 25, 2020
  • Vol. 49 Issue 7 712002 (2020)