Optoelectronic measurement
2019, 48(11): 1113001.
doi: 10.3788/IRLA201948.1113001
As an important direction for the future development of star sensors, all-time star sensor technology can extend the application of star sensors to near space platforms such as stratospheric airships and high-altitude balloons. Due to the intense atmospheric background radiation during daytime, the detection capability of star sensors in visible band was significantly limited. The intensity of atmospheric background radiation in the short-wave infrared (SWIR) band was rapidly reduced compared to that in the visible detection band. Therefore, the application of SWIR imaging systems for star detection in the range of 0.9-1.7 m has become an effective solution for studying the all-time star sensor technology. In order to analyze and verify the feasibility of SWIR all-time star sensor, the all-time star sensor detection model was analyzed and the impact of SWIR detector noise on the detection capability was discussed in this paper. Then, the optical parameters of the all-time star sensor at a height of 20 km were determined through simulation calculation. The prototype of the all-time star sensor was developed based on SWIR detector. Combined with the star observation experiments at the ground, the detection performance of the prototype was tested and the correctness of the all-time sensor detection model was verified.
2019, 48(11): 1113002.
doi: 10.3788/IRLA201948.1113002
Time-of-flight measurement is one of the principles of 3D sensation systems. In recent years, with the development of semiconductor technology, time-of-flight measurement systems based on the signal correlation method have developed rapidly in the field of three-dimensional imaging due to its advantages of all solid-state components, high integration and low power consumption. The mathematical principles of correlation time-of-flight measurement techniques were systematically studied, its error sources were analysed, the mathematical models were constructed, and different types of measurement errors were compared. The research results show that light source error, multipath and ambient light interference are the main factors that restrict the measurement accuracy and application range of time-of-flight imaging systems.
2019, 48(11): 1113003.
doi: 10.3788/IRLA201948.1113003
In order to distinguish the scattered light generated by the three defects of micro-particles, sub-surface and micro-roughness existing above the super smooth surface, and to obtain the best region for detecting these three scattering mechanisms, combined the Bidirectional Reflectance Distribution Function (BRDF) with Jones matrix and the polarization coefficients of the three defects were given in the four polarization states ss, sp, ps, pp. On this basis, the relationship between the three defects and scattering azimuth in four polarization states was simulated and analyzed. The results show that these defects could be distinguished by using p-polarized scattering light induced by p-polarized incident light. According to the different relations between the three defects and the variation of scattering azimuth, the best area to distinguish three kinds of defects and its realization methods were given.
2019, 48(11): 1113004.
doi: 10.3788/IRLA201948.1113004
Classification of sea and land returns in airborne lidar was essential for the research of coastal zones and their changing nature. A method for classification using deep learning on the original airborne lidar echo was proposed. A fully connected neural network, and a one-dimensional convolutional neural network (CNN), were used on a training dataset and test datasets from in-situ measurements, and a classification accuracy of 99.6% was obtained. The model was utilized on the datasets from different areas, a classification accuracy of 95.6% was achieved and the processing speed was increased by about 52% compared to support vector machine (SVM) method. The results denote that the deep learning method is very effective for classification of airborne lidar echo waveforms with high precision and speed. It may present further use as a candidate method for classifying species on the sea floor with airborne laser bathymetry.
2019, 48(11): 1113005.
doi: 10.3788/IRLA201948.1113005
Aiming at the problem that the attitude measurement accuracy of Fine Guidance Sensor (FGS) was affected by the error of star point extraction system, a high-precision star point positioning system error compensation method based on Gradient Boosting Decision Tree (GBDT) fitting method was proposed. In order to solve the problems of less fitting samples and large differences in input characteristics, a decision tree that was insensitive to the input range and easy to train was used as the base model. Combining the boosting method in ensemble learning to generate a new base model to obtain the functional relationship between the systematic error and the detector fill rate, sampling window size, Gaussian width of star image and star point centroid coordinate calculation value, and based on this function relationship to the star point centroid. The coordinate estimate was systematically corrected. The experimental results show that compared with the support vector regression machine, the error of the high-precision star point localization algorithm based on GBDT is reduced by 60.6%. The corrected centroid error is 0.014 5 pixel, and the error is reduced by 61.5%.
2016, 45(8): 817001.
doi: 10.3788/IRLA201645.0817001
Large photo-electricity telescope plays a more and more important role in exploring objects in the space and astronomy observation, its detectivity and pointing precision are the main factors that affecting its development. Firstly, detailed analysis on different errors affecting the pointing precision of the telescope was conducted in the paper; then topology of the telescope was constructed and the spatial error pointing model was established based on multi-system theory; finally the relation between three axis differences and angle measurement errors was researched. Compared with traditional spherical function, a comprehensive item of errors were contained in the model which provided reference for error distribution and error correction.
2016, 45(8): 817003.
doi: 10.3788/IRLA201645.0817003
The technology of the measurement of relative position and pose between two spacecrafts based on laser lidar is one of the key technologies in many space applications, such as on-orbit servicing to satellites of losing control, debris removal, etc. Firstly, the current research at home and abroad was described. Secondly, the measurement technology principle of relative position and pose was introduced and the point cloud registration method was highlighted. Finally, the simulation experiment of the spacecraft simulator was given. The result shows that measurement of relative position and pose between two spacecrafts based on laser lidar method is reasonable and feasible and it has high accuracy. It meets the relative navigation mission requirements and provides a greater reference for the implementation of engineering applications.
2015, 44(S1): 104-108.
In the Gobi region of Xinjiang, the system of atmospheric coherent lengh measurement and micro-thermal meter were set up in the surface of lake for measuring atmospheric turbulence. The refractive index structure parameter was used to compute the atmospheric coherence length, the distinctness was analyzed also. The result shows that the time-interval of weak atmospheric turbulence is not obvious at sunset and sunrise in the autumn. At sunset, the time-interval of weak atmospheric turbulence mainly distributes about 9:00; at sunrise, the time-interval of weak atmospheric turbulence mainly distributes about 21:00. In the daytime, The time-interval of strong atmospheric turbulence lasts six to eight hours, and mainly distributes from 12:00 to 20:00. The strength of atmospheric turbulence in the nighttime is obvious stronger in the daytime, it is stabler by in the land.
2015, 44(S1): 109-112.
A non-gain microchannel plate (MCP) gated X-ray framing camera was reported. It is made up of four basic components, the non-gain MCP imager, the pinhole array, the picosecond gating pulse generator, and the CCD camera system. The temporal resolution was measured by using a fiber bunch. While the gating pulse with width of 145 ps and amplitude of -1.5 kV plus -300 V bias were applied on the non-gain MCP, the measured temporal resolution of this camera was about 59 ps. Furthermore, the relationship between the temporal resolution and the MCP bias voltage was obtained. The variation of the temporal resolution with the intensity of the output signal was also provided. The experimental results show that the temporal resolution is improved while the MCP bias voltage is decreased. However, the intensity of the output signal is reduced while the MCP bias voltage is decreased.
2015, 44(S1): 73-79.
In order to enhance the weak and asymmetrical image of small laser spot and suppress the noise information, eliminate unstable laser spot effect on the calculation results, a new method was proposed in this paper. Firstly, a multi-dimensional image cube was constructed by many images captured in different time, the primary information was concentrated in the first dimensional image, the correlation of each dimensional image was removed. Secondly, the first dimensional image was divided into laser spot and background by Kmeans method, the classified image was processed by mathematical morphology, the edge of largest spot was searched as edge of small laser spot. Finally, the least square method of circle fitting was used to calculate small laser spot center. The experimental results show that the method can improve the accurate rate on checking the weak and asymmetrical laser spot, the binary laser spot area obtained by new method is 97.15% of ideal spot area, the error of small laser spot center and radius is less than 2 pixels, and realize the accuracy measure of small laser spot in the integrated diagnostic system.
2015, 44(S1): 80-85.
The cat-eye effect based active laser detection technique has a broad prospect in antimissile and air defense field, while the distortion effect on the incident and reflected waves caused by aerodynamic flow field around the planes and missiles is an important part of the echo wave characteristic analysis. Facing the complicated physical process of the laser waves in the cat-eye lenses and aerodynamic flow field both in the incidence and reflection propagation, a Zemax based aero-optical distortion calculation method was proposed. Firstly, based on finite element theory, the aero-optical flow field was divided into multiple layers according to the refractive index gradient. Secondly, curve surface fitting of the interfaces between the layers was done with standard, even asphere and Zernike polynomial surface, then a multilayer lens group model with different refractive index was established in Zemax, and the whole incidence and reflection Zemax model was accomplished with imaging optical system added in. Take a typical missile model as the example, the computational fluid dynamics and optical propagation distortion simulation in Zemax were performed, the feasibility of this method was validated after comparing with the analytical results of ray tracing.
2015, 44(S1): 86-92.
The maximum range of active and passive laser range-gated detection system consists of the most far detection range of the visible/infrared system and the laser system. The furthest distance function of visible/infrared detector and the laser imaging were established respectively. The influence of the detector sensitivity, the transmission power, the laser emission angle and the atmospheric visibility on the maximum range was simulated. Two sets of range-gated system of 532 nm YAG laser and 860 nm solid-state laser were established. Simulation analysis system farthest distance is 11.2 km and 5.5 km respectively. 15.7 km, 10.9 km and 13 km targets are imaged using YAG laser. 1.3 km, 5.1 km and 6 km targets are imaged using solid-state laser. The most remote of the system is verified by comparing the distance between the targets. The experimental results show that the furthest distance from the theoretical calculation is basically consistent with the actual distance. The furthest distance function can reflect the actual performance of the system. It can be used as the basic reference for the evaluation of the system and it is an important reference for the design of the system.
2015, 44(S1): 93-98.
Based on the coupled wave equation of Stimulated Brillouin Scattering (SBS), the models of Brillouin frequency shift, the pump wave, Stokes wave and the acoustic field in multimode fiber were built. Analysis and comparison of the Brillouin sepectrum frequency, peak gain, linewidth and SBS threshold between the multimode and single mode fiber were conducted. And then the influences of optical fiber length, attenuation coefficient and numerical aperture on the SBS threshold were discussed. The results show that, multiple modes of the Brillouin scattering superposition lead to spectrum broadening, linewidth increase, peak gain decrease and frequency shift reduce. The SBS threshold of the graded index multimode optical fiber is larger than 80 mW, which is far larger than the single mode fiber. When the core diameter is same, the graded index multimode fiber is more susceptible to take place the SBS effect, whose numerical aperture has more influences on SBS threshold than the step index multimode fiber. The reported measurement results validate the theoretical analysis. The studies in this paper laid a theoretical foundation for the distributed Brillouin scattering sensing system based on multimode fiber.
2015, 44(S1): 99-103.
A distributed measurement system used in shooting range was introduced. A low-cost high-speed imaging equipment setting was set on the shooting range end. Through high-speed fiber optic imaging device, real-time data was transmitted to the remote safety zone that receives high-speed real-time data for storage and processing. The low-cost close-range setting method by more camera was presented. Besides, the front-end high speed camera, central optical fiber transmission, the composition and performance indicators of back-end acquisition system were also presented. Finally, two experiments were conducted for testing the bit error rate of the whole system, and a method to improve the bit error rate was advanced. This system not only can be used in the shooting range measuring target, but also has practical significance in the transmission and storage of large volume of data over a long distance.
2015, 44(8): 2351-2357.
The robot position accuracy is measuring the robot pose error between the command distance and the actual distance. To improve the robot accuracy, it needs to compensate on robot kinematic parameters. Laser tracker was used to measure the robot distance error in this article. The mapping between the actual kinematic parameters and the robot distance error model was obtained. Some kinematic parameters in modified D-H kinematic model that Hayati proposed can not be identified, therefore, the condition number was introduced to identify the distance error matrix. Through computing the condition number, the unidentified kinematic parameters in distance error kinematic model was deleted. Ultimately, the robot kinematic model using the identified kinematic parameters was compensated. It improves the robot accuracy apparently.
2015, 44(8): 2358-2363.
In order to realize the three-dimensional measurement of the objects regardless of far or near and expand the measurement range, a laser triangulation system based on synchronized scanners with LIDAR was established. Its principle, design and device selection were investigated. First, according to the synchronous scanning mechanism, the LIDAR technology was fused based on traditional three-dimensional measurement and the computational formula of the 3-D points was deduced. The selections of laser device, lens, and dichroscope, scanning servo motor, LIDAR acceptor and camera were analyzed based on system design requirement. After that the mechanical structure was designed and the light path of optical system was simulated by Zemax to prove the feasibility of principle. Finally, the back of light of APD was tested and the actual object was scanned to acquire 3-D point clouds. The experimental results show that the system is feasible.
2015, 44(8): 2364-2374.
In order to determine the influence of each error source on position and orientation determination error for three-field position and orientation device, the error analysis model of system was established. Firstly, the principle of three-field position and orientation device using space analytic geometry method was proposed, and the various error sources which affected accuracy of position and orientation was pointed out. Secondly, the characteristic and the probability distribution of error source were summarized; and the impact of error sources on position and orientation information pair was assessed. Then, the position and orientation error analysis model was established by using the homogeneous coordinate transformation matrix and principle of navigation. Finally, the error simulation was analyzed by using Monte Carlo method. The simulation results show that mean of position fix error is 121.0 m, mean of orientation fix error is 7.4, and it is pointed out that dominant error source is horizontal measurement error, followed by data error of deviation of vertical. Field experiments show that the mean of position fix error is 182.12 m; mean of orientation fix error is 9.3, and it is demonstrated that horizontal measurement error has the main influence on the overall outcome.
2015, 44(8): 2375-2381.
The variation of dark current is the key factor influencing the accuracy of the signals of detectors in the short-wave infrared(SWIR) band. Firstly, based on the analysis of the working principle of infrared detector G5853-21, an experiment was designed aiming to find the relation between dark current, temperature and reverse bias of the detector. Also, an error model was given for the infrared polarimeter by considering the influences of dark currents. Error models for Stokes parameters and the degree of polarization have been built for the polarimeter. Allowing for the specific conditions in the space environment,an optimization was designed to reduce the impacts of dark currents and temperature requirement was also given for the infrared polarimeter. The results indicated that, with accurate control of the temperature, the error of the degree of polarization, involving the measurement uncertainity and other noises, could be below 0.42%(with =0.3).
2015, 44(8): 2382-2388.
To advance the precision of the robot motion is one significant research goal of robot flexible processing issues. In the process, deformation mechanism of heat caused by temperature variation is found as one of the important reasons for affect the positioning error. The temperature compensation method suitable for the industry field was presented and testified through this paper. Effect of robot self-heating and scene environmental temperature factors on axial motion and the ending actuator positioning accuracy were analyzed. The thermal distribution and deformation models were built using finite element theory. Thermal compensation strategy was presented to accomplish the experimental and theoretical analysis of significant correlation between robot kinematics parameters and thermal models above, especially self-heating effect. It was convenient and suitable for industrial field environment. Thermal compensation is experimentally proved to carry the ability to adjust the position error of ending actuator to less than 0.1 mm.
2015, 44(8): 2389-2394.
With the improvement of lithograph resolution, the depth of focus (DOF) of lithographic projection objective is decreasing. In order to take full advantages of the restricted DOF, focusing is commonly used to adjust the wafer onto the ideal focal plane. As the key point of focusing, research on focus detection becomes very popular. The present focus method is based on four-quadrant detector or array CCD to grab light signal, which carries the defocusing amount information of the wafer, and then process image on computer. This method is slow and cannot satisfy the real-time requirement for focusing. Therefore, a focus detection method, which wass based on line scan CCD for image grabbing and FPGA for image processing, was provided. This method can detect the defocusing amount in high-speed by utilizing the high-speed of line scan CCD and FPGA's parallelism, combining with sub-pixel boundary detection algorithm based on polynomial interpolation. In order to compensate the defocusing amount, FPGA directly control the motor to drive the wafer stage up and down, making the focusing system a real-time closed loop. Due to reducing the computer links, this design has high-speed, high-resolution, low power consumption and low-cost characters.
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