激光照射系统远距离动态指示精度的测量方法

Measuring Method for Long-Distance Dynamic Indication Accuracy of Laser Irradiation System

为了满足实际工程应用对激光照射系统动态指示精度的高精度测量需求,提出一种无参考距离的双透视校正激光远场动态指示精度测量方法。采用同轴异源的设计方法,用可见光和近红外相机分别对靶板和光斑进行成像,通过室内标定获得双成像系统的配准矩阵,在外场测试中根据靶板合作目标获得可见光图像透视校正矩阵,结合两个矩阵推导出双透视校正矩阵,实现激光动态指示精度的测量。室内标定和室外动态指示精度测量实验的结果表明:双成像系统的图像配准标准误差为0.94 mm,动态指示精度的平均误差为2.45 mm,标准差为9.90 mm,可见所提系统可用于激光照射系统指示性能的室外考评。

Objective The indication accuracy of the laser irradiation system is an important factor influencing the strike accuracy of laser-guided weapons.When the irradiation target of the laser irradiation system is a moving target,the collected images possess a large perspective distortion,which affects the calculation of the real indication accuracy.Only a single camera cannot solve this problem well.Compared with the single-camera vertical target imaging measurement method,the measurement method that uses visible light and near-infrared cameras to simultaneously capture the vertical target has more advantages.The visible light and near-infrared cameras are used to detect the moving target and collect the laser spot,respectively.This method has higher imaging quality than the method of simultaneous imaging of the single-camera target and the spot.Note that to achieve good registration accuracy for a long focal length telephoto optical system,these conditions,including large effective registration target surface,controlled position accuracy of the positioning hole,and cooperation of the registration target plate must be considered.Also,the imaging of the registered target is susceptible to interference from the external environment.Simultaneously,due to the continuous movement of the target,the images collected by the dual-camera imaging system at different times have different perspective distortions.Furthermore,the accuracy of the perspective distortion correction affects the final measurement result of the indication accuracy.Thus,our proposed dual-imaging system measurement method without reference distance but with dual-perspective correction is useful for the measurement of the far-field dynamic indication accuracy of the laser irradiation system.Methods Before calculating the dynamic indication accuracy,we solve the essential problem that the images of the dual cameras do not overlap due to the mechanical structure and difference of cameras,that is,the image registration of the dual-imaging system.The problem of large-angle perspective distortion at different moments caused by movement is to correct the perspective distortion of the imaging system.Here visible light and near-infrared dual cameras of the coaxial optical system are used for telephoto imaging.Also,we design and construct the collimator star point array reticle and registration model of the visible light and near-infrared imaging system,respectively,to complete the indoor registration of the dual-imaging system.For the outdoor experiment,a theoretical model of dualperspective correction without reference distance is established using the cooperative target on the moving target board to realize the perspective distortion correction of the visible light target board and near-infrared laser spot images,and extract the cross target and laser spot from the corrected image.Next,the center position is calculated to obtain the far-field dynamic indication accuracy of the laser irradiation system.Results and Discussions At 1 km imaging distance for the dual-imaging system and 10 experiments,the registration and corresponding pixel standard deviations are 0.94 mm and 0.08 pixel,respectively.In the outdoor dynamic measurement accuracy calibration experiment of the measurement system and combined with the geometric imaging formula,the horizontal and vertical image spacing of the cooperative target point without perspective distortion on the target board image 1 km away are 2.18 and 0.92 mm,respectively.Continuous 340 frames of images are used for dynamic measurement accuracy statistical calculation,as shown in Fig.7(e).Results show that the horizontal and vertical measurement errors of the measurement system are mainly floating,and the maximum measurement error value is less than 28.28 mm,corresponding to the image.The deviation is 2 pixel.The average measurement error and standard deviation of the continuous 340 frame image pairs are 2.45 and 9.90 mm,respectively.The system can be effectively used in the outdoor evaluation of the indicating performance of the laser irradiation system.We note that the process of evaluating the outdoor dynamic indication accuracy of the laser irradiation system is the same as that of the outdoor dynamic measurement accuracy calibration experiment of the measurement system.However,a slight difference is that the cooperative self-inspection lamp becomes the actual laser irradiation system spot,that is,the detection target of the near-infrared camera is replaced and becomes the laser spot.Fig.8(b)shows the near-infrared laser spot image corrected by the dual perspective projection,and its signal-to-noise ratio is good.Fig.8(e)shows the result of fusing images of the two cameras.Here,the laser spot is located at the lower left of the target board.Fig.8(f)shows the dynamic accuracy test results of 376 consecutive frames of images(note:the direction of the y pixel coordinate axis of the image is from top to bottom).The measurement result data show that the dynamic indication error of the laser irradiator is floating with an average indication error and standard deviation of 354.65 and 58.28 mm,respectively.Conclusions In this paper,we propose a laser far-field dynamic indication accuracy measurement method without reference distance using dual-perspective correction.First,we simplify the image registration process of the dualimaging system and improve the image registration accuracy of the dual-camera imaging system for the registration standard deviation of 0.08 pixel.The actual registration standard deviation for a corresponding imaging distance at 1 km is 0.94 mm.Furthermore,we calibrate the dynamic measurement accuracy of the measurement system using a cooperative self-test lamp on the target plate by dual-perspective correction theoretical model without reference distance.The average measurement error of the measurement system is 2.45 mm with a dynamic measurement standard deviation of 9.90 mm.Finally,we perform practical dynamic indication accuracy tests of laser irradiation systems,to further verify the effectiveness of the proposed measurement method.