气动光学效应对激光雷达测距精度的影响及修正
发布时间：2018-07-31 14:08
【摘要】：高速飞行器周围会产生复杂的气流场，导致气体密度变化，形成不均匀的光学折射率分布，进而影响光传输。激光雷达可以探测目标的多种信息，并且具有极高的测距精度以及分辨率，但气动光学效应会严重破坏激光雷达系统的性能。因而研究这种气流场对激光雷达系统参数的影响，进而找到修正方法具有重要的研究意义。 本文研究了气动光学领域以及激光雷达测距精度的发展现状。目前对于气动光学的研究主要集中在提高数值模拟精确度，建立飞行参数与光学畸变的联系方程以及自适应光学修正，关于气动光学效应对激光雷达系统测距精度的研究却鲜有发表。另外，一直以来关于气动光学的研究一直集中在光学窗口附近的气动光学效应，以带有气动光学效应的飞行器为目标的激光雷达系统研究却很少被提到。本文旨在从该改角度出发对激光雷达测距精度进行研究。 首先，将气动光学的统计理论与大气光学进行了对比，根据气体物态参数与飞行状态的联系方程以及飞行状态与光学性质的对应关系，将流场研究引入到了气动光学效应研究中，并推导了斯特尔比与光程差均方根的联系方程，，为计算激光雷达回波能量衰减提供了理论基础。 其次，从光学折射率随飞行参数变化的关系式出发，研究分析了激波层所导致的光束偏折大小，给出了偏折角随飞行参数以及飞行器外形的变化曲线，最大偏折角可以达到1.5mr ad。研究分析了曲面激波层所导致的额外焦距，给出了额外焦距与飞行参数以及飞行器外形的变化关系。综合考虑激波的光束偏折效应以及额外焦距效应，对激光雷达系统的回波能量进行了计算，结果表明激波的存在可以使得回波能量衰减70%，极大的影响激光雷达系统。 最后，推导了一定条件下的激光雷达回波脉冲响应函数以及其与目标外形的关系式，利用光程差的实验结果，分析了目标表面湍流层对脉冲测距激光雷达回波波形的影响。采用光线追迹方法，计算了气动流场引起的波面畸变及斯特尔比，进而分析了激光雷达回波受到湍流流场散射所导致的能量衰减。综合波形畸变与能量衰减，对气动流场对激光雷达测距精度的影响进行了分析。结果表明，在湍流层的影响下，长度为12cm的目标最大可以产生约为36mm的测距误差，达到了目标尺度的30%，说明湍流层的散射效应对激光雷达测距精度具有不容忽略的作用。并且，峰值探测回波时间判定法会带来最小的测距误差。
[Abstract]:The complex airflow field around the high-speed vehicle will lead to the change of the gas density and the formation of an uneven optical refractive index distribution which will affect the light transmission. Lidar can detect many kinds of information of the target and has high ranging accuracy and resolution. But the performance of the lidar system can be seriously damaged by the aero-optical effect. Therefore, it is of great significance to study the effect of this airflow field on the parameters of lidar system, and to find a correction method. In this paper, the field of aero optics and the development of laser radar ranging accuracy are studied. At present, the research on aero-optics mainly focuses on improving the accuracy of numerical simulation, establishing the relation equation between flight parameters and optical distortion, and adaptive optical correction. However, the research on the accuracy of laser radar system based on aero-optical effect is rarely reported. In addition, the research on aero-optics has been focused on the aerodynamic effect near the optical window, but the research on the lidar system with the aero-optical effect is seldom mentioned. The purpose of this paper is to study the ranging accuracy of lidar from this angle. Firstly, the statistical theory of aero-optics is compared with that of atmospheric optics. According to the relation equation between gas physical state parameters and flight state, and the corresponding relation between flight state and optical properties, the statistical theory of aero-optics is compared with that of atmospheric optics. The study of flow field is introduced into the study of aero-optical effects, and the relation equation between Stelby and the root mean square of optical path difference is derived, which provides a theoretical basis for calculating the energy attenuation of laser radar echo. Secondly, based on the relation between optical refractive index and flight parameters, the beam deflection caused by shock wave layer is studied and analyzed. The curve of deflection angle with flight parameters and the shape of aircraft is given. The maximum deflection angle can reach 1.5mr ad. The additional focal length caused by the curved shock wave layer is analyzed and the relationship between the extra focal length and flight parameters and the shape of the aircraft is given. Considering the beam deflection effect of shock wave and the extra focal length effect, the echo energy of laser radar system is calculated. The results show that the shock wave can attenuate the echo energy by 70%, which greatly affects the laser radar system. Finally, the response function of laser radar echo and the relation between the response function and the shape of the target are derived. The influence of the turbulent layer of the target surface on the echo waveform of the pulse ranging laser radar is analyzed by using the experimental results of optical path difference. The wave surface distortion and Str ratio caused by aerodynamic flow field are calculated by ray tracing method, and the energy attenuation caused by the scattering of laser radar echo by turbulent flow field is analyzed. Combined with waveform distortion and energy attenuation, the influence of aerodynamic flow field on laser radar ranging accuracy is analyzed. The results show that under the influence of turbulent layer, the maximum range error of the target with length of 12cm is about 36mm, which reaches 30 points of the target scale, which indicates that the scattering effect of the turbulent layer can not be ignored to the accuracy of lidar ranging. Moreover, the peak detection echo time determination method will bring the minimum ranging error.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN958.98
本文编号：2155828
[Abstract]:The complex airflow field around the high-speed vehicle will lead to the change of the gas density and the formation of an uneven optical refractive index distribution which will affect the light transmission. Lidar can detect many kinds of information of the target and has high ranging accuracy and resolution. But the performance of the lidar system can be seriously damaged by the aero-optical effect. Therefore, it is of great significance to study the effect of this airflow field on the parameters of lidar system, and to find a correction method. In this paper, the field of aero optics and the development of laser radar ranging accuracy are studied. At present, the research on aero-optics mainly focuses on improving the accuracy of numerical simulation, establishing the relation equation between flight parameters and optical distortion, and adaptive optical correction. However, the research on the accuracy of laser radar system based on aero-optical effect is rarely reported. In addition, the research on aero-optics has been focused on the aerodynamic effect near the optical window, but the research on the lidar system with the aero-optical effect is seldom mentioned. The purpose of this paper is to study the ranging accuracy of lidar from this angle. Firstly, the statistical theory of aero-optics is compared with that of atmospheric optics. According to the relation equation between gas physical state parameters and flight state, and the corresponding relation between flight state and optical properties, the statistical theory of aero-optics is compared with that of atmospheric optics. The study of flow field is introduced into the study of aero-optical effects, and the relation equation between Stelby and the root mean square of optical path difference is derived, which provides a theoretical basis for calculating the energy attenuation of laser radar echo. Secondly, based on the relation between optical refractive index and flight parameters, the beam deflection caused by shock wave layer is studied and analyzed. The curve of deflection angle with flight parameters and the shape of aircraft is given. The maximum deflection angle can reach 1.5mr ad. The additional focal length caused by the curved shock wave layer is analyzed and the relationship between the extra focal length and flight parameters and the shape of the aircraft is given. Considering the beam deflection effect of shock wave and the extra focal length effect, the echo energy of laser radar system is calculated. The results show that the shock wave can attenuate the echo energy by 70%, which greatly affects the laser radar system. Finally, the response function of laser radar echo and the relation between the response function and the shape of the target are derived. The influence of the turbulent layer of the target surface on the echo waveform of the pulse ranging laser radar is analyzed by using the experimental results of optical path difference. The wave surface distortion and Str ratio caused by aerodynamic flow field are calculated by ray tracing method, and the energy attenuation caused by the scattering of laser radar echo by turbulent flow field is analyzed. Combined with waveform distortion and energy attenuation, the influence of aerodynamic flow field on laser radar ranging accuracy is analyzed. The results show that under the influence of turbulent layer, the maximum range error of the target with length of 12cm is about 36mm, which reaches 30 points of the target scale, which indicates that the scattering effect of the turbulent layer can not be ignored to the accuracy of lidar ranging. Moreover, the peak detection echo time determination method will bring the minimum ranging error.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN958.98
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