星地激光链路高精度跟瞄偏差角度获取方法研究

发布时间：2018-07-17 21:29

【摘要】：在星地激光通信系统中，激光束宽非常窄且接收视场小，为了快速建立和稳定保持长距离星地激光通信链路，激光通信终端必须具有高精度光束瞄准能力和高精度稳定跟踪能力。获得高精度跟瞄偏差角是长距离星地激光通信系统能够快速建立和稳定保持星地激光通信链路的重要保证。研究高精度跟瞄偏差角获取方法是十分紧迫和必要的。大气信道是星地激光通信信道的组成部分，作为信息载体的激光光束穿过大气层时会受到大气湍流的影响。在星地激光通信系统中，大气的湍流效应将影响信标激光光束在跟瞄系统接收终端形成的光斑光强分布，产生光斑畸变，降低瞄准捕获跟踪精度，使系统探测精度下降，瞄准偏差增大，接收功率降低，误码率增加，严重时甚至使星地激光链路的建立和保持变得困难。寻找能够有效校正或降低大气湍流影响的激光光斑中心获取方法，对星地激光链路的建立和稳定保持具有重要意义。本文研究的问题是，如何利用接收激光终端CMOS获得的入射激光信标光束的光斑光强分布，抑制大气湍流对跟瞄偏差角探测精度造成的影响，寻找获得高精度跟瞄偏差角的方法。这是星地激光通信链路快速建立和稳定保持的关键问题之一。首先对国内外星地卫星激光通信技术的研究进展进行了概述，，介绍了跟瞄偏差角度基础理论和探测机理，对跟瞄偏差角度的获取方法进行了分析。在此基础上进一步开展了本文的研究工作。提出了利用接收激光终端CMOS获得的光强分布灰度数字图像，再生纵横单向凸图像的方法。在滤除畸变二值含噪光斑图像噪声过程中，利用亮点像素到全图几何中心的欧氏距离作为判断该像素是否为单点噪声的判别准则。沿水平方向和垂直方向将光斑重构为单连通凸图像。以此再生纵横单向凸图像的几何中心接近入射激光光束在接收激光终端CMOS上的理想光斑中心，获得了更高精度的跟瞄偏差角。给出了再生纵横单向凸图像形心方法计算公式的几何意义。研究了滤除畸变二值含噪光斑图像单点噪声的滤波阈值获取。结合不断变化的大气湍流对光斑的影响，将每一帧受到大气扰动的畸变光斑与单点噪声的滤波阈值联系起来，提出了二值图像单点噪声滤波阈值长记忆动态优化方法，综合滤波阈值的历史记忆逐帧优化当前滤波阈值。提出高精度跟瞄偏差角获取的迭代频谱相位分布再生方法。根据衍射光学理论迭代生成频谱相位分布，只利用远距离接收激光终端CMOS获得的光强分布，构成入射激光光束在CMOS处的光场分布，经过近似卷积处理得到相位校正后光斑的光强分布，并结合再生纵横单向凸图像形心方法，稳定获得高精度跟瞄偏差角。给出了迭代频谱相位校正后，跟瞄偏差角度的计算公式。对迭代频谱相位分布再生方法确定迭代初值选取进行了研究。将相位迭代初值的选取与光斑峰值相联系，使相位迭代初值随着大气湍流不断变化。研究了采用迭代初值选取策略后迭代频谱相位分布再生方法收敛速度变化，并与传统方法相对比。分析了对迭代频谱相位分布再生方法产生的误差，确定校正系数。根据大气信道下光传播理论，模拟激光光束经长距离传输后的光畸变场，建立数值仿真模型。利用两个光学终端在距离为11.2km的城市链路上进行了星地激光链路跟瞄偏差角度探测地面模拟实验。通过仿真及实验对不同大气闪烁指数下的静态光斑图像和沿一定轨迹移动的动态光斑图像进行研究。本文提出了再生纵横单向凸图像形心方法和迭代频谱相位分布再生方法，利用星地激光通信系统接收激光终端CMOS获得的入射激光光束光斑的光强分布，抑制大气湍流对星地激光通信激光光束的影响，计算获得高精度跟瞄偏差角，有利于提高星地激光通信捕获瞄准跟踪系统的性能，快速建立并稳定保持星地激光通信链路。这些研究工作对于星地激光通信系统的优化设计和提高系统的通信性能具有重要理论指导意义和实际应用价值。
[Abstract]:In the satellite ground laser communication system, the width of the laser beam is very narrow and the receiving field is small. In order to quickly establish and maintain a long distance satellite and ground laser communication link, the laser communication terminal must have high precision beam aiming ability and high precision stability tracking ability. It is very urgent and necessary for us to establish and maintain the satellite laser communication link quickly.
Atmospheric channel is part of the satellite ground laser communication channel. The laser beam, as the information carrier, will be affected by atmospheric turbulence when it passes through the atmosphere. In the satellite ground laser communication system, the turbulence effect of the atmosphere will affect the intensity distribution of the light spot formed by the beacon laser beam in the receiving terminal of the tracking system, produce the spot distortion and reduce the aim. The quasi capture tracking accuracy reduces the accuracy of the system detection, increases the aim deviation, reduces the receiving power, and increases the bit error rate, and even makes the establishment and maintenance of the satellite and ground laser links difficult. Holding is of great significance.
The problem is how to use the light intensity distribution of the incident laser beacon beam obtained by the receiving laser terminal CMOS, to suppress the influence of the atmospheric turbulence on the detection accuracy of the tracking deviation angle, and to find a method to obtain the high precision tracking deviation angle. This is the key problem for the rapid establishment and stability of the satellite ground laser communication link. 1.
First, the research progress of satellite and earth satellite laser communication technology at home and abroad is summarized. The basic theory and detection mechanism of tracking deviation angle are introduced, and the method of obtaining the angle of tracking deviation is analyzed. On this basis, the research work of this paper is further carried out.
In the process of filtering the noise of the distorted two valued spot image, the Euclidean distance from the bright pixel to the full image geometry center is used as a criterion to judge whether the pixel is a single point noise in the process of filtering the noise of the distorted two valued spot, and it is a criterion to determine whether the pixel is a single point noise. In the vertical direction, the light spot is reconstructed into a single connected convex image. The geometric center of the regenerated longitudinal and horizontal unidirectional convex image is close to the ideal spot center of the incident laser beam on the receiving laser terminal CMOS. The higher precision of the tracking deviation angle is obtained. The geometric meaning of the calculation formula of the regenerated longitudinal and horizontal unidirectional convex image centroid method is given. In addition to the filtering threshold of the single point noise in the distorted two valued spot image, combined with the influence of the changing atmospheric turbulence on the spot, the dynamic optimization method of the threshold length memory of the two value image single point noise filtering is proposed, and the comprehensive filtering threshold is proposed. The historical memory optimizes the current filter threshold by frame by frame.
An iterative spectrum phase distribution regeneration method obtained by high precision tracking deviation angle is proposed. The spectrum phase distribution is generated according to the diffractive optical theory. Only the light intensity distribution obtained by the long distance receiving laser terminal CMOS is used to form the light field distribution of the incident laser beam at CMOS, and the phase corrected spot is obtained after the approximate convolution processing. The distribution of light intensity is combined with the regenerated vertical and horizontal convex image centroid method, and the high precision tracking deviation angle is obtained. The calculation formula of the angle of tracking deviation is given after the phase correction of iterative spectrum. The selection of iterative initial value is determined by the iterative method of phase distribution regeneration of the iterative spectrum. To make the phase iterative initial value change with the atmospheric turbulence, the convergence rate of the iterative spectrum phase distribution regeneration method after the iterative initial value selection strategy is studied and compared with the traditional method. The error generated by the iterative method of the phase distribution regeneration of the iterative spectrum is analyzed, and the correction coefficient is determined.
According to the theory of light propagation under the atmospheric channel, a numerical simulation model is established to simulate the optical distortion field of laser beam after long distance transmission. The ground simulation experiment of the satellite ground laser link heel tracking deviation angle is carried out on a city link with distance of 11.2km. Through simulation and experiment, two optical terminals are used in the different atmospheric scintillation index. The static spot image and the dynamic spot image moving along a certain trajectory are studied.
In this paper, the image centroid method of regenerated longitudinal and horizontal unidirectional convex image and the method of regenerating the phase distribution of the iterative spectrum are proposed. The intensity distribution of the incident laser beam obtained by the satellite ground laser communication system received by the laser terminal CMOS is used to suppress the influence of atmospheric turbulence on the laser beam of the satellite and ground laser communication, and the high precision tracking deviation angle is calculated. In order to improve the performance of the satellite ground laser communication acquisition and tracking system, the satellite ground laser communication link is quickly established and maintained. These research work has important theoretical guiding significance and practical application value for the optimization design of the satellite and ground laser communication system and the improvement of the communication performance of the system.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN929.1

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