星载大气激光雷达光机集成分析的研究
文献类型：学位论文
| 作者 | 穆永吉 |
| 文献子类 | 博士 |
| 导师 | 陈卫标 |
| 关键词 | 激光雷达，光机集成分析，有限元分析，光学设计，Zernike拟合 Lidar, Integrated optomechanical analysis, Finite element analysis, Optical design, Zernike Fitting |
| 其他题名 | Research on Integrated Optomechanical Anlysis of Spaceborne Aerosol Lidar |
| 英文摘要 | 地球大气环境监测是地球科学的重要研究内容之一，激光雷达因其测量精度高、作用距离远且具有剖面测量能力，并且结合不同的发射波段可探测不同目标等优点，在大气环境监测中一直受到重视并不断发展。但由于激光主动探测原理的特性，限制了激光雷达的探测范围。为了能够在全球范围内对大气进行探测，星载大气激光雷达是最理想的解决方案。然而，空间特殊工作环境对大型激光雷达系统的设计要求非常严苛。在星载激光雷达的设计阶段需要进行大量的仿真分析来评估系统性能，从而对设计进行闭环迭代。在此背景下，本论文开展了星载大气激光雷达的光机集成分析的研究。 本论文介绍了目前国际上已发射升空的大气激光雷达及其参数性能，并且论述了热光机集成仿真分析的概念和必要性。有别于传统设计流程中，各学科领域内的技术指标流式传输的方式，光机集成分析能够以系统的光学性能指标对系统的结构设计、热设计作为评价指导，从而在星载激光雷达的光机系统设计过程中形成闭环。 星载大气激光雷达的工作波段为532nm、1572nm以及1064nm。其光学系统主要为发射光学、接收望远镜、光电探测单元以及视轴监视四个部分。激光雷达的接收望远镜为有效口径Φ1m的Ritchey-Chretien系统，有效接收视场全角为0.15mrad，镜体材料为SiC，并经轻量化处理。光电探测单元在接收望远镜焦平面处与接收望远镜耦合，回波信号经光电探测单元中的三波长准直透镜组准直后，分为三个不同波长的探测通道。视轴监测单元包含固定于星敏结构上的绝对参考光，并具有监测发射光轴与收发光轴对准偏差的能力。星载大气激光雷达的结构布局以光学基板为基准，接收望远镜及发射望远镜安装于光学基板前端；光电探测单元、发射光路与激光器、视轴监视单元安装于光学基板背侧。光学基板材料为铝基碳化硅复合材料，且为轻量化结构。结合星载大气激光雷达的光机结构与地球低轨空间辐射环境作为输入条件，本文对其进行光机集成分析，以得到系统的光学性能。 文中扼要介绍了结构分析中的有限元方法基本理论，并对空间光机学系统中常用的材料性能做了介绍。对于光机系统的集成分析来说，在机械结构设计及分析领域内，有限元仿真分析得到的结果为离散的节点形变数据；而在光学设计及分析领域内，模型是通过数学描述建立的，即光学表面通过相对位置关系以及面型参数进行定义。因此，光机集成分析的结果数据在学科间进行传输时便需要进行相关的处理。本文着重介绍了将有限元仿真分析得到的点云数据分离为光学表面的刚体位移以及弹性形变两部分的方法。通过齐次坐标转换对光学表面进行刚体位移计算，并将剩余的形变误差拟合为光学模型中通用的Zernike多项式，从而实现光机系统有限元分析的结果向光学模型中的传输。 本文为仿真结果数据跨学科整合设计了相应程序，从而避免了由于人工操作大量数据而造成的错误。并通过定量化的分析，研究了坐标变换的算法和Zernike拟合的算法精度。 在此基础上，本文论述了在光机集成分析过程中，光学元件的建模方法，主要为：单点模型，二维薄壳模型与三维实体模型；针对轻量化反射镜，可通过等效刚度模型进行建模的简化，三维薄壳模型则是轻量化反射镜较为精准的模型。最后，本文从重力卸载、接收望远镜主次镜温度梯度、次镜支撑筒温度梯度以及光学基板的温度梯度等几个方面分析了星载激光雷达收发光轴对准精度的偏差。并将以上分析结果用于星载激光雷达的热控设计。对重力卸载进行了垂直与平行接收望远镜光轴两种情况进行了分析，结果显示，在垂轴方向，发射光轴与接收光轴的对准偏差最大将达到152.67μrad；在平行方向，收发光轴对准偏差最大为58.12μrad。对系统关键元部件的分析显示，在接收主镜反射面内横向温度偏差为0.5℃时，收发光轴对准偏差较小，为0.2μrad；次镜支撑筒在垂轴方向温差2℃时的对准偏差为9.6μrad；光学基板作为关键部件，其在垂轴方向温差2℃时，引起的最大视轴对准偏差为16.44μrad，在径向温差2℃时，引起的最大偏差为37.32μrad。最后，结合系统的温控设计与在轨工况环境，对星载激光雷达进行了综合分析，在轨环境恶劣的工况下，收发视轴的对准偏差最大为98.33μrad，信噪比（SNR）将下降82.6%，为发射激光指向在轨调节方案的确定提供了重要设计数据。; The monitoring of earth's atmospheric environment is one of the important research areas of earth science. Lidar is attractive and is developed continuously in atmospheric environment monitoring due to its advantages of high measurement accuracy profiles measurement, long detection range, and ability to detect different targets in combination with different emission wavelength. In order to be able to detect the atmosphere globally, the spaceborne lidar is the ideal solution. However, the low-temperature and zero gravity environment in space are hard to design large-scale lidar equipment. In the design phase of the spaceborne lidar, a large amount of analysis work is needed to evaluate the performance of the system, and then the further design is closed-loop iterative. The integration thermo-optomechanical analysis of spaceborne lidar is studied in this dissertation. This dissertation introduces the launched lidar overseas and its system performance. The concept and necessity of the integrated thermal-optomechanical analysis is discussed. Being different from the traditional design process, which is that the technical targets in different disciplines are passed one by one, the integrated thermo-optomechanical analysis can rely on the system's optical performance. The thermal design of the lidar system then is led by the analysis result. Therefore, a closed loop analysis of the lidar optomechanical system design process is presented. The operational wavelengths of the spaceborne lidar are 532 nm, 1572 nm, and 1064 nm. Its optical system mainly includes four parts: transmitter optics, receiving telescope, photoelectric detection unit and boresight monitoring unit. The lidar receiving telescope is a Ritchey-Chretien system with an effective aperture of Φ 1 m. The effective receiving full field of view is 0.15 mrad. The mirror material is SiC, and is lightweighted. The photoelectric detection unit is coupled with the receiving telescope at the focal plane. After the signal light is collimated by the three-wavelength collimator in the photo detecting unit, it is divided into three detection channels with different wavelengths. The boresight monitoring unit contains absolute reference laser source fixed on the star sensitive structure and has the ability to monitor the deviation of the aiming axis of the receiver and transmitter. The structure of the spaceborne atmospheric lidar is based on an optical base. The receiving and transmitting telescopes are mounted on the front of the optical base. The photoelectric detection unit, the transmitter path and the laser, the boresight monitoring unit are mounted on the back side of the optical base. The optical base material is aluminum-based silicon carbide and has a lightweight structure. Combining the optical structure of the spaceborne lidar with the earth's low-orbit environment as input conditions, this dissertation conducts optical-mechanical integrated analysis to obtain the optical performance of the system. In this dissertation, the basic theory of finite element method in structural analysis is introduced. And the material properties commonly used in spaceborne optomechanical systems are introduced. For the integrated optomechanical analysis of the system, the results obtained by finite element simulation analysis are discrete node displacements data. While in the field of optical design and analysis, the model is established by mathematical description. The optical surface is defined by the relative position from the others and the surface type parameters. Therefore, the result of the finite element analysis is needed to be processed when it is transmitted between disciplines. This dissertation focuses on the method of separating point cloud data obtained by finite element simulation analysis into two parts: rigid body displacement and elastic deformation of an optical surface. The rigid body displacement of the optical surface is calculated by the homogeneous coordinate transformation. And the residual deformation error is fitted to the universal used Zernike polynomial in the optical model. So that the result of the finite element analysis of the optomechanical system can be transmitted to the optical model. This program for interdisciplinary integration of simulation result data has been designed. Thus errors caused by manual operation of large amounts of data can be avoided. The homogeneous coordinate transformation algorithm and Zernike fitting algorithm are discussed in terms of accuracy. Based on these, the modeling methods of optical components in the process of integrated optomechanical analysis are discussed. The main methods are single-point model, two-dimensional shell model and three-dimensional solid model. For lightweight mirrors, it can be simplified by equivalent stiffness model. The three-dimensional thin shell model is a more accurate model of the lightweight mirror. Finally, the deviation of the boresight accuracy of the spaceborne lidar is analyzed under the condition of gravity unloading, the temperature gradient of the receiving telescope, the temperature gradient of the secondary mirror support, and the temperature gradient of the standard optical deck. The analysis results are used for thermal design of the spaceborne lidar. Two cases of vertical and parallel receiving telescope optical axis of gravitational unloading were analyzed. The results showed that in the direction of the vertical axis, the maximum misalignment between the transmitter optical axis and the receiver optical axis will be 152.67 μrad. The maximum axis misalignment is 58.12 μrad in the parallel axis gravity unloading. The analysis of the key components of the receiver system shows that when the temperature deviation within the receiving telesocope primary mirror surface is 2 °C, the deviation of the receiving and emitting axis is 0.2 μrad. If the secondary mirror supporting barrel have a temperature difference of 2 °C in the vertical direction, the maximum misalignment deviation is 9.6 μrad. The optical standard board is the key component, and the maximum misalignment deviation caused by a temperature difference of 2 °C in the direction of the vertical axis is 16.44 μrad. And the maximum deviation caused by a radial temperature difference of 2 °C is 37.32 μrad. Finally, combined with the thermal control design of the system and the on-orbit working environment, a comprehensive analysis of the spaceborne lidar is conducted. In the harsh environment of the orbit, the misalignment of the boresight is 98.33 μrad, and the signal to noise ratio is decreased with 82.6 percent. The misalignment angle could be adjusted by the beam steering mirror. |
| 学科主题 | 光学工程 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31116]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 穆永吉. 星载大气激光雷达光机集成分析的研究[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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