大气湍流格林伍德频率测量方法的研究

	大气湍流格林伍德频率测量方法的研究
	瞿青
学位类型	硕士
导师	曹召良
	2014-11
学位授予单位	中国科学院大学
学位专业	光学
关键词	大气湍流格林伍德频率位相差值法波前重构
摘要	大气湍流的特性是大口径地基望远镜选址和自适应光学系统设计的基本依据。大气相干长度和格林伍德频率是描述大气湍流时空特性的两个基本参数，因此须研究大气相干长度和格林伍德频率的测量方法。目前，测量大气相干长度的方法已经比较成熟，而格林伍德频率的测量尚不完善。因此，本论文主要针对格林伍德频率的准确测量进行研究，以期为望远镜选址和自适应系统设计提供直接依据。针对位相差值法测量格林伍德频率存在的测量精度低、无测量参数设定依据等问题，本论文进行了高精度波前重构、哈特曼探测噪声消除、多个测量参数对测量精度影响分析等研究工作。提出一种适用于任意面形波面的区域高精度、高速重构方法。把波面形状信息耦合到几何矩阵中，实现对斜率矩阵的约束，从而大大提高了任意面形波面重构精度。和传统的波前重构方法相比，重构误差的RMS值从0.095λ降低到0.003λ，重构精度提升30倍。和迭代法相比，二者精度一致，但是计算速度提高3倍。同时研究了有效采样点数和采样密度对波前重构精度影响，结果显示，对5λ的环形波面，当有效采样点数增加到600后，才对重构精度无影响；当采样密度增加到65时，才对重构精度无影响。该工作为大气湍流格林伍德频率测量提供高精度位相波前，为高精度高精度测量格林伍德频率提供必备条件。研究了哈特曼探测器测量噪声的消除方法，根据斜率差与测量噪声之间的关系，去除重构位相结构函数中的噪声项，获得原始位相结构函数，再采用位相差值法公式对格林伍德频率计算。通过实验对格林伍德频率为62Hz的湍流进行了测量，去除噪声前后测量值分别为80Hz和61.5Hz；去除噪声后，测量值的偏离量从30%降低到0.6%，大大提高了测量精度。定量分析了测量参数对大气湍流格林伍德频率测量精度的影响：利用大气湍流模拟器产生不同频率的大气湍流，利用哈特曼探测器进行测量和分析，结果显示，当光斑大小为3?3像素、波面采样点数为400、统计次数为400次时，可以实现格林伍德频稳定精确的率测量。研究了格林伍德频率和最大允许采样时间的关系,得到了不同格林伍德频率对应的最大采样时间。结果显示，湍流越弱，可容许的最大采样时间越长，反而反之。同时，对最大采样时间和格林伍德频率的离散数值点进行拟合，获得了经验公式，为测量大气湍流格林伍德频率采样时间的选取提供依据。利用波面位相结构函数与采样时间之间的关系，获得了大气湍流格林伍德频率与哈特曼探测器最大采样时间的经验公式，为哈特曼探测器帧频的选取提供依据。最后，针对频率8Hz-108Hz的湍流进行测量，结果显示，当湍流频率大于62Hz时，测量值与理论值基本重合；当频率小于62Hz时，由室内空气存在约2Hz的低频扰动，使得得格林伍德频率测量值与理论值相差约1-2Hz，且频率越高误差越小。该扰动在室外测量时便不存在，因此可以认为实现了格林伍德频率的准确测量。总之，本论文利用高精度的波前重构方法、哈特曼探测器噪声消除方法以及合适的选取各个测量参数，最终实现了大气湍流格林伍德频率的准确测量。该研究工作为格林伍德频率的测量提供理论和应用指导意义，从而为望远镜站址选取和自适应光学系统的设计提供基本依据。
其他摘要	Characteristics of atmospheric turbulence is the fundamental basis for the siting of large-diameter ground-based telescope and the design of adaptive optical system. The atmospheric coherence length and Greenwood frequency is the two critical parameters for describing the characteristics of atmospheric turbulence, so their measurement methods need to be studied. Currently, the method of measuring atmospheric coherence length is relatively mature, but it is not good for the measurement of Greenwood frequency. Therefore, this thesis is researched on the accurate measurement of Greenwood frequency to provide a direct basis for the siting of large-diameter telescope and the design of adaptive optical system. As the problems of the phase difference method, such as that the measurement accuracy of Greenwood frequency is very low, and it doesn’t consider the measurement parameters and so on. Some works are conducted in this paper to solve the problems. Firstly it proposed an high accuracy and speed reconstruction method for arbitrary shape wave-front. By coupling the information of wave-front shape to the geometry matrix, it greatly improves the reconstruction accuracy. Compared to traditional wave-front reconstruction method and iterative method, the reconstruction accuracy increased 30 times and the calculation speed increased 3 times respectively. Secondly the impact of effective sampling points and the sampling density on wave-front reconstruction accuracy have been studied, the results show that for the annular wave-front with 5λ magnitude, when the effective sampling points and sampling density increases600 and 65 respectively, it had no effect on the reconstruction accuracy, which provides necessary conditions for the measurement of atmospheric turbulence Greenwood frequency accurately. Thirdly it studied the removing method of noise in the Hartmann detector. For the turbulence of 62Hz, the measurement deviation decreased from 30% to 0.6% by removing the noise, which greatly improved the measurement accuracy. And the effects of measurement parameters on the measurement accuracy of Greenwood frequency is analyzed, when the spot size is 3′3 pixels , sampling points and the statistical number are 400, the stable and accurate measurements can be achieved. Then it studied the relationship between the Greenwood frequency and its maximum sampling time, and get the empirical formula，which provides an basis for the selection for the frame rate of Hartmann detector. Finally, the turbulence of 8Hz-108Hz is measured, the results show that the measured value is almost the same as theoretical value without consideration of the disturbance of the air in the Lab. As the disturbance would not exist when it measures the Greenwood frequency outside, it is considered to achieve an accurate measurement of Greenwood frequency. In summary, this thesis ultimately achieve the accurate measurements of Greenwood frequency of atmospheric turbulence with the high precision wave-front reconstruction method, the Hartmann detector noise cancellation method and the appropriate selection of various measurement parameters, which provide theoretical and practical significance for the measurement of Greenwood frequency, and provide the fundamental basis for site selection of telescope and design of adaptive optics systems.
语种	中文
文献类型	学位论文
条目标识符	http://ir.ciomp.ac.cn/handle/181722/44680
专题	中科院长春光机所知识产出
推荐引用方式 GB/T 7714	瞿青. 大气湍流格林伍德频率测量方法的研究[D]. 中国科学院大学,2014.

条目包含的文件
文件名称/大小	文献类型	版本类型	开放类型	使用许可
瞿青.pdf（6006KB）			开放获取	ODC PDDL	请求全文