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题名:
基于相位差法的高分辨率成像和望远镜像差检测技术
作者: 李强
学位类别: 博士
答辩日期: 2007-06-07
授予单位: 中国科学院光电技术研究所
授予地点: 光电技术研究所
导师: 沈忙作
关键词: 大气湍流 ; 望远镜像差 ; 图像复原 ; 相位差法 ; 优化 ; 大气湍流模拟器 ; 扩展目标模拟器
其他题名: High Resolution Imaging and Measurement of telescope aberration using Phase diversity
学位专业: 光学工程
中文摘要: 当光波在大气中传播时,由于大气湍流引起的折射率的随机变化,光束的波前会发生畸变。对于地基大型望远镜而言,大气湍流使得目标成像模糊、光能分散、分辨力严重下降。目前,国内外科研工作者已经开展了多年的工作,致力于研究克服大气湍流的事后图像复原技术。现阶段,比较有效的事后图像复原方法有斑点成像、盲反卷积、反卷积和相位差法等。 相位差法是一种典型的事后图像处理方法,该方法利用在焦面上和离焦量面上同时采集的短曝光图像,在复原湍流退化图像的同时,还可以估计出大气湍流和望远镜像差引入的波前相位畸变。本论文在统计信号估计、最优化理论的基础上推导和分析了利用相位差法进行图像盲复原的基本算法,并使用适合于大规模优化的的有限内存BFGS法对图像复原问题进行了求解。我们先后使用相位差法复原了计算机模拟的大气湍流退化图像、实验室模拟湍流退化图像、瑞典SVST望远镜太阳表面结构观测图像和云南天文台1.2m望远镜单星观测图像。利用计算机模拟的湍流退化图像,我们对几个影响相位差法复原性能和效果的因素进行了详细地研究,主要包括优化算法的选择、图像帧数等因素。我们对只使用单通道焦面图像、单通道离焦图像和相位差法的复原性能进行了比较,结果表明相位差法比仅仅使用单通道图像的算法复原效果更好。大量的实验结果证明,相位差法能够有效地克服大气湍流的影响,实现点目标和扩展目标的高分辨成像。 为了更方便的对相位差法等湍流退化图像复原算法进行深入地研究,我们设计和建立了大气湍流退化图像实验室模拟系统,该系统主要由扩展目标模拟器、大气-望远镜成像系统和双路图像采集系统三个部分构成。在实验中,我们使用液晶光阀实现了扩展目标的模拟,使用步进电机驱动三块随机相位板来模拟大气湍流效应,实现了双通道图像同步采集。大气湍流退化图像实验室模拟装置的建立,不仅仅为验证相位差法的正确性提供了有效的数据,而且还能为斑点成像、盲反卷积等图像复原算法的研究提供实验数据。 对于地基大型光学望远镜而言,除了大气湍流的动态扰动外,光学元件的加工误差、光学设施的装调误差、望远镜内部温度不均匀和重力变形等因素也会使入射光束的波前发生畸变,导致望远镜的分辨能力严重下降。因此,如何在天文台现场准确地测量望远镜的像差,是进一步提高望远镜分辨能力的关键问题。在本论文的研究工作中,我们提出使用相位差法恢复出望远镜光瞳上波前相位的瞬时分布,然后根据大气湍流的统计特性进行平均,实现对望远镜像差的估计。通过计算机模拟实验,对利用相位差法恢复光瞳上的波前相位和测量望远镜像差进行了研究。模拟研究结果表明,利用相位差法能够有效地估计出望远镜像差。
英文摘要: As light propagates through the atmosphere, light rays are distorted due to random variations in the index of refraction caused by atmospheric turbulence. This causes degradation of the images of astronomical object captured with a ground-based telescope. A variety of image restoration approaches have been developed to reduce or remove the turbulence-induced blurring. These approaches include speckle imaging, blind deconvolution, deconvolution with wavefront sensing, and phase diversity. Phase diversity is an effective post-processing method that can be used to overcome the turbulence-induced degradation. The method uses an ensemble of short-exposure images obtained simultaneously from multiple cameras to jointly estimate the object and the wavefront distribution on pupil. One of these images is the focal-plane image that has been degraded by unknown aberration, such as turbulence and telescope aberration. The other of these images is collected in a separate channel that is formed by further blurring the focal-image in some known fashion, such as by adding defocus. Based on signal estimation theory and optimization theory, we have derived the cost function of phase diversity method and solved the large-scale optimization problem using a limited memory BFGS (Broyden-Fletcher–Goldfarb-Shanno) algorithm. We have applied the method to the turbulence-degraded images generated with computer, the images collected in our simulation system of turbulence-degraded image, the solar images acquired with the Swedish Vacuum Solar telescope (SVST, 0.475 meters) in La Palma and the star images collected with 1.2-meters telescope in Yunnan Observatory. Using the turbulence-degrade images generated with computer; we have studied several factors that influenced the performance of phase diversity algorithm, such as different optimization algorithm, frame numbers, defocus distance, and so on. We have also compared the result restored by single-channel-focus images, single-channel-defocus images and dual-channel images. The restoring results demonstrate that the phase-diversity method is remarkably efficient for removing the effect of atmospheric turbulence and solving the image restoration problem of extended object. In order to study phase diversity method and other image restoration algorithm, we have established a simulator of turbulence-degraded image in laboratory. This system is constituted of three parts, including the extended object simulator, the turbulence simulator and the dual-channel image acquired system. In experiment, we have used LCLV (Liquid Crystal Light Value) to simulate the extended object and three random phase screen derived by step-servo motor to simulate dynamical turbulence. The turbulence-degraded images simulated in laboratory can provide sufficient data for the study of phase diversity, speckle imaging and blind deconvolution. The images recorded by a ground-based telescope are not only degraded by atmospheric turbulence, but also by the imperfections of optical elements, optical misalignment and the mirror distortion caused by gravity. The atmospheric turbulence varies dynamically and the telescope aberrations are static or vary slowly. For measuring the telescope aberrations with the disturbance of atmospheric turbulence, we have developed a method based on phase-diversity technique. Using phase-diversity method, we can independently reconstruct many instantaneous wavefront from pairs of simultaneously recorded focused and defocused images. After that, by averaging these reconstructed wavefront, the telescope aberrations are separated from dynamic wavefront induced by turbulence. The computer simulation of estimation of telescope aberration using phase-diversity method is conducted. The results show phase-diversity method can estimate the telescope aberrations effectively and root-mean-square error is about 0.08 wavelengths
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ioe.ac.cn/handle/181551/213
Appears in Collections:光电技术研究所博硕士论文_学位论文

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Recommended Citation:
李强. 基于相位差法的高分辨率成像和望远镜像差检测技术[D]. 光电技术研究所. 中国科学院光电技术研究所. 2007.
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