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激光导引星波前倾斜测量问题是限制自适应光学技术在天文领域广泛应用的关键问题之一。测量并改正激光上行到达角起伏是解决这一问题的有效方法。提出一种基于统计平均算法而不依赖自然导引星和辅助望远镜的测量方法,可以有效地测量出激光上行到达角起伏。利用具有子孔径阵列的哈特曼波前传感器对激光信标进行探测,选择部分子孔径进行倾斜量的统计平均以获得激光上行到达角起伏。仿真了统计平均算法的误差随子孔径数量的变化关系。结果表明,最小算法误差相对于望远镜全口径倾斜误差的下降比例与大气相干长度无关,而与望远镜口径有关。望远镜口径越大,算法误差相对于全口径倾斜误差下降越多。当望远镜口径为10 m时,最小算法误差下降为望远镜全口径倾斜误差的33%。 相似文献
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波前检测是天文望远镜自适应光学中的重要环节。四棱锥作为一种新型的波前检测元件,与其他传统的波前传感器相比,具有较高的灵敏度。特别是对于光干涉或拼接镜面望远镜而言,四棱锥波前传感器能够被用来检测子望远镜或子镜面之间的相对光程差,从而为干涉(或共相)的实现提供有效的检测信号。在分析四棱锥波前检测原理的基础上,阐述了单孔径条件下波前倾斜检测及双孔径干涉条件下相对光程差检测的软件仿真设计和阶段性成果,并简述了下一阶段的研究计划。 相似文献
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为检测云南天文台１．２ｍ望远镜光学成像质量,在多种光学检测方法中,我们结合实际情况,详细地讨论了两种方案的可能性。并用美国ＺＥＭＡＸ光学设计软件设计了所需的光学辅助元件。第一种方案,将全口径分割成直径为３００ｍｍ的子孔径后,利用哈特曼传感器对每个子孔径的最后成像波面进行探测,得到波前畸变量。最后将所得到的子孔径波面合成得到全口径波面,进而分析系统成像质量。第二种方案采用补偿干涉法,利用设计的补偿器补偿主镜的法线象差,得到干涉条纹,再由干涉条纹分析得到主镜面形差。这两种方法都实现微机实时采样与处理,能以较快速度计算出最后结果。最后,我们讨论了检测过程中误差来源及精度分析。在实验条件满足的情况下,整个系统的测试精度优于λ／１０。 相似文献
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基于相位差方法的天文目标高分辨率成像,是利用在焦面和离焦位置上同时采集的一对或者多对短曝光图像,对目标和大气湍流引入的波前相位分布进行估计．在计算机模拟望远镜成像系统和相位差方法图像采集过程的基础上,利用信号估计和最优化理论,确定了高斯噪声模型下的目标函数,采用适合于大规模无约束优化的有限内存拟牛顿法对图像恢复问题进行了数值求解．恢复结果表明,基于相位差方法的高分辨成像技术,可以有效地克服大气湍流的影响,解决天文扩展目标的图像恢复问题． 相似文献
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《天文研究与技术》2016,(3)
利用组成星座的小卫星,分别携带分离的子望远镜和合光成像望远镜,构成Fizeau型光学综合孔径干涉系统,实现高分辨率的面源目标成像是当前的研究热点之一。这种光干涉成像系统,由于稀疏度较大,UV覆盖不全,即空间频率采样不连续,表现为系统光学传递函数有零值存在。要克服UV覆盖不全的影响,获得等效的大孔径望远镜成像效果,需要改变子孔径的空间排布,获得不同基线条件下的图像,进行空间频率信息的提取和合成,最后采用逆滤波的方法达到提高图像质量的目的。在分析单子孔径传递函数与系统传递函数关系的基础上,优化子孔径的排布方式,采用不同的频域滤波器将不同基线获得的图像中信噪比高的频率区域提取出来进行合成,再变换到空域并进行逆滤波处理,得到改善的合成图像。仿真结果显示,当得到的干涉图信噪比较低时,该方法可以有效地提高合成图像的质量。 相似文献
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《天文研究与技术》2017,(3)
消除综合孔径望远镜子孔径之间的相对光程差是实现高分辨率干涉成像的前提条件,条纹检测法是一种检测相对光程差的有效办法。因子孔径的空间位置排布使干涉条纹具有一定的方向性,若不能精确获知干涉条纹的角度,则无法沿条纹的法线方向行采样,进而无法根据对比度变化曲线的最大值获得子孔径之间的最小光程差位置。提出了一种基于傅里叶变换和图像二值化阈值遍历的获得干涉条纹角度的方法,首先介绍了算法的基本原理,其次通过对条纹角度为43°的仿真数据进行算法验证得到的角度为43.007 8°,与理论值的误差为0.018%,证实了方法的可行性。最后对比了未旋转相机和旋转相机两种情况下的条纹对比度变化曲线,可知通过旋转相机使条纹转至相机靶面纵轴方向再进行采样的办法,更有利于精确得到相对光程差的最小位置。 相似文献
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菲索型光干涉望远镜得到高分辨率成像的关键是消除各子镜之间相位平移误差。宽光谱条纹对比度检测法是一种检测相位平移误差的有效办法。基于物理光学的基本原理,论证了平移误差与系统点扩展函数的关系,进而仿真了共相远场条纹像,分析了共相检测与控制过程和数据预处理的方法,提出了加权对比度的算法和共相维持的方法,最终得到了共相远场像,并与仿真结果进行了对比。结果表明,实验与仿真的共相远场像能量分布形态以及数值都比较接近,该方法可以实现对子镜之间相位平移误差的检测与控制。 相似文献
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为检测云南天文台１．２ｍ望远光学成像质量,在多种光学检测方法中,我们结合实际情况,详细地讨论了两种方案的可能性,并用美国ＺＥＭＡＸ光学设计软件设计了所需的光学辅助元件,第一种方案,将全口径分割成直径为３００ｍｍ的子孔径后,利用哈特曼传感器对每个子孔径的最后成像波面进行探测,得到波前畸变量,最后将所得到的子孔径波面合成得到全口径波面。进而分析系统成像质量。第二种方案采用补偿干涉仪,利用设计的补偿器补 相似文献
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分别对Hinode光学望远镜SOT观测太阳黑子的本影和半影图像以及太阳米粒组织图像进行了空间频谱计算和相关计算,分析了太阳不同结构区域图像的时域和空域特性对哈特曼波前探测精度的影响。计算和分析结果表明,在子孔径波面倾斜小于0.25″情况下,米粒组织图像采样时间在2 min内、本影和半影采样时间在4 min内,对子孔径波面倾斜探测精度的影响极小;并且由太阳目标特性引起的哈特曼波面探测误差随波面畸变量的增大而增大。这些研究结果可为太阳望远镜哈特曼波前探测器研制和应用提供依据和参考。 相似文献
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A novel design for a giant Arecibo-type spherical radio telescope with an active main reflector 总被引：8，自引：0，他引：8
Yuhai H. Qiu 《Monthly notices of the Royal Astronomical Society》1998,301(3):827-830
A novel design for a giant spherical radio telescope is proposed. Instead of a fixed spherical reflecting surface such as with the 305-m Arecibo telescope, the illuminated portion of the reflecting surface is made to fit a paraboloid of revolution in real time by active control. A simple feed can thus be used, enabling the realization of broad bandwidth and full polarization. The actual design utilizes a karst depression which gives a spherical surface of 300-m radius, having an opening of 500-m diameter. The illuminated aperture is chosen to be 300 m, and the focal ratio is 0.46–0.48. With this geometry and the simple feeding system, a giant telescope with large sky coverage can be achieved at low cost. When the illuminated aperture is limited to 70–100 m, the area trackable can be extended to about 10° above the horizon. 相似文献
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闭合相位技术、U -V覆盖技术和像重构技术是光学综合孔径干涉成像的三个关键技术。文中简要介绍了光学综合孔径技术的发展历史、这三种关键技术和光学综合孔径望远镜阵的构成 ,对之进行了多光束干涉的计算机仿真和实验仿真 ,两者结果一致说明了光学综合孔径干涉成像技术中有关干涉的理论的正确性 ,指出了下一步的研究方向。 相似文献
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The Low Frequency array (LOFAR) will be a next generation digital aperture synthesis radio telescope covering the frequency range from 10 to 240 MHz. The instrument will feature full polarisation and multi-beaming capability, and is currently in its design phase. This work highlights the solar, heliospheric and space weather applications where LOFAR, with its unique and unprecedented capabilities, can provide useful information inaccessible by any other means. The relevant aspects of the LOFAR baseline design are described, and the most promising techniques of interest are enumerated. These include tracking coronal mass ejections (CMEs) out to large distances using interplanetary scintillation (IPS) methods, tomographic reconstruction of the solar wind in the inner heliosphere using IPS, direct imaging of the radio emission from CMEs and finally possible Faraday rotation studies of the magnetic field structure of the heliosphere and the CMEs. This work is a part of an effort directed towards ensuring the compatibility of LOFAR design with solar and space weather applications, in collaboration with the wider community. 相似文献
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《天文和天体物理学研究(英文版)》2020,(1)
This paper proposes an active sub-reflector suitable for large radio telescopes, which can compensate both of the deformation of the main reflector and sub-reflector position offsets. The mathematical formula of the main reflector deformation compensated by the sub-reflector is deduced based on Cassegrain and Gregory antenna structures. The position of the sub-reflector is adjustable to compensate for defocusing errors on high and low elevations, which are mainly caused by the deformation of the sub-reflector supporting legs. In this paper, the method of obtaining the optimum position of the sub-reflector from the aperture phase by the interferometric method is introduced. The actual measurement is verified on the Tianma 65 m radio telescope, which provides a new way to diagnose the position error of the sub-reflector. 相似文献
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Richard Dekany Roger Angel Keith Hege Dave Wittman 《Astrophysics and Space Science》1994,212(1-2):299-319
Traditional astrometric methods are limited in accuracy by the atmosphere in a way that does not show much improvement with increased telescope aperture. However, there is the potential for very high accuracy with large telescopes if advantage can be taken of these factors: First, the differential atmospheric distortion of images of closely adjacent stars is less with larger aperture; second, the diffraction limit is sharper, and third, photon statistics are improved. In this paper we analyze and give experimental tests of techniques that could be applied to the detection of planets with the mass of Jupiter or Uranus, if they are present in nearby binary star systems.The atmospheric perturbation of the relative position of the energy centroids measured in short exposure images of binary stars depends on the effective height of the turbulent distortion. For a 4-meter telescope, the error in centroid determination of a 4-arcsec binary can be as small as 20 milliarcsec (mas) in a single 20-millisecond (msec) exposure. The relative position measured by cross-correlation of short exposure speckle images, as suggested by McAlister (1977b), may give even higher accuracy. In this case, Roddier (Roddieret al., 1980) has shown that the atmospheric error depends on the thickness rather than the height of the layers that make the dominant contribution to the turbulence. Through Monte Carlo analysis we show that on occasions when the turbulence arises largely in a thin layer, a single 20-msec exposure of a 4-arcsec binary taken with a 4-m aperture can yield an astrometric accuracy of order 0.5 mas.We report on experiments made at the Steward Observatory 2.3-m telescope which achieved accuracies corresponding to 1.7 mas in a 2.24-arcsec binary and 16.1 mas in a 6.0-arcsec binary with only 15 and 18 specklegram pairs respectively. We plan to use the 6.5-m converted MMT to obtain much higher performance, between 4.0 mas and 0.40 masper independent specklegram pair, depending upon atmospheric conditions, for binaries of 4-arcsec separation. By cycling rapidly through perhaps 100 binaries, thus calibrating systematic errors through the average change in binary separation, Jupiter-mass planets may be detectable with small but regular access to the telescope.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
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大口径望远镜受大气湍流的影响,光学分辨率远远小于其自身光路所决定的衍射极限。为了相应的自适应光学系统设计,首先有必要对大气波动进行仿真以提供环境数据。通常的大气波前仿真方法需要通过计算结构函数,得到功率谱函数,进而得到仿真波前,但该方法存在计算速度慢,中间变量存储空间大的问题,给大口径望远镜或者长时间仿真带来很大不便。介绍了一种可行的基于迭代分形法的波前仿真方法,复杂度达到O（N）,可以大大提高波前仿真的速度。 相似文献
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Jiang Shi-yang 《Chinese Astronomy and Astrophysics》1981,5(3):373-375
Because of the limitations both from the slit width and the slit length of the spectrograph used in high resolution work, the efficiency of a telescope, with an aperture between D0 = 9m and D′0 = 55m, will be no better than that of a telescope with aperture D0. D0 can be identified as the maximum aperture of a ground-based telescope. 相似文献
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V. Yu. Terebizh 《Experimental Astronomy》2001,11(3):171-191
An exact analytical procedure is described for the optimum design of baffles for any Cassegrain telescope with conicoid type mirrors. Here, `optimum' means the least obstruction coefficient given perfect blocking of direct light by baffles. The corresponding algorithm is based on the ray-tracing formulas in a two-mirror telescope with arbitrary position of the aperture stop. The optimal configuration of baffles is unique. The dependence of the obstruction coefficient upon the telescope characteristics is studied. The optical system can be designed in such a way that the obstruction is equal to a predefined value. As examples, the Hubble Space Telescope and the Ritchey–Chretien system with the obstruction coefficient 0.25 are considered. 相似文献
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Our main goal is to determine the dynamic equations of a certain complex system, as is the case of the mechanical system for
a small aperture telescope. Causes of this complexity are: the lack of documents about the operation of the elements belonging
to the system, and the variation of dynamics with respect to the time and the position of the telescope. To check that we
have obtained a valid set of dynamic equations, we will design a computer control system that will implement a self-guide
system for the telescope.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献