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激光导引星波前倾斜量测量方法的研究
Alternative TitleStudy on the Methods of Tip-tilt Measurement with a Laser Guide Star
黄凯
Subtype博士
Thesis Advisor熊耀恒
2015-07-01
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline天体测量与天体力学
Keyword激光导引星 波前倾斜 自适应光学 大气湍流 Zernike多项式
Abstract自适应光学技术经过多年发展已经成功应用于多个研究领域。在天文应用中,由于夜天文目标本身较暗,所以需要人造信标为自适应光学系统提供波前探测。激光导引星是目前广泛应用的人造信标,但是由于激光在极短时间内上下两次通过大气湍流,导致其波前倾斜难以准确探测,而只能利用目标附近足够亮度的恒星作为倾斜探测信标。该问题限制了现有激光导引星自适应光学系统在天文观测中的目标覆盖率。 本论文针对人造激光导引星波前倾斜难以测量的问题,从理论上分析了大气湍流倾斜非等晕特性,设计了辅助望远镜波前倾斜测量方案,并利用云南天文台1.2m 望远镜及25cm 辅助望远镜对激光导引星波前倾斜测量方法进行了实验验证,证明了利用辅助望远镜对激光导引星波前倾斜测量的可行性,文章提出了一种基于子孔径探测的波前倾斜测量方法,为将来大口径望远镜激光导引星波前倾斜测量提供了一种实用性的测量手段。 本文旨在通过对激光导引星波前倾斜探测的研究探寻一种可以用于实际观测的激光导引星波前倾斜测量方法。在理论研究方面,本文利用Zernike 多项式波前像差模式分解的方法,推导了辅助望远镜视场内激光拖影的任意两点之间的倾斜相关函数,考虑了激光带不同点之间的海拔差异,分析了大气湍流强度、激光带任意两点之间的海拔差、接收望远镜口径等对倾斜相关函数的影响,为激光导引星波前倾斜测量方案的分析和设计提供了理论基础。本文建立了激光发射系统的一般几何模型,分析了激光发射光路与目标接收光路的倾斜相关性,得到了激光导引星波前倾斜难以探测的本质并不是激光上行和下行波前倾斜的相互抵消,而是激光上行光路大气湍流对激光导引星整体倾斜的干扰。该结论为激光导引星波前倾斜测量方案的设计提供了技术思路。 在波前倾斜测量方法研究方面,本文以Belen’Kii提出的统计平均原理为基础,系统地分析了辅助望远镜波前倾斜测量方法,首次给出了利用辅助望远镜对任意指向激光导引星整体倾斜进行测量的重构函数,从而证明了使用两台辅助望远镜就能够探测任意激光指向的整体波前倾斜,而不仅仅局限于天顶附近的指向。 在实验研究方面,本文利用云南天文台现有条件,设计了一套Rayleigh激光导引星波前倾斜测量验证实验,以1.2m 望远镜为主望远镜,25cm望远镜为辅助望远镜,完成了对激光导引星波前倾斜测量的实验研究;利用辅助望远镜得到的波前倾斜信息,通过事后处理的方式对主望远镜探测的恒星目标进行了倾斜校正,校正残余误差达到RMS=0.3arcsec;验证了辅助望远镜对激光导引星波前倾斜测量方法的可行性。实验中,本文首次提出了实时拍摄阈值背景图的数据处理方法,解决了低亮度扩展人造目标的数据处理问题。本文首次公开报道了辅助望远镜对主望远镜发射的激光导引星随动指向的计算方法。 最后,本文总结了理论研究结果与实验研究经验,为进一步提高波前倾斜测量精度而提出了一种子孔径测量方法,以应用于将来大口径望远镜测量平台。 本文的研究意义在于:通过对激光导引星波前倾斜测量方法系统地研究,从理论上解释了激光导引星波前倾斜测量的本质,这是本文方法研究及实验设计的基础,也为将来提出应用于更多场合的激光导引星波前倾斜测量方案提供了理论支持;从实验上验证了利用辅助望远镜对激光导引星波前倾斜进行测量的可行性,为该技术实现工程应用提供了依据。本文有助于激光导引星波前倾斜测量难题的解决,这可以使天文暗弱目标的高分辨率探测成为可能,可以让天文学家对任意天区的任意目标进行高分辨率测量,可以让自适应光学技术应用于更多有价值的天文研究。
Other AbstractAdaptive optics technology has been successfully applied to many research fields. For astronomical applications, Adaptive optics systems require artificial beacon for providing wave-front measurements, due to the very dark object. Laser Guide Star(LGS) is widely used as an artificial beacon, but the tip-tilt of the wave-front is not measurable with a LGS, as a consequence of the round trip of the light. Thus only natural star near the observed object can be used to measure the wave-front tilt, which limits the sky coverage due to the probability to find star within the isoplastic patch of the object. This dissertation focuses on the problems of tip-tilt determination for LGS. At first, the tilt anisoplanatism of laser beacons caused by atmospheric turbulence is studied in theory. Secondly, the experiment scheme for tip-tilt measurement using auxiliary telescopes based on the 1.2m and 25cm telescope systems is designed and verified. In the end, a new tip-tilt determination technique with a laser guide star on large telescopes is proposed based on the idea of cross-shaped sub-apertures. This dissertation aims at exploring a practical way to solve the problem of tip-tilt determination with a LGS. In the aspect of the theoretical research, the Zernike coefficient correlations between two spherical waves coming from the LGS strip are derived. Effect of the atmospherical turbulence, difference of the altitude of LGS and size of the receiving telescope on the anisoplanatism of the LGS strip are analyzed, which is a theoretical foundation for the experiment design to measure a LGS's tip-tilt. In addition, a general geometrical model of laser transceiver system is established. Correlation between upward and downward optical path is analyzed with the model. It shows that the disturbances by the turbulence in the upward laser path is the key problem of tip-tilt determination in LGS system, which provides a technical principle for tip-tilt measurement with a LGS. In the aspect of measurement technology, a method of tip-tilt measurement with a LGS using auxiliary telescopes is systematically analyzes, based on the principle of statistical technique proposed by Belen’Kii. A transfer function is proposed first in the dissertation, which shows the relationship between the different tip-tilt from LGS and auxiliary telescopes. It proves that the sky coverage is close to 100%, when two auxiliary telescopes are used. In the aspect of experimental research, a verification experiment is accomplished at the site of Yunnan Observatories. This experiment arranged a 1.2m telescope to shoot laser and to detect a star at the same time. A 25cm telescope is arranged to detect the laser strip from 45m away as an auxiliary telescope. The jitter of star is corrected by the tilt signal from auxiliary telescope by post processing. An image processing method is reported to improve the signal to noise ratio(SNR) to a low-contrast laser beacon image. A calculation method of pointing a LGS with the auxiliary telescope is first presented in this dissertation. In the end of this dissertation, a new tip-tilt determination technique of laser guide star is proposed for a large telescope, based on both of the theoretical and experimental research. This dissertation revealed the nature of the tip-tilt determination problem in LGS system, and the feasibility of the tip-tilt determination for the LGS is verified with experimental research. The theoretical results provide support for further research about tip-tilt measurement for LGS. And the experimental results verified the feasibility of the new tip-tilt measurement method for LGS.
Subject Area天文学
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/9468
Collection应用天文研究组
Affiliation中国科学院云南天文台
Recommended Citation
GB/T 7714
黄凯. 激光导引星波前倾斜量测量方法的研究[D]. 北京. 中国科学院研究生院,2015.
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