1m新真空太阳望远镜成像系统观测数据干涉条纹特性分析及消除方法

发布时间：2018-03-03 16:24

本文选题：仪器　切入点：探测器　出处：《天文学报》2016年05期 　论文类型：期刊论文

【摘要】：抚仙湖1 m新真空太阳望远镜(New Vacuum Solar Telescope,简称NVST)是我国新一代地基太阳观测设备之一,其中Hα成像系统是进行太阳色球观测的主要终端.实测Hα观测数据(特别是偏带观测数据)中明显存在由薄膜干涉引起的等厚条纹,而常规平场校正有时无法将其消除,并在后期图像高分辨率重建过程中造成严重影响.为了解决这个问题,利用连续4 h的Hα偏带观测数据对干涉条纹的空间和时间分布特性做了分析并发现:干涉条纹的间距或二维空间分布样式随时间固定不变,但条纹的强度随时间变化明显(4 h左右可见度增加9倍),是导致常规平场校正无法将其消除的主要原因.由此推断造成上述时变特性的主要原因是观测过程中入射光的强度以及入射光与CCD靶面位置的相对角度随时间发生了变化,而且产生条纹的薄膜结构与靶面位置距离较近.尝试了两种降低条纹可见度的方法.首先对探测器(pco.4000型CCD)光敏介质的前封窗进行了改造,通过改造前封窗楔角至2?的方案来调制条纹间距至CCD像元尺度,改造之后小范围视场内可识别出可见度仅为0.6%的少量干涉条纹.其次基于图像滤波技术提取干涉条纹图样并生成所谓条纹平场,分别采用和比较了频域傅里叶变换滤波和空域中值滤波两种方法,结果基本相同.观测数据再次进行条纹平场校正之后,条纹消除效果明显:可见度可降低8倍左右(即由之前的4.7%降低为0.6%以下).同时也指出多幅图像的积分(累加)可以有效降低精细太阳结构在条纹平场提取中的影响,并给出累加时间的经验值约为20 min.
[Abstract]:New Vacuum Solar Telescope1 m vacuum Solar Telescope in Fuxian Lake is one of the new generation of ground-based solar observation equipment in China. The H 伪 imaging system is the main terminal of the solar color sphere observation. There are obvious equal-thickness fringes caused by thin film interference in the observed H 伪 observation data (especially the biased band observation data), which can not be eliminated by conventional flat field correction. In order to solve the problem, The spatial and temporal distribution characteristics of interference fringes are analyzed by using the H 伪 bias band observation data for 4 hours. It is found that the spacing of interference fringes or the spatial distribution patterns of two dimensional interference fringes are fixed with time. However, the intensity of the stripe increases nine times with time, which is the main reason that the conventional flat-field correction can not eliminate it. It is concluded that the main reason for the time-varying characteristics is the input into the observation process. The intensity of the incident light and the relative angle between the incident light and the target surface of CCD vary with time. Two methods to reduce the visibility of the stripe are tried. Firstly, the front sealing window of the detector type CCD-4000) Guang Min is modified, and the front sealing window of the former sealing window is modified to 2? 2 by the transformation of the front sealing window of the film structure which produces the stripes and the location of the target surface is close to that of the target surface, and two methods are tried to reduce the visibility of the stripe. The scheme modulates the fringe spacing to the CCD pixel scale, and after the transformation, a small number of interference fringes whose visibility is only 0.6% can be identified in the small field of view. Secondly, the interference fringe pattern is extracted based on the image filtering technique and the so-called fringe flat field is generated. Fourier transform filtering in frequency domain and median filtering in spatial domain are adopted and compared, respectively, and the results are basically the same. The effect of stripe elimination is obvious: the visibility can be reduced by about 8 times (that is, from the previous 4.7% to less than 0.6%). At the same time, it is pointed out that the integration (accumulation) of multiple images can effectively reduce the influence of fine solar structure on the extraction of the fringe flat field. The empirical value of accumulated time is about 20 mins.
【作者单位】：中国科学院云南天文台;中国科学院大学;
【基金】：国家自然科学基金项目(11473064) 中国科学院基础局物质科学前沿与交叉项目资助
【分类号】：P111.41

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