【摘要】：中國科學(xué)院云南天文臺撫仙湖一米新真空太陽望遠鏡(New Vacuum Solar Telescope,簡稱NVST)是我國新一代地基太陽觀測設(shè)備之一,其中Hα成像系統(tǒng)是進行太陽色球觀測的主要終端。Hα實測數(shù)據(jù)(特別是偏帶觀測數(shù)據(jù))中明顯存在由薄膜干涉引起的等厚條紋,而常規(guī)平場校正有時無法將其消除,并在后期圖像高分辨率統(tǒng)計重建過程中造成嚴重影響,本論文便是針對成像系統(tǒng)的干涉條紋展開相關(guān)的特征分析和去除工作。論文首先介紹了天文薄型CCD產(chǎn)生干涉條紋的基本原理(即薄膜干涉),并可視化分析了薄膜厚度、入射角度以及折射率等參數(shù)對干涉條紋的影響。同時對NVST及其多波段成像系統(tǒng)進行了簡介,強調(diào)了望遠鏡各軸之間的旋轉(zhuǎn)不同心和鏡筒彎沉等對成像系統(tǒng)所造成的影響(例如入射角度的變化)。其次,集中分析了Hα偏帶觀測數(shù)據(jù)中干涉條紋的空間分布和時間演化特性。分析發(fā)現(xiàn):干涉條紋的間距或二維空間分布樣式隨時間固定不變,但條紋的強度隨時間變化明顯(4個小時左右可見度增加9倍),這是導(dǎo)致常規(guī)平場校正無法將其消除的主要原因。根據(jù)該現(xiàn)象,結(jié)合已有的光軸變化實測結(jié)果,推斷造成上述時變特性的主要原因是觀測過程中入射光的強度以及入射光與CCD靶面位置的相對角度隨時間發(fā)生了變化,而且產(chǎn)生條紋的薄膜結(jié)構(gòu)與靶面位置的距離比較近(應(yīng)在40mm以內(nèi)),為后續(xù)從硬件改造的角度抑制干涉條紋提供參考。在上述工作的基礎(chǔ)上,提出并嘗試了兩種降低條紋可見度的方法。首先對探測器(pco.4000型CCD)光敏介質(zhì)的前封窗進行了改造,通過改造前封窗楔角至2度的方案來調(diào)制條紋間距至CCD像元尺度,改造之后小范圍視場內(nèi)可識別出可見度僅為0.6%左右的少量干涉條紋。其次基于圖像濾波技術(shù)提取干涉條紋圖樣并生成所謂“條紋平場”,分別采用和比較了傅里葉頻域濾波、小波變換濾波和空域中值濾波三種方法,結(jié)果基本相同。觀測數(shù)據(jù)再次進行“條紋平場”校正之后,條紋消除效果明顯:可見度可降低8倍左右(即由之前的4.7%降低為0.6%以下)。同時也指出多幅圖像的積分(累加)可以有效降低精細太陽結(jié)構(gòu)在“條紋平場”提取中的影響,并給出累加時間的經(jīng)驗值約為15-20分鐘,為下一步的從高分辨統(tǒng)計重建算法角度抑制干涉條紋的工作提供了可借鑒的經(jīng)驗。最后討論了上述濾波方法的局限性,并嘗試利用Chae(2004)提出的新算法進一步減弱“條紋平場”中的太陽結(jié)構(gòu)痕跡。給出了該方法在NVST上的初步實測結(jié)果,為具有強對比結(jié)構(gòu)的活動區(qū)數(shù)據(jù)獲取“準實時平場”來修正干涉條紋提供了新的思路。
[Abstract]:The New vacuum Solar Telescope (New Vacuum Solar Telescope,) at Fuxian Lake, Yunnan Observatory, Chinese Academy of Sciences, is one of the new generation of ground-based solar observation equipment in China. The H 偽 imaging system is the main terminal of the solar color sphere observation. The equal-thickness fringes caused by thin film interference are obviously present in the H 偽 measured data (especially the biased band observation data), which can not be eliminated by conventional flat field correction. And in the process of high resolution statistical reconstruction of image, this paper is aimed at the interference fringes of the imaging system to carry out the relevant feature analysis and removal work. In this paper, the basic principle of interference fringes produced by astronomical thin CCD (thin film interference) is introduced, and the influence of thickness, incidence angle and refractive index on the interference fringes is analyzed visually. At the same time, the NVST and its multi-band imaging system are briefly introduced, and the influence of the different rotation center between the various axes of the telescope and the deflection of the mirror tube on the imaging system (such as the change of incidence angle) is emphasized. Secondly, the spatial distribution and temporal evolution of interference fringes in H 偽 biased band data are analyzed. It is found that the spacing of interference fringes or two-dimensional spatial distribution patterns are constant with time, but the intensity of fringes varies obviously with time (the visibility increases by 9 times in about 4 hours). This is the main reason that the conventional flat field correction can not be eliminated. According to this phenomenon, combined with the measured results of optical axis variation, the main reason for the time-varying characteristic is that the intensity of incident light and the relative angle between incident light and CCD target surface have changed with time. Moreover, the distance between the film structure and the target position is close (within 40mm), which provides a reference for further hardware transformation to suppress interference fringes. Based on the above work, two methods to reduce the visibility of stripes are proposed and tried. In this paper, the front sealing window of Guang Min medium of the detector (pco.4000 type CCD) is first modified. The fringe spacing is modulated to the size of CCD pixel by modifying the front sealing window with wedge angle to 2 degrees. A small number of interference fringes with a visibility of only 0.6% can be identified in the small field of view after the transformation. Secondly, the interference fringe pattern is extracted based on the image filtering technique and the so-called "fringe flat field" is generated. Three methods, Fourier frequency domain filtering, wavelet transform filtering and spatial median filtering, are adopted and compared, respectively, and the results are basically the same. After the "fringe flat field" correction is carried out again, the fringe elimination effect is obvious: the visibility can be reduced about 8 times (that is, from 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 "fringe flat field" extraction, and the empirical value of the accumulated time is about 15-20 minutes. It provides the experience for the next step to suppress interference fringes from the angle of high resolution statistical reconstruction algorithm. Finally, the limitations of the above filtering methods are discussed, and the new algorithm proposed by Chae (2004) is used to further weaken the trace of the solar structure in the "fringe flat field". The preliminary experimental results of the method on NVST are given, which provides a new idea for obtaining the "quasi-real-time flat field" from the active region data with strong contrast structure to correct the interference fringes.
【學(xué)位授予單位】：中國科學(xué)院研究生院(云南天文臺)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：P111.41

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1 彭仁軍,吳健;環(huán)狀干涉條紋成像技術(shù)的實驗研究[J];強激光與粒子束;2003年07期

2 刁其龍;黃春琳;;抑制穿過具有傾斜角度的介質(zhì)探測成像時產(chǎn)生的寄生干涉條紋現(xiàn)象[J];物理學(xué)報;2012年21期

3 鄭中杰;彭青玉;;2.4米望遠鏡干涉條紋的去除及對測光的影響[J];天文研究與技術(shù);2013年04期

4 尹道先;;透明劈干涉條紋形成的機理及等厚干涉條紋成立的條件——光學(xué)教學(xué)研究之一[J];內(nèi)蒙古大學(xué)學(xué)報(自然科學(xué)版);1980年01期

5 張祖謀;干涉條紋的光電動態(tài)對準[J];光學(xué)技術(shù);1981年05期

6 趙國清;;干涉條紋的分析[J];哈爾濱科學(xué)技術(shù)大學(xué)學(xué)報;1981年01期

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