摘要
全日面太阳光球像和色球像是监测太阳活动的主要数据,对望远镜观测的原始图像进行平场改正是数据处理过程中的基础工作.本文尝试利用毛玻璃测量全日面太阳光球和色球像的平场,通过理论模拟和实地测量验证了该方法的有效性.首先,模拟计算了太阳经毛玻璃扩散后在观测视场内形成的面光源的均匀性,其均匀度为99%,可以用来测量平场.其次,在全日面太阳光球和色球望远镜上的实验结果表明,本方法获得的平场像能够改正原始观测像中高频的脏点和光路不均匀性,因平场观测和常规观测图像中杂散光影响不同,导致平场改正像存在低频失真,但可通过理论临边昏暗图像对平场改正像进行低频信息修正.修正后的平场改正像与理论临边昏暗像相关系数达到0.99以上.最后,以HMI发布的光球像和GONG发布的色球像作为参考像,选取活动区所在小视场和宁静区大视场,分别与利用本方法实验改正后的光球像和色球像进行了结构相似度等方面的量化对比.对比结果表明,改正像的各项指标均优于原始像.本文提出的平场测量和改正方法简便易行,且容易实现自动化测量,为全日面太阳望远镜的平场测量和改正提供了新方法.
Full-disk solar chromosphere and photosphere images are mainly used for monitoring solar activities. Flat-field correction of observation image is a basic work during data processing. In history, it is difficult to obtain uniform area light whose intensity is similar as sun. So flat-field measurement and correction of full-disk solar image usually depend on moving images and mathematical calculation. In order to overcome some disadvantages of traditional methods, such as large calculating quantity, complicated algorithms and difficult to realize automation, we research and design a new flat-field correction method based on ground glass. In this text, sunlight diffused by ground glass in field of view is used as uniform area light for flat-field measuring. We simulated the area light that sun diffused by ground glass, calculated the uniformity of area light in field of view. The uniformity of area light is more than 99%, so it can be used as uniform area light for flat-field measurement directly. We designed flat-field measurement device and formulate steps and methods for flat-field correction. After numerical stimulation and calculation, experiments carried out on solar chromospheres telescope and photosphere telescope separately. The result shows that the flat field obtained in this text could correct high-frequency information such as spots and non-uniformity of light path. Subjected to telescopes limited ability to eliminate stray light, flat-field measurement and correction also causes low-frequency information anamorphous because the angle of diffused light is much larger than normal observation. In order to amend low-frequency information distortion, we use multi-scale morphology filtering and median filtering to extract the low-frequency image from flat-field corrected image. Then the extracted low-frequency image is amended on the basis of theoretical limb darkening image. After flat-field correction and amendment, the correlation coefficient between corrected image and theoretical image is more than 0.9
出处
《科学通报》
EI
CAS
CSCD
北大核心
2017年第26期3057-3066,共10页
Chinese Science Bulletin
基金
国家自然科学基金(11503063
11178005
11427901)资助
关键词
毛玻璃
太阳望远镜
平场测量
图像处理
空间环境
ground glass
solar telescope
flat-field measurement
image analysis
space environment
