抚仙湖太阳观测和研究基地知识库

太阳强热辐射导致太阳望远镜光机系统热形变，引发较明显的时变焦点位置漂移。离焦像差影响高分辨观测，降低观测图像的空间分辨率，因此需要探测并补偿望远镜的离焦像差。由于大气湍流的影响，一般的基于图像处理的焦点探测方法不能有效地运用于地基太阳望远镜。而天文望远镜常用的基于Shack-Hartman 波前探测的方法，在观测太阳边缘和低对比度的太阳米粒结构时无法工作。本文提出了一种基于图像能谱分析的焦点探测方法，该方法以图像能谱比的低频分量的平均值作为焦点探测评价函数，该方法能够消除目标信息的影响和平滑大气湍流的影响。实验证明，该方法的探测精度和探测时间分辨率能满足地基太阳望远镜不同观测目标的高分辨观测的需要。

Intense solar radiation leads to thermal deformation of the solar telescope opto-mechanical system, triggering obvious time-varying focus shifts. Defocus aberration has an adverse effect on high-resolution observation and reduces the image spatial resolution. Therefore, the defocus aberration is necessary to be detected and compensated. Considering the effects of atmospheric turbulence, the focus detecting method based on Shack-Hartman wavefront detection which commonly used in astronomical telescopes is invalid at observing the solar limb and the low contrast solar granulation. The focus detecting method based on image power spectrum analysis is provided. This method used the averate value of the low-frequency components of the image spectrum ratio as the cost function for focus detection, which can effectively eliminate the impact of object structure and atmospheric turbulence. Experimental results show that the detecting accuracy and frequency of this method can meet the requirement of high-resolution observations for different objects on ground-based solar telescope.