获取非等晕幸运短曝光图像的概率研究

Probability of getting anisoplanatic lucky short-exposure images

通过湍流大气进行短曝光成像,存在一定的概率能够获得接近系统衍射极限分辨率的图像,瞬间的波前畸变可以忽略不计。通过设计不同望远镜口径的短曝光成像观测实验,应用基于灰度梯度统计的像质评价函数对序列短曝光图像进行了像质评价,并运用归一化处理来研究非等晕条件下获取幸运短曝光图像的概率。处理结果验证了"幸运图像"的获取概率随着口径的增加而逐渐下降,与Fried得出的概率公式中概率随着口径和大气相干长度的比值的增大而呈指数级下降的模式基本吻合,且通过图像分块的进一步分析表明,在非等晕条件下获得"幸运区域"的概率比等晕条件下获得"幸运图像"的概率大。

In short-exposure imaging through atmospheric turbulence, there is some probability that the image will be nearly diffraction limited because the instantaneous wave-front distortion over the aperture is negligible. Observation experiments of short-exposure imaging with different telescope apertures were designed firstly, and then the image quality of sequence short-exposure images were evaluated based on statistics of gray gradient. At last, the probability of getting an anisoplanatic lucky short-exposure image was studied through normalization of image quality values. The experimental results indicate that the probability of getting a lucky image will decrease with the increase of aperture area, which is basically consistent with the model that the probability is exponentially declined with the ratio of aperture diameter and atmosphere coherence length, as defined by Fried. The further analysis and comparison show that the probability of having a lucky region within a single short-exposure frame under anisoplanatic conditions should be higher than the corresponding probability of getting a lucky frame under isoplanatic conditions.