抚仙湖太阳观测和研究基地知识库

由于太阳辐射、环境温度等因素,太阳望远镜在一个观测日内往往有较明显的像差变化,而离焦是其中的主要像差。针对抚仙湖1 m太阳望远镜的高分辨成像观测系统,对其离焦像差及变化进行了简要分析,在此基础上模拟分析了离焦像差对图像高分辨统计重建的影响。分析结果表明,离焦像差对高分辨重建图像的相位传递函数影响不大,但对调制传递函数有明显的影响,进而造成像质衰减,应当进行补偿。

The 1m New Vacuum Solar Telescope (NVST) in the Fuxian Solar Observatory (FSO) of the Yunnan Observatories is currently the largest ground-based solar telescope in China.The primary scientific task of the NVST is high-resolution observation of the sun.Images from the ground-based NVST are inevitably blurred by atmospheric turbulences, and some high-resolution statistical reconstruction techniques (such as the speckle interferometry and speckle masking) need to be adopted to remove effects from atmospheric turbulences.However, reconstruction results with the techniques are affected by aberrations of the NVST.Due to solar radiations and environmental temperature variations there are appreciable aberration changes in a day. Changes of defocus aberrations have major contributions to overall aberration changes.In this paper we present analyses of defocus aberrations of the NVST and their temporal variations using the NVST high-resolution imaging system.We subsequently investigate influences of defocus aberrations on high-resolution statistical reconstruction of NVST data.Our preliminary estimation shows that in a typical day of observation the average and maximum variations of defocus aberrations of the NVST are about 1.8λand 1λ, respectively.Our numerical simulations illustrate that defocus aberrations significantly influence the Module Transfer Functions (MTFs) of reconstructed images, but affect little the Phase Transfer Functions (PTFs) of the images.If defocus aberrations are above about 2λspatial resolutions of reconstructed images for the NVST decrease rapidly as defocus aberrations increase.We conclude from these that defocus aberrations should be appropriately compensated to make reconstructed images of the NVST to have sufficient quality.