基于系列斑点图像的视宁度估算精度方法研究

Seeing Estimation Accuracy Study Based on a Sequence of Speckle Images

半高宽法和像运动法是估算大气视宁度的常用方法,两种方法的估算精度都受到望远镜跟踪误差、风或者机械振动等因素的影响,提高视宁度估算精度在高分辨成像、选址、台站视宁度监测等方面有重要意义。对于半高宽法,用二维高斯函数拟合长曝光点源单星星像并选取合适方向的半高宽估算视宁度,可以有效改善跟踪误差、风或者机械振动等因素的影响。对于像运动法,用主成分分析法找到一系列斑点图重心位置在合适方向上投影的方差,以此估算视宁度,与谱比法对照可以发现,两种方法均能有效改善跟踪误差、风或者机械振动等因素的影响。

FWHM and image motion are two frequently used methods in the field of astronomy.However,estimation accuracy of these two methods will be affected by tracking error,wind and mechanical vibration.Raising its accuracy plays a rather important role in the area of high-resolution imaging,site selection and seeing monitoring of observatories,etc.For FWHM method,we fit the long exposure image with a two-dimensional gaussian function and choose an appropriate direction to measure its FWHM by which we estimate the seeing parameter.A comparison with spectral ratio method shows a great improvement of our approach against tracking error,wind and mechanical vibration.For image motion method,we employ principle component analysis to project center of gravity coordinates of a sequence of tracking error affected speckle images onto a proper direction on which we find its variance.We further utilize the variance to estimate the seeing parameter.A comparison with spectral ratio method also denotes a considerable improvement of our approach against tracking error,wind and mechanical vibration.