数字天顶摄像仪中CCD星像亚像素定位的改进二维矩方法

Improved Two-dimensional Moment Method of Positioning Sub-pixel of CCD Star Image from Digital Zenith Camera

在利用数字天顶摄像仪通过天文测量确定天文垂线偏差的工作中,要求对CCD数字图像中星像中心进行亚像素定位。利用MATLAB实现对FITS格式CCD天文图像的正确读取,利用矩形模板实现不同亮度星像的自动搜索。在已有亚像素定位的修正矩方法基础上,提出利用迭代法寻求合适门限对二维修正矩方法进行改进。利用MATLAB实现对实测CCD星像数据的处理与分析,探讨门限的取值对不同星等恒星定位精度的影响,给出门限的最佳取值。通过与已有修正矩算法处理结果比较分析,在修正矩方法计算基础上改进计算区域后再用迭代法计算,暗星定位精度可达0.1～0.15像素。

Precise star-centroid determination of digital star image screened with CCD is important to estimate the precise astronomical location of observing station in the surveying of vertical deflection based on GPS and CCD techniques with the astro-geodetic method. The sub-pixel center of CCD star image should precisely be positioned to improve the precision of station astronomical latitude and longitude with the digital zenith camera. A program is developed with MATLAB to read CCD image in FITS format. Star images with different magnitudes can automatically be found with an adaptive rectangle template model. Based on the analysis of CCDstar image, the two-dimensional moment method is improved to process reaICCDstarimages. The threshold value selected in the moment method in common use can seriously affect the positioning precisions of star images with different brightness. So an iterative method to calculate the optimal threshold is put forward. Compared with the two-dimensional modified moment method, the improved two-dimensional moment method is of more efficiency, precision and reliability. More precise positioning results for dark stars are acquired with the improved method and the positioning precision for dark stars is up to 0.1-0.15 pixel.