星点质心亚像元定位的高精度误差补偿法

在CCD星敏感器设计过程中,星点坐标的提取精度不仅影响星图识别的正确性,也直接影响星敏感器的最终姿态输出精度。本文通过分析传统质心法亚像元提取算法误差模型,证明该模型存在系统误差和随机误差。针对系统误差,提出了用最小二乘拟合法来估计质心位置和系统误差大小的对应关系,利用这个关系对系统误差进行补偿;针对随机误差,提出用边缘阈值法和星图整体相消法来消除。本文还分析了CCD成像数学模型,星光成像的能量分布近似服从二维高斯分布,星点高斯分布弥散半径不同,用于误差补偿的曲线方程也不一样,根据不同的高斯弥散半径,设计了误差补偿模板,用于补偿质心法的系统误差。实验表明,采用误差补偿模板,可以将质心法精度从1/20pixel提高到1/200pix-el,满足了星敏感器高精度星点质心提取的要求。

High accuracy error compensation algorithm for star image sub-pixel subdivision location

The precision of centroid location for star images is an important factor, which affects the correction of star identification and the precision of star attitude determination. In this paper, the error model using the traditional Center of Mass (COM) is analyzed and it is shown that there are systematic errors and random errors in the COM. For the systematic errors, this paper firstly analyzes the relation between the systematic errors and the calculated centroid position by a simulation, and then adopts the least square curve fitting algorithm to estimate parameters of bivariate polynomial and to compensate systematic errors. For random errors, it presents an edge threshoold method and a star image elimination method to remove errors. Furthermore, the CCD imaging model is analyzed and a Bivariate Polynomial Compensation Template (BPCT) is proposed. As the star intensity distribution is close to the Gaussian point spread function model and the BPCT is related to the dispersion size of star intensity distribution, the different BPCTs are calculated to compensate the systematic error of COM according to different sizes of star dispersion. The simulation results show that by using the BPCT, the accuracy of the star position can be enhanced from 1/20 pixel to 1/200 pixel, which meets the requrirements of star trackers for the high accuracy centroid location.