CCD噪声对星敏感器星点定位精度的影响

星点测量精度是表征星敏感器精度的一个重要指标，影响该精度的主要因素有：光学系统误差、图像传感器的噪声、电路噪声及软件算法等。图像传感器的噪声对星点定位精度的影响是不容忽视的，但很少对此进行研究。针对某给定参数的星敏感器，对TH7890M CCD图像传感器的各项噪声进行了定量计算；基于亚像素细分质心算法，针对各噪声的分布特点及规律，分别推导出各自的均方根误差，综合各项误差得到CCD噪声的星点定位精度模型。计算结果表明TH7890M CCD的主要噪声有读出噪声、光子散粒噪声和光响应不均匀性引起的随机噪声；影响星敏感器星点定位精度的主要噪声是读出噪声和光子散粒噪声；对6等星进行星点位置的估计，CCD噪声达到了1/40像素的精度水平。

CCD noise effects on position accuracy of star sensor

Measurement accuracy of star point is an important character of star sensor accuracy, and it is restricted by optical system error, CCD image sensor noise, circuit noise, arithmetic, etc. Image sensor noise is not negligible, but it is studied rarely. So noise of TH7890M CCD chip, which was used for developing star sensor, was calculated quantitatively. Then based on the subpixel centroid arithmetic, RMS error of different noises was deduced respectively according to respective different noises distribution regular. At last, CCD centroid position accuracy model was received by synthesis. The results show that TH7890M CCD chip has three main noises, i.e. readout noise, photon shot noise and random noise caused by photoresponse nonuniformity, and the preceding two are the main factors which affect star sensor accuracy. For star position estimation, CCD noises can achieve accuracy level of 1/40 pixel for a 6 magnitude stars.