扩展目标夏克-哈特曼波前传感器子图像之间偏移量的计算是影响波前传感精度的关键,通常采用相关算法来实现,并通过抛物线插值等方法来达到亚像元精度。子图像相对偏移量的计算也可以采用计算相关函数质心的方法来实现,其主要步骤是先计算子图像间的相关函数,在此基础上计算相关函数的质心,达到亚像元精度。通过仿真研究表明这种算法的精度与进行相关运算时的图像大小、计算质心时的相关函数窗口大小以及相关函数阈值的设定有关;同时,图像的信噪比也会影响算法的精度。研究表明,图像的信噪比小于1时,质心算法的计算误差相对较大;当图像的信噪比高于2时,相关函数质心算法的误差大约是抛物线插值法误差的一半。实验结果与仿真结果也基本吻合。

The calculation of the shifts between sub-images in extended scene Shack-Hartmann wavefront sensor is one of the key factors affecting the accuracy of wavefront sensing, which is commonly achieved by correlation algorithm and it can attain sub-pixel precision through methods such as parabolic interpolation algorithm. The calculation can also be achieved by using the centroid of the correlation function. The main step is first calculating the correlation function between two sub-images and then calculating the centroid of the correlation function, which achieves sub-pixel precision. Based on simulation, the measurement accuracy of this method is related to the size of the sub-image, the window size of the correlation function in the calculation of the centroid and threshold of the correlation function. Besides, the signal-to-noise ratio of the image also effects the accuracy of the calculation. Studies show that, when the signal-to-noise ratio of the image is less than 1, the error of the centroid algorithm is relatively large. When the signal-to-noise ratio of the image is larger than 2, the error of the centroid-of-correlation-function approach is only half of that of the parabolic interpolation. The experimental results are in good agreement with the simulation results.