中文摘要：

对绝对差分算法检测太阳边缘的起伏测量白日视宁度的方法进行了研究，并对绝对差分的结果进行二阶拟合使之可以达到亚像素的检测精度。对可能的影响因素如噪声和像差等进行了分析和数值模拟，算法的精度优于0．1”。模拟结果表明，采用绝对差分算法可以对白日视宁度进行高精度的测量，最后用绝对差分算法对实际数据进行了处理，给出了初步结果。

英文摘要：

A Solar Differential Image Motion Monitor （S-DIMM） is an important instrument to measure the day-time seeing r0. S-DIMMs al：e widely used in solar telescope site testings. An S-DIMM yields the day- time seeing by measuring fluctuations of the images of the solar edge. In this paper, we adopt the Absolute Difference Algorithm for solar-edge detection to measure the day-time seeing, with the second-order fitting used to improve the accuracy on the sub-pixel level. This not only solves problems caused by the small field of view of an S-DIMM, which leads to instability in observations in addition to atmospheric effects, but also helps long and steady observations with an S-DIMM. We also analyze possible factors （such as noise and aberration） influencing the Absolute Difference Algorithm with the aid of numerical simulations. The simulations show that the Absolute Difference Algorithm can be used to undertake high-precision observations, with the accuracy of the algorithm better than 0.1＂. Finally, we apply the algorithm to real measurement of seeing, and present some preliminary results.