大气相干长度的稳定测量

Steady measurement of atmospheric turbulence coherence length

采用传统的一对差分星点像运动法(DIMM)测量大气相干长度r0时,受统计星点对数的限制很难得到稳定的r0数值。因此,本文提出将对波面上一对星点像运动的统计增加为对正方形分布的十二对星点像运动的统计,并利用Shack-Hartmann波前探测器采集的光点阵列实现了这种统计。畸变波面上十二对点的差分运动统计方法从空间角度上增加了大气相干长度r0采样的统计数量,从空间群的概念来说增加了中心对称统计,因此大幅降低了统计时间。实验显示:仅使用300ms采样300幅畸变波面即可完成对大气相干长度r0的统计,得出稳定而准确的r0值,而波动只有±3%。该方法解决了长期以来大气相干长度r0的统计量不确定、测定误差无法分析的问题,有助于提高地基望远镜自适应光学系统成像的精度。

When atmospheric turbulence coherence length r0 is measured by traditional Differential Im- age Motion Monitor（DIMM） method, it is difficult to obtain a stable r0 value due to limitation of light spot pairs. Therefore, this paper proposes a statistical method to increase the statistical number of light spot pairs from one on a wavefront to twelve aligned in a square, and completes the statistics on a SHWFS light spot array captured by the Shack-Hartmann wavefront detector. The method spatially increases the statistical number of samplings and the spatial symmetry of r0 measurement, so it de- creases the statistical time greatly. The experiments show that only three hundred of wavefront samples gotten in 300 ms are enough to obtain the r0 with a variation less than 3 %. The presented method solves the large error problem in the traditional r0 measurement for long time, and has contributed to the improvement of imaging accuracy of adaptive optical systems for ground-based telescopes.