近地面层湍流大气中光传输到达角起伏实验研究

为研究不同气象条件下近地面层湍流大气对光传输到达角起伏的影响,在校园内一块较平坦草地上开展了光传输实验。 采用半导体激光器作为光源,传输60 m至接收端,使用焦距为1300 mm的望远镜接收后由CCD相机采集光点灰度图片。 根据灰度图片上光点位置计算传输路径上的大气湍流折射结构常数$C_n^2$以及垂直、水平两个方向到达角 (Angle of arrival, AoA)起伏方差的比值。同时测量了传输路径附近的温度、风速等气象数据,计算稳定 度参数Richardson数。结果表明, Richardson数大于临界值0.25时,垂直、水平到达角起伏方差比值均 大于1.0; Richardson 数小于0.25时,垂直、水平到达角起伏方差比值在1.0左右起伏。由此可以看到, 稳定层结条件下,湍流表现为各向异性特征;不稳定层结条件下,湍流表现为各向同性特征。

Experimental Investigation of Angle-of-Arrival Fluctuation of Light Propagating in Near Surface Layer Turbulent Atmosphere

In order to study the influence of turbulent atmosphere in the surface layer on the fluctuation of the angle of arrival(AoA) of light propagation under different meteorological conditions, an optical transmission experiment was carried out on a flat grass in the campus. A semiconductor laser was used as the light source, and the light signal was received by a telescope with focal length of 1300 mm after transmitting 60 m to the receiving location, then a CCD camera was used to shoot grayscale pictures of the light spot. Ratio of the AoA fluctuations in vertical and horizontal directions was calculated based on the position of the light spot on the photo. The atmospheric turbulent refractive structure constant on the transmission path was also calculated. Simultaneously, meteorological parameters near the transmission path, such as temperature and wind speed, were measured so as to calculate the Richardson number as a stability parameter. The results showed that when the Richardson number is greater than 0.25, the ratio of vertical and horizontal AoA variances is greater than 1.0; when the Richardson number is less than 0.25, the ratio of vertical and horizontal AoA variances fluctuates around 1.0. Thus, it can be seen that atmospheric turbulence is anisotropic under stable stratification conditions and isotropic under unstable stratification conditions.