双孔差分闪烁法测量大气湍流的理论与实验研究∗

摘要

根据cross-path理论，推导出弱起伏条件下差分孔径光强起伏结构函数的精确表达式，以此为依据，从理论上提出测量大气湍流强度的双孔差分闪烁法.在Kolmogorov湍流谱条件下，分析了信标光直径和信标光高度对该方法中路径权重函数的影响.在近地面开展了2 km路径的水平光单程传输实验，将双孔差分闪烁法和单孔闪烁法的测量结果进行了对比.实验结果表明：在不同的天气条件和大气湍流状况下，两种方法测量的折射率结构常数具有高度的一致性；通过对折射率结构常数积分得到的球面波大气相干长度进行相关性分析，发现两者的线性相关系数达0.96；由此验证了双孔差分闪烁法的可行性和有效性.该方法能够分离出主动信标双程传输的后向闪烁信息，为主动信标准确探测大气湍流提供了一种新方法.%We report the basic theory and first horizontal results of a method called two-aperture differential scintillation method which is aimed at monitoring the vertical profile of atmospheric optical turbulence strength. The method is based on irradiance fluctuation of active light source, but can extract the optical turbulence information in the single-passage path. In this paper, the theoretical principle of two-aperture differential scintillation method is derived in detail. A concise expression is proposed for irradiance fluctuation structure function with differential aperture in the Rytov approximation under a weak fluctuation regime based on the cross-path theory. The mathematic relationship between irradiance fluctuation structure function and atmospheric optical turbulence strength is then developed. The effects of beacon aperture and beacon altitude on path weighting function of this method are analyzed for Kolmogorov turbulence. In order to test the validity of the new method, the experiments are conducted to compare the two-aperture differential scintillation method and single-aperture scintillation method in atmospheric boundary layer over 2 km horizontal single-passage path. In this arrangement, we employ a differential image motion monitor system to measure differential scintillation. Simultaneously, a large aperture scintillation instrument is placed 5 m away at the same altitude to measure the single-aperture scintillation. It is shown that the results of atmospheric refractive index structure constant deduced from the two methods are in good agreement. The measurements of atmospheric coherence length for spherical wave corresponding to the two methods indicate a linear correction factor (R2) of 0.96, in a slope of 0.98 with an offset of −0.09 cm. Feasibility and effectiveness of two-aperture differential scintillation method are thus verified experimentally. The novel method can separate single-passage scintillation information of active beacon double-passage propagation, thereby providing an accurate technique for measuring the atmospheric turbulence of active beacon.