利用闪烁和漂移效应测量大气折射率结构常数的对比分析

Comparison of refractive index structure constants of atmospheric turbulence deduced from scintillation and beam wander effects

在近海面大气边界层中进行了1 km路径的水平光传输实验,结果表明:利用闪烁和漂移效应推导的大气折射率结构常数之间存在着较大的差异。定量的理论分析揭示了两者不一致的原因在于:闪烁效应主要对路径中部的小尺度湍涡敏感,漂移效应则对发射端附近的大尺度湍涡敏感;随着内尺度变大,漂移效应测量的折射率结构常数将大于闪烁效应测量的折射率结构常数,当内尺度达到20 mm时,前者的测量结果是后者的3倍;当外尺度变小时,漂移效应的测量结果小于闪烁效应的测量结果,当外尺度仅为1 m时,前者的测量结果为后者的1/2;大气折射率3维功率谱的幂律的变化对测量结果的影响非常大,当幂律大于-11/3时,闪烁效应测量的折射率结构常数大于漂移效应测量的折射率结构常数,最大差异接近于25倍,当幂律小于-11/3时,漂移效应的测量结果大于闪烁效应的测量结果,两者的差异甚至可达两个量级。

Scintillation effect of divergent laser beam and beam wander effect of a focused laser beam were experimentally used to deduce the refractive index structure constant in atmospheric boundary layer over 1 km path above sea level. Different measurement results of two methods are observed. Theoretical analyses reveal that the reasons for the difference between these two methods as follows： （1）Scintillation is most sensitive to small scale eddies in the centre of the path, however, for beam wander the most sensitive eddies are large scaled and near the transmitter; （2）With the increase of the inner scale from 0 to 20 mm, values of the refractive index structure constant deduced from beam wander effect are larger than that from scintillation. The biggest difference is 3 times when the inner scale is 20 mm; （3）When the outer scale decreases from 20 m to 1 m, the values deduced from beam wander effect is smaller than that from scintillation. The former is only 50% of the latter when the outer scale is 1 m; （4）The deviation of the power law of the three dimensional spectrum of refractive index fluctuations from -11/3 in the inertia region can also cause dramatic difference between scintillation and beam wander effects. When the power law is larger than -11/3, the values deduced from scintillation effect is larger than that from beam wander. The biggest difference may approach 25 times. When the power law is smaller than -11/3, the values of beam wander effect can be tens of times larger than that of scintillation effect.