湍流大气外尺度对波束地-空传播闪烁影响研究

根据在中度和强湍流大气条件下引入空间频率滤波函数的修正Rytov方法,从理论上给出了地-空斜程路径上从弱到强起伏下包含湍流内、外尺度效应的激光高斯波束闪烁指数模型.该模型在相应的条件下分别可转变为波束波水平视距路径传播的闪烁模型和平面、球面波的闪烁指数模型.应用该模型,分析了湍流内、外尺度对波束波地-空路径传播时闪烁指数的影响.结果表明,在中度起伏条件下,内尺度对闪烁的影响是相当显著的,而外尺度的影响较小;从中到强起伏区,随着湍流强度的增加或传播距离的增加,外尺度影响逐渐的增大;在强起伏区,外尺度的影响已达到与内尺度影响具有同样的程度.因此,对于光波束在较强湍流中传播或在大气中传播路径较长时,对光波束闪烁预测不但要考虑内尺度效应,而且也要考虑外尺度效应.

Scintillation of beam wave propagation along Earth-space paths from outer-scale of turbulent atmosphere

Based on the modificed Rytov method that incorporates spatial frequency filter function under moderate and strong fluctuation conditions, a scintillation index model is proposed for laser Gaussian beam propagation along Earth-space slant paths in turbulent atmosphere. The model includes the effects of the outer-scale in addition to the inner-scale of turbulent atmosphere. Under some conditions, the model can be converted into the scintillation index model for beam wave propagation on horizontal sight paths and also degraded to plane and spherical wave scintillation models, respectively. The effects of the outer-and inner-scale on scintillation index are analyzed, and the results show that the inner-scale effect is remarkable and the outer-scale effect appears small in moderate fluctuation regime. From moderate to strong fluctuation regime, however, the effect of the outer-scale increases with turbulent fluctuation or propagation distance increase. In strong fluctuation regime, the effect of the outer-scale on scintillation index is approximate to the inner-scale effect. Hence, under stronger fluctuation or farther propagation distance conditions, not only the effect of inner-scale, but also the effect of outer-scale on the scintillation index may be taken into account for scintillation prediction of laser beam propagation through turbulent atmosphere.