湍流大气中光波闪烁的圆环孔径平均因子

利用弱起伏条件下球面波在大气湍流中传输的光强起伏(闪烁)理论和圆环孔径滤波函数,获得了圆环孔径平均因子的精确表达式。将圆环孔径平均因子关于一个无量纲参量(孔径半径与菲涅耳尺度的比值)拟合成2阶多项式,再找出多项式系数与孔径内外径之比的函数关系,获得了圆环孔径平均因子关于该参量和孔径内外径之比的函数关系式。通过误差分析确定了拟合关系式的适用范围,在此范围内,拟合式与精确式的相对误差小于25%。分别用Tatarskii谱和修正Hill谱分析了湍流内尺度对圆环孔径平均因子的影响,结果显示:在其他条件不变的情况下,内尺度越大,孔径平均效应相对越小。

Annular-Aperture Averaging Factor of Optical Scintillations in Turbulent Atmosphere

Based on the theory for the irradiance fluctuations(scintillation) of the spherical wave propagating in the turbulent atmosphere and the annular-aperture filtering function,the expression of annular-aperture averaging factor was obtained.The annular-aperture averaging factor was fitted into a second-order polynomial about a dimensionless parameter,i.e.the ratio of the aperture radius to the Fresnel size.After establishing the relationship between the polynomial coefficients and the ratio of the inner to outer diameter of the aperture,the annular aperture averaging factor is expressed approximately as a function of this dimensionless parameter and the ratio of the inner to outer diameter of the aperture.The valid range and accuracy of the fitted approximation were evaluated by error analysis.The effect of the turbulent inner scale on the annular-aperture averaging factor was also analyzed by using Tatarskii spectrum and modified Hill spectrum.The results reveal that,when other conditions keep invariable,the larger the inner scale is,the weaker the averaging effect of the annular aperture is.