Experimental Study Of Influences Of Anisotropic Turbulence On Light Propagation At The Surface Layer

Most existing turbulence theory and the theory of effects of turbulence on light propagation are based on isotropic turbulence assumptions.However,actual turbulent atmosphere often exhibits anisotropic characteristics.In this paper,an anisotropic model of turbulence is introduced.The effect of anisotropic turbulence on the intensity and angle of arrival of light propagation is analyzed by numerical simulations.Then an external field experiment of light propagation is carried out in the surface layer,the following results are obtained:According to the characteristics of atmospheric turbulence in the surface layer,a three-dimensional spectral density ellipsoid model which extends in the horizontal plane and compresses in the vertical direction is used to describe the anisotropic turbulence.The coefficient that characterize the anisotropy is then introduced into the Von Karman three-dimensional spectrum.Numerical simulations of multiphase light propagation showed that the effects of anisotropic turbulence on the fluctuation of light intensity at the large scale is the same as that under isotropic conditions,but the effects of anisotropic turbulence at the large scale is significantly different from that under isotropic conditions.When changing the anisotropic coefficient,the ratio of the angle-of-arrival fluctuations in the vertical and horizontal directions also changes.There is a clear functional relationship between the two,and this quantitative relationship is given in this paper.Through continuously measuring meteorological elements such as wind speed and temperature for a long time,the daily variation characteristics of atmospheric temperature stratification stability were obtained.At the same time,we measured the ratio of the vertical and horizontal angles of arrival fluctuations and found a regular correspondence between this ratio and the Richardson number:When the Richardson number is positive,the ratio is always greater than 1 and when the Richardson number is negative,this ratio fluctuates around 1.Based on the results of comprehensive numerical simulations and field measurements,it is believed that there is a corresponding relationship between the anisotropic characteristics of atmospheric turbulence and the stability of atmospheric temperature stratification.When the temperature stratification is stable,the turbulent atmosphere exhibits anisotropic characteristics,and when the temperature stratification is unstable,the turbulent atmosphere exhibits isotropic characteristics.This conclusion can be used to guide the measurement of atmospheric turbulence and inversion of turbulent parameters based on the existing isotropic theory.It can also be used to determine whether the near-surface turbulent atmosphere exhibits obvious anisotropy through optical measurement.