Study On The Method Of Spot Location Under Atmospheric Turbulence

Free space optical communication is regarded as an effective technique to establish high-speed communication in space.Compared with microwave communication,free space optical communication has the advantages of large communication capacity,high transmission rate,good confidentiality and low power consumptiom,etc.Thus it has aroused widespread concern in countries all over the world.In satellite-to-ground laser communication link,the laser beam propagates through atmosphere within a fairly long distance.and there is always a turbulent effect in the atmosphere,which will cause drift,expansion and fluctuation of the light beam passing through it,leading to the receiving end.Consequently,the spot detected at the receiving end have different degrees of distortion.The traditional spot positioning method has higher positioning accuracy for the spot with good symmetry and uniform distribution,but the accuracy of the traditional positioning method will decrease to some extent as the spot distortion increases.Although the current adaptive optics technology can detect and correct the wavefront phase distortion caused by atmospheric turbulence in real time,the application is still limited due to system design,computer processing capability and data measurement error.Therefore,it is necessary to study the method of spot location suitable for atmospheric turbulence.In this paper,the influence of atmospheric turbulence on the centroid and centroid position of the spot is analyzed.The Zernike polynomial method is used to generate the atmospheric phase screen and simulate the spot affected by turbulence to analyze the distribution and characteristics of the light intensity that may occur under the influence of turbulence.According to the influence of turbulence on the spot distribution,a method for locating the centroid centroid based on the degree of spot distortion is proposed and verified.On the basis of this,using BP neural network to deal with the complex problems of internal mechanism,a method based on BP neural network is proposed,which is based on the characteristic data of the spot,such as centroid,centroid,peak and number of peaks.As an input value to the neural network,the spot feature is weighted by training the model.Atmospheric field experiments were carried out.A large number of spot images affected by turbulence were collected through 11.16 km urban horizontal links in different weather and different time periods,and the spot characteristics with different degrees of distortion were extracted,and the proposed BP neural network-based The spot location algorithm was verified.The verification results show that the proposed algorithm can effectively improve the positioning accuracy of the distortion spot under the influence of atmospheric turbulence.