Research On Transmission Characteristics Of Cross-medium Laser

With the advancement of the globalization of network coverage,the cross-medium laser communication between underwater and aerial platforms has become one of the hot research fields in recent years.In this type of communication,the channel is composed of seawater,sea/air interface and atmosphere.Because of its complex composition,there are many factors affecting the beam propagation.So far,there is no recognized cross-medium channel model.Therefore,it is still a very challenging task to ensure the stability and reliability of cross medium laser communication.The existing blue-green laser cross-medium communication research has the following problems:(1)In the vertical link underwater optical communication,sea water is set as a uniform medium;(2)In the study of atmospheric channel,there is no turbulence profile model that conforms to the Marine environment;(3)The lack of a phase screen distribution method that conforms to the description of turbulent fluctuations in the marine environment.To solve the above problems,the transmission characteristics of the cross-medium laser uplink channel are studied in this paper,and its structure is as follows:Firstly,the effects of seawater composition on light absorption and scattering are analyzed.Seawater is considered to be an inhomogeneous medium,based on the measured data of chlorophyll a concentration in vertical seawater from Argo buoys,and the relationship between the concentration of chlorophyll a and the diffusion attenuation coefficient K _d(490),the vertical distribution of the seawater attenuation coefficient is given.The distribution is used to layer the seawater to establish a more accurate underwater wireless optical communication channel model.Then,using the P-M spectrum and the direction function suggested by ITTC,the bilinear superposition method is used to model the three-dimensional random waves.Analytical geometry and vector algebra are also used to derive and analyze the refraction effect caused by the light spots passing through the waves.Finally,point out the turbulence profile model suitable for the marine environment.According to the Non-Kolmogorov turbulence spectrum theory,the channel model of the beam propagating in the turbulent atmosphere is modeled,and a phase screen distribution set by a hybrid method is proposed.This paper proposes that the phase screen distribution method is more suitable for atmospheric turbulence fluctuation in Marine environment than the phase screen method with equal Rytov exponent interval.In the completed cross-medium channel research work,this paper analyzes the media in each channel in detail.Based on the measured data of the chlorophyll a concentration in the vertical seawater of the Argo buoy,the vertical distribution of the seawater attenuation coefficient is given,so as to take a stratified analysis of non-uniformly distributed seawater;a turbulence profile model suitable for marine environments and the best phase screen distribution method are also proposed,which makes the cross-medium channel model more consistent with the actual situation.Therefore,this article provides a reference to build a complete and practical communication system simulation platform,and use this simulation platform to replace real experimental measurements in complex communication environments and harsh conditions,thereby saving a lot of manpower and material resources.