Influence Of Water Non-uniform Characteristics On The Underwater Wireless Optical Positioning And Pointing Performances

In the process of marine resource development,the demand for underwater posi-tioning is increasing,such as the layout of underwater network nodes,the recovery and docking of underwater autonomous vehicles,path planning and so on.For some new underwater application scenarios which require high positioning accuracy,the optical wireless positioning and pointing system is a better supplementary scheme.However,the marine environment is complex.The scattering and attenuation of the sea water,refractive index changes,water turbulence,and bubbles in the ocean pose challenges for the optical wireless positioning and pointing system.This work mainly studies the influence of the non-uniform characteristics of the seawater on the performance of the underwater optical wireless positioning and pointing system and explores its compensation scheme.The change of the refractive index of the seawater causes ray bending,and the turbulence of the seawater mainly causes the distortion and diffusion of the light beam near the optical axis.Both of these factors will degrade the performance of the optical wireless positioning and pointing system.This work develops the model of the refractive index of seawater with depth ac-cording to the actual ocean data set,which is the basis for subsequent research.Regard-ing the influence of underwater turbulence,this work set up an underwater turbulence simulation experiment platform to explore the impact of different types and different intensities of turbulence on the imaging spot,and fitted the underwater turbulence spot center distribution model.Regarding the underwater wireless optical pointing system,this work derives the analytical solution of the ray-bending formula to analyze the influence of the change of refractive index on the angle estimation.Compared with the commonly used nu-merical methods,the results obtained by the formula method are more accurate.At the same time,based on the principle of underwater turbulence,this work optimizes the single-frame spot search algorithm in a turbulent environment,and proposes the Fourier Phase algorithm to improve the accuracy of spot center estimation.Compared with the traditional algorithm,the Fourier Phase method performs well in the case of strong turbulence,which is supported by the experiment.In the three-dimensional space,the positioning deviation caused by the ray-bending is mainly concentrated in the depth direction,while the horizontal direction positioning deviation is small.The formula calculation shows that when the distance between the transmitter and receiver is 300m,the estimated position error of the target object point caused by the light bending in the seawater due to the change of refractive index can reach about 30cm.In a turbulent environment,the camera spacing of the binocular positioning system should not be too small,otherwise the positioning perfor-mance will decline rapidly.