Research On Light Transmission Characteristics Of Water Mist Media Based On Monte Carlo Method

With the development of detection and imaging technology in optical wavelength band,studies of light transmission characteristics in the atmosphere has attracted much attention in many application fields such as target detection and identification,optical remote sensing imaging,and opto-electronic countermeasures.Light transmission in the atmosphere can be interfered by aerosol particles,which not only cause energy attenuation along the transmission path,but also reduce the imaging quality and thus affect the accuracy of target identification in some fields for imaging and target identification purposes.Fog is a kind of aerosol which occurs in the near ground area frequently,investigation on light transmission characteristics in fog is of great scientific and practical value for optical communication,weather detection and target identification.This paper inspects the development status and trend of the research on the optical transmission properties of fog media as well as the radiation transfer calculation method at home and abroad,describes the parameters which characterize the optical properties of discrete random media and the related theory of radiation transfer,analyzes the optical properties of fog media,and establishes a Monte Carlo model based on dynamic particle parameter selection(DPPS-MC),which can be used to simulate the transmission of light in fog media.At the same time,aiming at the light transmission characteristics of fog media in complex scenes,factors which affect the differences in optical transmission characteristics of fog media in complex scenes are analyzed by constructing complex scenes and establishing a radiative transfer calculation model.The main work of the thesis is as follows:1.Based on the light transission theory in discrete random media,the physical process of light propagating in fog media is analyzed,and the possible problems of using Monte Carlo method for the calculation of light transmission characteristics in fog media are summarized.By establishing a reasonable collision probability model and dynamically selecting the optical parameters of particles in media based on the collision probability,a Monte Carlo model based on dynamic particle parameter selection(DPPS-MC)is proposed,which can simulate the light transmission process in fog media more realistically.2.The common fog droplet distribution models are summarized,the differences between different models are compared,and the refractive indices of fog droplet particles are calculated for wide wavelength band.Based on fog droplet distribution models,the optical parameters of fog droplet particles are calculated using Mie theory,transport approximation theory.The influence of optical parameters of the media on the simulated results and computational time of the Monte Carlo method is analyzed.A method which can calculate the transmission attenuation of light in fog fastly is proposed by combining the transport approximation theory and DPPS-MC,and the reliability of the Monte Carlo method is analyzed.The results show that the DPPS-MC based on the transport approximation theory can effectively shorten the computational time and improve the computational efficiency when calculating the transmission attenuation in fog medium under long-distance and large incident angle conditions.3.Aiming at the optical transmission characteristics of fog medium in complex scenes,the complex ocean scenes is constructed by modeling the sea fog and sea surface.In the process of modeling the sea surface,the influence of wind speed on waves is considered,the advantages and disadvantages of several common wave power spectrum are compared,by modifying the wave power spectrum and combining with the linear filtering method,the geometric model of the sea surface is generated.The sea surface modeling method based on wave power spectrum correction can obtain more accurate sea surface slope distribution with less sampling interval,which effectively improves the computational efficiency.The light transmission process in complex ocean scenes covered by sea fog is analyzed,and a radiative transfer calculation model which is suitable for complex ocean scenes is established,the reliability of simulation results of Monte Carlo method and the light transmission characteristics of wind-driven rough sea surface are analyzed.On this basis,the established model is used to simulate the light transmission process in complex ocean scenes,and the characteristics of the bidirectional reflectance distribution of sea fog with different fog layer thickness,water content,incident angle and wind speed are studied,and the coupling influence mechanism of environmental factors on the light transmission characteristics of fog media in complex maritime scenes is revealed.Analyzing the optical transmission characteristics of fog media can provide theoretical and data basis for optical communication,remote sensing detection and target identification and detection under foggy weather,which is of great significance to promote the technical development and application in related fields.