| With the development of laser and photoelectric detection technology,blue-green laser marine detection technology has received great development.The research on underwater target detection with blue-green laser has important academic significance and application value.At present,the relevant theoretical models of this research are relatively simple,such as taking seawater as a homogeneous medium and regarding the target surface as an ideal Lambert surface.Therefore,the simulation of laser cross-medium transmission and detection for the fluctuation of sea surface in the natural environment,vertical inhomogeneous distribution of seawater and random roughness of the target surface needs further studied.In this work,the performance of blue-green laser cross-medium transmission and detection is studied using Monte Carlo method combined with the actual marine environment and target characteristic model.This dissertation firstly analyzes the absorption and scattering of light waves by pure water,dissolved organic matter,suspended particles and inorganic salts in seawater,which belong to the inherent optical properties of seawater.Based on the attenuation model of each component of seawater,the vertical seawater stratification model is established by using the measured data of temperature,salinity and chlorophyll concentration in the vertical direction of seawater provided by the Array for Real-time Geostrophic Oceanography(Argo),which provides an optical characteristic model for the study of laser transmission in actual seawater.Secondly,a three-dimensional rough sea surface model is established by using the linear superposition method of equal division frequency,and the cross-medium transmission process of blue-green laser in the atmosphere,air-sea interface and seawater channel is simulated based on Monte Carlo method.Moreover,the effects of wind speed of sea surface,underwater transmission distance and seawater quality on laser cross-medium transmission are analyzed.The results show that the increase of wind speed of sea surface,transmission distance and seawater turbidity will not only increase the energy attenuation,but also change the spot shape and energy distribution of the receiving plane.In this paper,the vertical layered seawater model is used to simulate the underwater laser transmission,and it is analyzed that the attenuation of the vertical layered seawater channel will change non-uniformly with the change of depth.The paper also simulates and analyzes the influence of the transceiver system on the laser transmission.The results show that the change of the divergence angle of the light source will change the time delay and broadening;the change of the emission angle will obviously change the shape and energy distribution of the light spot after transmission;In medium transmission,the increase of the receiving aperture and the field of view will cause serious time broadening.Finally,different from the commonly used ideal Lambertian target surface scattering model,this paper adopts the linear filtering method to establish the underwater random rough surface target model based on the actual rough surface characteristic parameters.The Monte Carlo method combined with the rough surface target model is used to simulate the influence of different parameters in seawater on the echo signal.It is analyzed that the changes of parameters such as sea surface wind speed,seawater quality and target depth will have a greater impact on the echo signal.The paper analyzes the influence of the transceiver system on the target detection echo signal.The results show that the changes of the transmitting angle,the receiving aperture and the field of view angle will have a greater impact on the received echo signal strength;the change of the divergence angle will hardly affect the received energy.The conclusions of this work provide a theoretical reference for the field measurement experiment of blue-green laser cross-medium detection of underwater rough surface targets in natural seawater environment. |
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