Research On Fluorescence Characteristics Simulation And Detection Method Of Oil Spill On The Sea Based On LIF

Oil spill is one of the most natural marine disasters,which poses a grievous threat to the marine environment.Generally,oil spills at sea are divided into three weathering stages: non-emulsification,emulsification,and degradation.Among them,the non-emulsification stage includes thick oil film,thin oil film and discontinuous oil film,and the emulsification stage includes water-in-oil,oil-in-water and other types of oil spill pollution.Laser Induced Fluorescence(LIF)has the ability to accurately identify oil species,qualitatively and quantitatively detect the scope of oil spills,oil film thickness,and pollution degree.It is currently the most advanced monitoring tool in the field of marine remote sensing.Nowadays,a complete and scientific detection theory system as well as a comprehensive and mature monitoring methods has not been formed of the different pollution types for oil spills on the sea surface based on LIF detection technology.In the face of serious limitations in the detection and evaluation of thick oil films on the sea surface and the lack of thoroughgoing and scientific detection theories and methods for emulsified oil spills,it is a meaningful assignment to carry out research on the detection methods of thick oil films and emulsified oil spills at sea based on LIF.Yet the research and analysis of the fluorescence characteristics for oil spills is the key and basis for LIF to detect and evaluate different pollution types for oil spills on the sea surface.Therefore,based on LIF detection technology,this paper conducts research on the fluorescence characteristics simulation and detection methods of oil spills on the sea.Firstly,the optical properties of different types for oil spill pollution on the sea surface are comprehensively analyzed.The non-emulsified and emulsified oil spills on the sea surface are subdivided into different types of pollution.Simultaneously,the intrinsic optical parameters such as scattering coefficient,extinction coefficient and fluorescence properties such as fluorescence quantum yield for different pollution types of oil film,water-in-oil and oil-in-water are calculated and analyzed.The optical properties of different types of oil spill pollution on the sea surface discussed in this chapter lay a significant foundation for subsequent researches.Secondly,the fluorescence characteristics of emulsified oil spills on the sea surface are simulated and deliberated.Based on the Monte Carlo method,a fluorescence radiation transfer model for emulsified oil spills on the sea surface is established,and the effectiveness of the model are verified by experiments.On this foundation,the fluorescence radiative transfer model is utilized to simulate and analyze the fluorescence emission direction and emission position distribution characteristics of emulsified oil spill at sea level under different thickness,concentration and other parameters.The dependence of fluorescence characteristics on detection parameters such as detection angle and detection area for coaxial transmit-receive form is discussed.The suitable detection parameters for various emulsified oil spills during LIF detection are summarized.Thirdly,aiming at the problem of evaluating thick oil film,an algorithm for evaluating thick oil film on the sea surface based on fluorescence signals is proposed.The transmission mechanism of photons in oil film media is employed as a basis,the non-coaxial and coaxial detection modes of LIF detection system are involved,and the influence of detection angle under different detection modes are considered.In this way,a functional relationship between the fluorescence signal intensity of oil film and its thickness is established.The mixture of crude oil and white oil serves to the experimental oil.The effectiveness of the evaluation algorithm are verified by collecting the fluorescence spectra of oil films with different thicknesses under different detection modes and detection angles.Then,aiming at the problem of evaluating the concentration of emulsified oil spills on the sea surface,an inversion model of emulsified oil spill concentration based on fluorescence flux is proposed.In view of the laser flux,the fluorescence flux is expanded.The average path-length and forward-scattering ratio of luminous flux are introduced.Concurrently,the laws of absorption and scattering of photons as they transport in the emulsified oil spill medium and at the interface are analyzed,and the differential equations of fluorescence fluxes are structured,and the solution framework for each differential equation is offered.Thereby,the functional relationship between the fluorescence radiation transfer factor and the concentration of emulsified oil spill is derived.The effectiveness of the proposed model are verified by simulating fluorescence for water-in-oil and oil-in-water at different concentrations exploiting the fluorescence radiation transfer model.Finally,aiming at the problem of evaluating the oil spill thickness for oil-in-water emulsified oil spill on the sea surface,an equivalent evaluation algorithm of oil-in-water spill thickness is proposed.An equivalent evaluation model of oil-in-water spill thickness is designed,and the evaluation problem of oil-in-water spill thickness is transformed into the estimation problem of oil film thickness in an equivalent model with the same fluorescence effect.Based on the LIF detection mechanism and the fluorescence radiation transmission process,the equation of the LIF system receiving the fluorescence signal is established,and then the calculation formula of the oil film thickness is obtained by inversion.Two kinds of oil products,heavy and light,are selected.The effectiveness of the equivalent model are verified through simulation experiments.Meanwhile,the applicable conditions of the equivalent evaluation algorithm are obtained by analyzing the equivalent error.