Research On Oil Film Thickness Inversion Algorithm In Continuous Area Of Oil Spill Based On LIF

With the increasingly serious problem of marine oil spill,oil spill on the sea has become one of the most serious problems of marine pollution,rapid and efficient oil spill detection is of great significance to the protection and restoration of marine ecological environment.Laser induced fluorescence(LIF)technology is considered to be one of the most effective oil spill detection technologies.However,LIF based oil spill detection is still in the research stage,and a complete theory and method of oil spill detection has not been established,Therefore,it has certain theoretical significance and application prospect to develop an efficient method for detecting oil spill on the sea surface and an algorithm for analyzing and processing the detected data.The main research contents and results are as follows:Firstly,the principle of LIF detection and the influencing factors of fluorescence intensity are analyzed,and the attenuation effect of laser in the transmission process of atmosphere,oil film and sea water is discussed.According to the principle of LIF detection and the characteristics of laser transmission,the lidar equation of oil spill on the sea surface is summarized and derived.Secondly,the spectrum acquisition experiment is carried out,and the best spectrum acquisition scheme is determined based on the comprehensive consideration of the spectrum signal quality and detection speed.Aiming at the problem that the fluorescence signal is easily disturbed by noise in the detection of oil spill on the sea,a threshold denoising algorithm based on lifting wavelet transform is proposed,and the experimental analysis is carried out.The collected spectra are corrected,and spectral data sharing and reuse are realized by interpolation and Raman correction.Thirdly,an oil film thickness inversion algorithm based on the two-band ratio model is proposed based on the invariable oil film fluorescence signal waveform under different detection conditions.Two bands with different optical coefficients were selected to calculate the ratio of fluorescence signal intensity.The ratio gradually changed with the increase of oil film thickness and eventually tended to a fixed value,while the ratio remained unchanged for oil film with the same thickness.In this paper,the oil film thickness is retrieved by setting up a lookup table of two-band ratio and oil film thickness,and the effectiveness of the algorithm is verified by experiments.Then,aiming at the limitations and shortcomings of the integral Raman method for oil film thickness inversion,an oil film thickness inversion algorithm combining Raman scattering light and fluorescence signal was proposed.Based on the results of oil film thickness inversion from thin film Raman scattering light signal,the fluorescence characteristic spectrum of oil spill is obtained by iterative approximation method,and the oil film fluorescence signal is used to retrieve the oil film thickness.The experimental results show that the proposed method can effectively retrieve the oil film thickness,and the inversion results have high accuracy.Finally,an oil film thickness inversion algorithm based on waveform matching is proposed.The spectral signal was regarded as the superposition of the oil spill fluorescence signal,the seawater background fluorescence and the Raman scattering light signal.The influence of spectral intensity was eliminated by the normalization process,and the minimum residual was calculated and the oil film thickness was retrieved by the iterative approximation method.In order to solve the shortcoming of the iterative approximation algorithm,an improved particle swarm optimization(PSO)algorithm is proposed to improve the running efficiency of the inversion algorithm.The experimental results show that the proposed method can greatly improve the detection speed,the improved particle swarm optimization algorithm has higher operating efficiency and the inversion results have higher accuracy.