Experimental And Simulation Analysis Of BRDF And Fluorescence Characteristics Of Natural Water

With the continuous improvement of science and technology,the progress of world industrialization is rapid.People’s development and utilization of the ocean is increasing,and the ensuing marine environmental problems are becoming more and more serious.Human activities and industrial production have brought a series of irreversible changes to the ocean.The eutrophication of the oceans and oil spills have greatly damaged the marine environment.In view of the problems of natural water eutrophication and crude oil leakage,this paper studies the bidirectional reflection distribution function(BRDF)and fluorescence effect of natural water from two aspects:chlorophyll a and crude oil pollution.A method combining reflection characteristics and fluorescence characteristics is proposed to monitor water pollution more accurately.In this paper,the Monte Carlo method is used to establish a photon propagation model in the medium,and the photon propagation process in natural water is simulated.The Rayleigh scattering phase function was used to simulate the spectral reflection characteristics of pure water,and the effects of wavelength,angle of incidence and other factors on the spectral reflection characteristics of pure water were studied.Through simulation analysis,the most suitable band for monitoring chlorophyll a content is 560-640 nm.BRDF simulations were carried out on seawater and oily water bodies with different chlorophyll a content,and the BRDF distribution of oily seawater and clean seawater was compared.The BRDF value of seawater with chlorophyll a content of 15 mg/m~3 at 660 nm wavelength was measured and compared with the simulated value.Different concentrations of crude oil emulsion mixtures were used to measure BRDF at multiple wavelengths.Through the study of BRDF in natural water,it is found that as the content of chlorophyll a increases,the BRDF value also increases,and the oil content and wavelength of crude oil have regular effects on BRDF in natural water.The BRDF value can be used as an important indicator for water pollution monitoring.The fluorescence effect of seawater with chlorophyll a content of 1-25 mg/m~3was simulated by Monte Carlo method.The results show that the detection angle is between[-50°,50°],and a strong fluorescence signal can be obtained.And the higher the concentration of chlorophyll a in seawater,the stronger the fluorescence characteristics of seawater.The fluorescence effect of the crude oil film floating on the water surface was simulated,and it was found that the peak fluorescence reflectance of the oil film and the corresponding emission wavelength were significantly different for different excitation wavelengths.When the excitation wavelengths are 400 nm,425 nm and 450 nm,the emission wavelengths corresponding to the peaks of fluorescence reflectance are 460 nm,440 nm and 480nm,respectively.In this paper,the BRDF of chlorophyll a-containing seawater and crude oil emulsion was experimentally measured,and the reflection and fluorescence characteristics of natural water bodies were simulated.Finally,the law of the influence of chlorophyll a and crude oil on BRDF and fluorescence characteristics of natural water was obtained.A method of combining reflection and fluorescence signals to monitor pollution of natural water bodies is proposed.The strong BRDF signal and the uniqueness of the fluorescence spectrum of each pollutant make the monitoring results more accurate.