Research On The Difference Of Polarization Bidirectional Reflection In The Optical Detection Of Spilled Oil On The Sea

Abrupt oil spill accidents cause great damage to the marine environment and human economic development.Due to the limited content in scientific and technical research on marine environment monitoring,as well as lack of integrated information system for processing and analyzing data acquired from various sources,it is difificult to obtain accurate data of oil spills timely.Optical detection technology is an effective means for real-time monitoring and quantitative estimates of oil spills on the sea.However,the mixing of oil spills and sea water causes the difference of light intensity signals between the target and background decreasing,which makes it uncertain and difficult to use the optical detection technology to determine oil spills based on image brightness.According to our study,significant differences in polarization characteristics exists between sea water and oil spills,and it is particularly prominent under the model of bidirectional reflectance distribution function(BRDF).The polarized bidirectional reflectance distribution function(pBRDF)is an important theoretical basis for systematically describing the polarization mechanism of targets,which is composed of BRDF and the Mueller matrix in polarization optics.In this study,the path integral technique is used to establish the Mueller matrix model for the interaction between complex light and spilled oil,which is proved effective from experimental measurement.The main findings of the research are summarized as follows:Firstly,pBRDF and its corresponding measurement are proposed.The relationship between the scattering intensity distribution and the surface roughness of the material is introduced from the rough surface scattering theory.The scattering distribution model and the scattering approximation method of rough surface is further analyzed,and the polarization characteristics of the scattered light off the rough surface are derived.Based on the optical radiative transfer function,the radiation intensity,Stokes vector,and vector radiative transfer equations are introduced.The two main components of the transfer equation for oil spill,Rayleigh scattering and spherical Mie scattering,are analyzed in detail.Secondly,analyze the equivalent optical path and fluorescence characteristics in the detection model,compare and sort the characteristic parameters.The optical path of pBRDF of the research are introduced,as well as the advantages of the route.Not only several common polarization optical characteristic parameters,but also some new polarization parameters,the complete depolarization coefficient,polarization index and average polarization coefficient,etc,which are derived from the scattering distribution characteristics of oil spills,are used to determine oil spills on the sea.Analyze the fluorescence excitation path of crude oil,andconstruct a new fluorescence excitation equation.The fluorescence yield index has been deduced,which describes the sum of fluorescence yield of each measurement point,and could feedback the best experimental concentration of crude oils.Then,introduce the experiment platform,the experimental measurement process,the processing and analysis of experimental data.Three kinds of high concentration standard samples(silicon,graphite and polypropylene)are measured,and the error accuracy of measured values and theoretical values has been corrected by the correction residual analysis for the optical system.The accuracy of the experimental platform is improved.According to the experimental design scheme,oil films and emulsified oil samples were measured.The detection algorithm is used to calculate the characteristic parameters from the experimental data,such as amplitude ratio,phase retardation,degree of polarization and complete depolarization coefficient,which may be used for the detection of oil spills on the sea.The Fresnel reflection equation verifies the reliability and accuracy of the theoretical model.The fluorescence yield index of samples are calculated based on the measured data.And at the same concentration,the fluorescence yield index can be based to distinguish the different kinds of oils.Finally,introduce the practical application of the measurement technology in satellite remote sensing.Through experimental measurement and theoretical derivation,the relationship between the degree of polarization,the refractive index of medium and the measuring angle is clarified.The feasibility of oil spill detection based on polarization remote sensing is analyzed by extracting and analyzing the polarimetric information from the spectral data of the oil spills collected by satellites.Principal component analysis(PCA),feature signal extraction,deep learning are used to establish an auto-identification algorithm,which is based on the pBRDF difference of oil spills and seawater.The detection technology based on the pBRDF is studied,which solves the difficulties existing in optical detection of marine spilled oil and expands detection algorithm for target feature parameter extraction and analysis.The technology proposed was tested by experiments and put into application demonstration.It can provide technical support and serve as reference method for optical detection of marine spilled oil in the future.