Research On Airborne Polarization Detection Of Sea Surface Oil Slick

With the frequent occurrence of oil spill,it is more and more important to monitor the oil slick in time and accurately.Airborne detection technology is widely used in sea surface target detection due to its advantages of high detection accuracy,timeliness and convenience.The traditional airborne detection technology is mainly limited to collecting the light intensity information of the target scene.But with the development of multi-dimensional detection technology such as hyperspectral remote sensing,multi-angle detection and polarization information,it opens up a new way for the application of airborne detection technology.This paper mainly studied the polarization detection theory and method of oil slick,and designed a division of aperture polarization optical system which is suitable for airborne platform.Firstly,the optical characteristics and polarization measurement principle of the oil slick were introduced.Then,the Stokes vector,degree of line polarization(DoLP)and angle of polarization(AoP)were described.After that,based on Fresnel reflection law,the polarization reflection component and DoLP of ideal sea surface were analyzed.Combined with the polarized bidirectional reflectance distribution function(PBRDF),the factors which affect the PBRDF of oil slick such as the solar angle of incidence,the angle of detector observation,sea surface wind speed and direction were analyzed emphatically.Secondly,based on the technical parameters of airborne polarization system,the design scheme of division of aperture polarization optical system with multichannel was established.After that,a reasonable detector was selected.The focal length,field of views and F number of polarization optical system were calculated.According to the theory of perfect optical system,the initial structure of the system was determined,and the relationships between the focal length,off-axis and distance between the front lens and the back split-aperture lens group were analyzed.The aberration correction and optimization were finished by ZEMAX software,and the image quality of the polarization optical system was evaluated.Thirdly,the performance of the polarization optical system was analyzed.The tolerance analysis module of ZEMAX software was used to formulate the reasonable tolerance range.Then,an optical machine model of the polarization system was established by Tracepro software.The veiling glare index was used as the evaluation criterion to analyze the stray radiation of the polarization system.By designing a special structural lens hood to suppress the stray light crosstalk,the veiling glare index was reduced to 3%.Meanwhile,through imaging simulation,the image processing flow of polarization image segmentation,image registration and Stokes parameter calculation were proposed.Finally,The principle experiment was carried out to verify the difference of DoLP between seawater and oil slick.At the same time,the advantages of DoLP images and AoP images in information entropy,edge strength and image resolution were verified by using image quality evaluation algorithm.