Polarization Characterization of Laser-Induced Fluorescence from the Simulated Oil Spill Samples
LUAN Xiao-ning1, ZHANG Feng1, GUO Jin-jia1, CUI Ting-wei2, ZHENG Rong-er1*
1. Optics and Optoelectronics Laboratory, Ocean University of China, Qingdao 266100, China
2. First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China
Abstract：Laser induced fluorescence technique has been considered as one of the most effective means for the detection of marine oil spills, while its feasibility was limited by the fluorescence signal resulted from chlorophyll and CDOM in natural water. To eliminate those influence during the detection, a LIF polarization experimental setup with 532 nm cw-laser was built up and used to investigate the polarization characteristics of LIF spectra of six oil samples with various densities as well as natural water sampled from the pond. It is found that the LIF spectra of all six oil samples possess obvious polarization characteristics, and are significantly different from that of natural water which is totally unpolarized. With this difference, the interference of chlorophyll and CDOM can be excluded. It also reveals that the polarization characteristics of LIF spectra are distinctive among different samples. With the wavelength increasing, the LIF DOP of oil samples decreases gradually under linearly polarized excitation, and the DOP decrease of heavy and light crude are largest and least respectively while that of diesel remains the same. When the polarization states of excitation laser changes cyclically, it is observed that the LIF DOP of all six oil samples oscillate periodically with it in the same trend. With respect to the variation range of the LIF DOP, the medium samples exceed the light samples but are inferior to the heavy ones. So it can be inferred from the results that the wavelength variation as well as excitation polarization response of the LIF DOP of oil samples are highly likely correlated to the density of the sample, which means the polarization characteristics of LIF spectra can be used as auxiliary parameters with which identification of oil spills might be successfully achieved.
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