模拟溢油样品激光诱导荧光光谱的偏振特性研究

激光诱导荧光是海洋溢油探测的有效手段之一,但该技术的应用易受自然水体中叶绿素、CDOM等物质荧光信号的干扰。为了寻求排除自然水体荧光干扰的方法,基于532nm连续激光器搭建了激光诱导偏振荧光实验装置,并针对六种不同密度的模拟溢油样品和自然水体开展了荧光光谱偏振特性研究。实验结果发现,与自然水体的荧光光谱不具有明显的偏振特性不同,所有模拟溢油样品的诱导荧光均具有明显的偏振特性,这一结论说明激光诱导荧光光谱的偏振特性可以作为排除叶绿素、CDOM等物质荧光干扰的依据。实验还发现,溢油样品的荧光偏振性质因样品种类而异。在线偏振光激发下,原油样品荧光偏振度随波长逐渐降低,其中重质原油样品偏振度降低幅度最大,轻质原油样品幅度最小,而柴油样品荧光偏振度没有明显变化;当周期性改变激发光的偏振状态时,所有模拟溢油样品的荧光偏振度随之发生趋势相同的周期性波动,中质样品荧光偏振度波动的幅度低于重质样品,但明显超过轻质样品。这一结果说明,模拟溢油样品诱导荧光偏振度的波长变化特性及对激发光偏振态的响应特性均与样品密度存在一定关联,其偏振特性可以作为辅助油种识别的重要参量。

Polarization Characterization of Laser-Induced Fluorescence from the Simulated Oil Spill Samples

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.