一种基于荧光信号的海面厚油膜评估方法

油膜厚度是海面溢油污染评估分析的一个重要指标，激光诱导荧光(LIF)技术是目前最有效的海面溢油探测技术之一，基于LIF探测技术的油膜厚度反演算法当下仅有适用于薄油膜(≤10~20 μm)的评估方法，而对于较厚油膜(>20 μm)的评估目前尚无有效的反演算法。鉴于此，提出一种基于LIF技术适用于较厚油膜的反演算法，该算法采用油膜荧光信号反演油膜厚度，推导了油膜厚度反演公式，并给出了基于该反演算法的油膜厚度评估方法。首先采用最大类间方差算法(Otsu)选取合适的荧光光谱波段，然后根据选取波段内每个波长的光谱数据反演油膜厚度，最后采用反演油膜厚度的平均值作为油膜厚度评估结果。研究了该算法的适用范围，给出了该算法有效评估范围最大值与测量相对误差的关系，并结合消光系数给出了在多种测量误差条件下不同消光系数油品有效评估范围的最大值。通过实验对本文方法进行了验证，选用原油和白油的混合油(1∶50)作为实验油品，以波长为405 nm的激光作为激发光源，采集波长范围为420～750 nm，采集了海水背景荧光和拉曼散射光光谱、实验油品的荧光特征光谱和多种不同厚度的较厚油膜的荧光光谱。采用Otsu算法选取420～476 nm波段评估油膜厚度，在实验油品油膜厚度≤800 μm时，该算法对油膜厚度的评估具有较高的精度，平均误差为10.5%；在油膜厚度>800 μm时，平均误差为28.8%，评估误差较大且随油膜厚度的增加快速变大，该实验结果与利用测量相对误差和消光系数的分析结果一致。实验结果表明，该方法可以实现对海面较厚油膜厚度的有效评估，并可以根据测量相对误差和消光系数判断评估结果的有效性。

A Method for Estimating Thick Oil Film on Sea Surface Based on Fluorescence Signal

Oil film thickness is an important indicator for the assessment and analysis of oil spill pollution on the sea surface.Laser-Induced Fluorescence(LIF)is one of the most effective technologies for oil spill detection at present,the oil film thickness inversion algorithm based on LIF is only suitable for thin oil film(≤10~20μm),there is no effective method for the evaluation of thicker oil film(>20μm).In view of this,an inversion algorithm based on LIF detection technology for evaluating thicker oil film is proposed,the algorithm uses oil film fluorescence signal to invert oil film thickness,deduces oil film thickness inversion formula,and gives oil film thickness evaluation method based on the inversion algorithm.First,Otsu algorithm is used to select the appropriate fluorescence spectrum band,and then the oil film thickness is retrieved according to the spectrum data of each wavelength in the selected band,finally,the average value of the retrieved oil film thickness is used as the oil film thickness evaluation result.The applicable range of the algorithm is studied,the relationship between the maximum value of the effective evaluation range of the algorithm and the relative measurement error is given,the maximum value of effective evaluation range of oil with different extinction coefficients under various measurement errors is given.The method in this paper is verified by experiments.The mixture of crude oil and mineral oil(1∶50)is selected as the experimental oil and the laser with a wavelength of 405 nm is used as the excitation source.The collection wavelength range is 420~750 nm.The background fluorescence and Raman scattering spectra of sea water,the fluorescence spectra of experimental oil and various thick oil films are collected to invert the oil film thickness.Otsu algorithm is used to select the band of 420~476 nm to evaluate the oil film thickness.The evaluation results show that when the oil film thickness is≤800μm,the algorithm has high accuracy,with an average error of 10.5%;when the thickness is>800μm,the average error is 28.8%,with a large evaluation error and rapidly increases with the increase of the oil film thickness.The analysis results of relative error and extinction coefficient are consistent with the experimental results.The results show that the method can effectively evaluate the thickness of the thick oil film on the sea surface,and judge the effectiveness of the evaluation results according to the measurement relative error and extinction coefficient.