A Study of Spectral Polarization Properties of Oil Slick with Ellipsometry from Ultraviolet to Near-Infrared
LI Qing-ling1, 2, 3, YIN Da-yi1, 2, 3*
1. University of Chinese Academy of Sciences, Beijing 100049, China
2. Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China
3. Key Laboratory of Infrared System Detection and Imaging Technology, Chinese Academy of Sciences, Shanghai 200083, China
Abstract：To find out whether the oil spill target can be better identified by polarization remote sensing and which spectrum and observing angles are suitable for detection, it is necessary to acquire data of the oil slick spectral polarization properties. In this paper, different oil slicks are made with different thicknesses by a kind of oil on water basis, and a series of experiments are set up in laboratory with ellipsometry to measure the mirror reflective polarization parameters: auxiliary angle Ψ and phase difference Δ from UV to near infrared (270~900 nm). We have changed different viewing angles and compared the result with those of oil and water under the same conditions. The result shows that except for Brewster angle, there exist significant distinctions between oil slick and water at different observation angles. Besides, the spectral refractive indexand extinction coefficient of the pure water/oil samples are obtained by Ψ and Δ at 45°. The water refractive index by the experiment meets the water model by Schiebener with standard deviation 3×10-5 after offset correction. The oil spill is modeled with ideal thin oil film on water basis according to those refractive index and extinction coefficient. The Fresnel theory is used to simulate and calculate the reflective light. The simulation shows the reflective light from oil has distinct degree of polarization (DOP) or polarization angle (AOP) vs. spectral with that from water background. Compared with the experiment results, the model shows the same results at 300~350 nm, which has weak interference effect and the properties are close to the oil’s, whileat 350~550 nm, the amplitude of the interference simulation results is weaker than the experiment result, and until wavelength greater than 550 nm, the clear interference is detected. The fact indicates the more absorption or scattering phenomenon in oil slick than in oil. According to parameter identification, it is true that the extinction coefficient of oil slickhas a first smaller then bigger property with wavelength. To sum up, we found that spectral ellipsometry can be used to measure and analyze the spectral polarization properties and reflection index of liquid samples through multi band and multi angle measurements. Suitable observing angles for polarization to oil spill is related to the Brewster angle of oil/water. At incident angles except for Brewster observation angle, oil film can be distinguished from water. Visible and infrared spectrum are suitable for the interior optical properties of the oil film, while ultraviolet spectrum has good stability and is more suitable for observation of surface optical properties of very thin oil film. The method involved in the experiment can be applied to the polarization spectrum measurement of other oil slicks. The experimental data provide theoretical support and technical reference for the selection of appropriate spectral band and observation angle of water surface oil spill polarization remote sensing.
李清灵，尹达一. 椭偏测量法的油膜紫外可见-近红外光谱光谱偏振特性研究[J]. 光谱学与光谱分析, 2019, 39(06): 1661-1666.
LI Qing-ling, YIN Da-yi. A Study of Spectral Polarization Properties of Oil Slick with Ellipsometry from Ultraviolet to Near-Infrared. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(06): 1661-1666.
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