为实现水面溢油目标的偏振遥感, 选择合适的波段和观测角度, 需要油膜的光谱偏振特性数据作支撑。 在实验室采用椭偏测量的方法, 针对不同厚度机油油膜和纯净水作为背景样本, 测量了不同观测角度下从紫外到近红外波段(270~900 nm)的镜面反射光谱偏振参数: 辅助角 ψ和相位差 Δ, 并对在相同条件下油和水的测量结果作对比。 分析表明除布儒斯特角附近位置外, 不同厚度的油膜与水的起偏特性在各观测角都存在差异。 通过在45°入射角所测的 ψ和 Δ, 得到水/油样本的光谱折射率和消光系数, 水折射率经过偏移修正后, 与Schiebener水折射率模型的标准差为3×10^-5。 根据之前得到的油/水参数, 对油膜在水背景的物理现象作薄油膜理想介质层建模, 用菲涅耳定律仿真自然光的镜面反射, 发现在全观测波段相同入射光条件下油膜的反射光存在明显的偏振度(DOP)或偏振角(AOP)光谱偏振可观测性。 模型与实际测量结果对比发现: 在300~350 nm仿真结果和实际测量相符, 油膜的反射光偏振性质趋近于油样本; 在350~550 nm, 油膜模型仿真结果比实验的干涉效应更明显, 油膜实验数据表明其光谱起偏性质依然与油保持一致; 在大于550 nm直到近红外波段, 实验干涉效应开始显著。 说明油膜比油有更强的散射或吸收特性, 辨识参数得到油膜的消光系数存在不同于油的随波长先变小后变大的性质。 总之, 利用光谱椭偏测量方法, 通过多波段、 多角度测量, 分析液体样本的光谱偏振特性和折射率等性质; 偏振观测的恰当角度与油/水的布儒斯特角有关, 在布鲁斯特角之外的位置观测, 油膜的光谱椭偏角相较水都存在分辨能力; 对小于200 μm的薄油膜近红外波段可重复性较差, 而紫外和可见蓝紫波段相比之下有很好的可重复性和区分性, 更适合于对甚薄油膜表面种类的遥感观测。 该实验涉及的方法可以用于其他油种油膜的偏振光谱测量, 实验数据为偏振遥感工作的波段选择与观测角度提供提供参考。

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.