Polarization Characteristics of Multi-Angle Visible Light of Oil Spill Target in Rough Water Environment

Wei Zhang; Juntong Zhan; Su Zhang; Qiang Fu; Yingchao Li; Jin Duan; Shicheng Bao; Huilin Jiang

doi:10.3788/AOS221428

Abstract

Results and Discussions The linear polarization of different oil spills is different, but the general law remains the same. When the incident zenith angle is unchanged and the relative azimuth is 180°, the linear polarization tends to increase first and then decrease with the increase in the observed zenith angle (Fig. 6). When the incident zenith angle is constant, the degree of linear polarization also tends to increase first and then decrease with the increase in the observed zenith angle (Fig. 10). The degree of linear polarization rises before it declines as the relative azimuth grows, and it reaches the maximum at the relative azimuth of 180°. The linear polarization degree is high in the relative azimuth angle range of 120°–240° and low otherwise (Fig. 7). In addition, the improved pBRDF model of oil spills has high confidence accuracy, which is more than 80% (Tables 2-5).The relationships between the linear polarization and the incident zenith angle, observation zenith angle, relative azimuth, and wavelength are studied. The results indicate that the incident zenith angle, observation zenith angle, relative azimuth, and wavelength have an impact on the linear polarization of oil spills. The linear polarization increases slightly with the increase of wavelength in the visible light range, but the linear polarization of the observation zenith angle and relative azimuth barely changes relative to that of the incident zenith angle. The linear polarization tends to increase first and then decrease as the relative azimuth rises, and the peak appears at the relative azimuth of 180°. At this time, the same trend of linear polarization holds as the observation zenith angle and the incident zenith angle grow, and the contrast is high. When the relative azimuth is 0°, the linear polarization registers the smallest when the incident zenith angle is equal to the observed zenith angle. The construction of the pBRDF model for oil spills on the sea surface and the investigation of the influence of the incident zenith angle, observation zenith angle, relative azimuth, and wavelength on linear polarization are conducive to realizing the accurate detection of oil spills on the sea surface and can provide a reference in this regard. The model and experimental scheme will be further optimized to study the influence of temperature on the linear polarization of oil spills and build a more accurate model.Objective

Oil spill pollution has caused great harm to the marine environment and human society. Accurate identification of marine oil spills can help formulate oil spill treatment strategies and assess disaster losses. Optical characteristics, essential characteristics of marine targets, can reflect the physical and chemical properties, geometric surface, and other characteristic information of marine targets from the aspects of wavelength (frequency), energy, phase angle, polarization state, scattering or radiation characteristics, etc. In addition to the intensity, spectrum, and multi-angle detection methods, there is also polarization information in the reflected radiation of the detected target. When the light wave interacts with the surface of seawater, oil film, and other media, the polarization characteristics of the reflected light wave will change. Polarization detection has fogged permeability to a certain extent, which can weaken the influence of sea fog, significantly improve the contrast between target and background, and weaken or even eliminate the influence of solar flares. However, research on the polarization detection mechanism and the modeling of marine oil spills is still insufficient, which restricts the understanding of polarization characteristics and affects practical applications. Therefore, it is necessary to study the polarization detection mechanism of marine oil spills and build a theoretical model to improve the marine detection ability.

Methods

On the basis of the Priest and Germer (P-G) theory, this study comprehensively considers specular reflection, diffuse reflection, and volume scattering, optimizes the traditional model for oil spills on the sea surface, and proposes a polarized bidirectional reflection distribution function (pBRDF) model for oil spills on the sea surface that includes the scattering part. Then, it tests the polarization characteristics of five different oil spill targets (i.e., engine oil, crude oil, diesel oil, kerosene, and gasoline) in the rough water surface environment. By the comparison of the experimental data with the simulations, the visible light polarization characteristics of different oil spills are obtained, and the correctness of the model is verified.

Conclusions

According to the micro panel theory, this paper comprehensively considers specular reflection, diffuse reflection, and volume scattering, optimizes the traditional model for oil spills on the sea surface, and proposes a pBRDF model of oil spills on the sea surface that includes the scattering part. The model can reduce the error caused by the case only considering specular reflection. The comparison with the experimental data shows that the fitted curve is in good agreement with the measured data, and the model built in this paper is accurate.