Sea fog is a particular kind of atmospheric aerosol that often poses hidden risks to ship navigation, ocean exploration, human productivity, and life. In light of the aforementioned issues, this research conducted a thorough investigation of the polarization transmission properties in a sea fog environment. We studied the physical characteristics of sea fog and established a polarized radiative transfer model based on RT3/PolRadtran (polarized radiative transfer) in a sea fog environment based on the theory of Mie scattering. The effects of wavelength, polarization state, sea fog concentration, and salt content on the polarization degree were simulated by using the polarization transport model. An indoor sea fog simulation device was designed and built. The simulation test results were compared with the experimental test results from many aspects, and the existing errors were analyzed so that they could be mutually verified for the overall trend. According to the modeling results, distinct polarization states of light exhibit evident depolarization as the sea fog concentration rises. Overall, circularly polarized light has superior polarization-maintaining properties compared to linearly polarized light under the same contrast settings. The penetrating impact of incoming light in the visible range improves with increasing wavelength, and the amount of salt in sea fog has some bearing on the degree of polarization.

We present both simulated and experimental methods to show the propagation of linear and circular polarization under a settling smoke environment. Simulations and experiments were performed for artificial smoke with typical visible wavelengths under light and a moderate settling smoke environment. Using the Monte Carlo method, we simulate polarization propagation with the particle size, refractive index, wavelength, and the optical length under the settling smoke. Through the real-time measurement of optical length during the settling, the relationship of the settling environment parameters in the experiment and the simulation is established to improve the delay problem of the traditional parameters’ measurement. Both the experimental and the simulated results show that with the increase of the concentration the degree of polarization of the four types of polarization is constantly decreased during the settling. Circular polarization persists better than linear polarization with the higher concentration, and the longer the wavelength, the better the persistence of the circular polarization. This study expands the application range of polarization under a settling smoke environment.

The concentration of smoke in an environment can cause obvious interference to visible light intensity imaging, and it is a non-negligible factor in the polarized imaging of ground-based targets. Smoke particles cause severe scattering of photon intensity, resulting in polarization. In this case, low-visibility targets can be effectively identified by detecting the polarization dimension of targets. However, the polarization transmission of smoke in an environment is unclear, and the theoretical simulation lacks experimental reliability verification. To study this problem, this study constructs a polarization transmission model in a smoke environment and simulates and analyzes the scattering of visible polarized light at 450, 532, and 671 nm under different smoke densities. The optical thickness is determined to establish a reliable connection between the simulation and the external field long optical path test and verify the transmission of polarized light. Results show that the method has a 60% confidence in the polarization transmission model. With the increase in optical thickness, the degree of polarization (DOP) of the three wavelengths in the visible light band decreases, and the DOP of each polarized light decreases. No obvious difference is found between the DOPs of circularly polarized light at 450 nm and linearly polarized light. The DOP of circularly polarized light at 532 nm is 1–5% higher than that of linearly polarized light, 1–10% higher than that of the outdoor test, 1–5% higher than that of circularly polarized light at 671 nm, and 2–15% higher than that of the outdoor test. Therefore, the shorter the wavelength in the visible band, the higher the DOP. With the increase in wavelength, the polarization characteristics of circularly polarized light are gradually better than those of linearly polarized light.

There are many non-spherical particles in the sand-dust and carbonaceous environment of the natural world, but this kind of particles are in most cases approximated by the spheres in the description of the transmission process, which cannot reflect the actual state of the transmission through the particles. For this reason, on the basis of polarization characteristic of spherical particles, a further research is made on the polarization characteristic with different refractive index, effective radius, particle shape, and other parameters of ellipsoid particles. When the non-polarized light is used as the incident light, the T-matrix method is applied to the simulation of the transmission process of the non-spherical particles, and the power-law size distribution is used to describe the size distribution condition of the particles, which is the most effective method to show the whole process of light scattering through non-spherical particles. With this method, the polarization characteristic after the transmission of the ellipsoid particles and the polarization differences between the ellipsoid and spherical particles can be obtained, and at the same time the examples of the sand-dust, marine and carbonaceous aerosols are given to show the validity of the results. Simulation results show that the smaller the real part of the refractive index and the larger the image nary part of the refractive index, the less obvious the polarization character differences between the ellipsoid and spherical particles are. When the effective radius of particle increases, the DOP (degree of polarization) variation of the spherical particles is more obvious than the non-spherical particles, and the maximum values are at the positions of the scattering angles 150 and 120 respectively. When the particle shape is different, the differences between the ellipsoid at diverse vertical-to-horizontal ratio and spherical particles are not obvious if the scattering angle is less than 60, and when the vertical-to-horizontal ratio of the ellipsoid particle is reciprocal, the polarization character of the two kinds of particles becomes the same. Through the analysis above, in the process of transmission, in most circumstances the ellipsoid particles cannot be approximated by spherical particles for computation, and the parameters of the refractive index, effective radius, shape of the ellipsoid particles can all influence the polarization character.

Non-contact and non-destructive polarization 3D imaging uses a passive, single-frame array image to calculate 3D information, making it possible to obtain high-precision 3D information about tunnel cracks, and offering outstanding technical advantages. Based on the introduction of the principle of crack detection with polarization 3D imaging, a tunnel lining crack detection plan was developed and a detection equipment was designed. The method and process of polarization 3D imaging for lining crack detection are described in detail. A model of the impact of the tunnel environment on 3D detection and a method for obtaining absolute information have been established to obtain high-precision 3D information about cracks. In a real tunnel environment, tests were conducted to detect wide cracks, narrow cracks, and artificial cracks. The crack detection accuracy with respect to the crack width was 0.2–0.3 mm, and with respect to crack length was 0.2–0.3 mm. At the same time, crack depth information could be obtained. The present research results can provide technical support for the application of polarization 3D imaging in tunnel crack detection.

目的：为了研究偏振光在椭球细粒子中多次散射的传输特性，建立了以黑碳气溶胶粒子为对象仿真与实验验证系统。方法：采用T矩阵和蒙特卡罗相结合的方法，对偏振光经随机取向椭球细粒子多次散射后的偏振传输特性进行仿真研究，建立半实物模拟测试平台对仿真方法进行验证，采用延长灵芝孢子燃烧时间的方式制备椭球细粒子，分别由马尔文粒度仪和光功率计测试椭球细粒子的尺寸分布和光学厚度，建立实验与仿真间的联系，验证了仿真结果的正确性。结果：结果表明，随着黑碳椭球细粒子浓度的增加，水平、垂直、+45度线偏光和右旋圆偏光的偏振度都随之下降，且三种线偏振光保偏性基本一致；随着浓度的增大，圆偏振光保偏性逐渐优于线偏振光，两者保偏性差距越来越大，在光学厚度3.12时达到最大值，当光学厚度大于3.12时，圆偏光和线偏光的偏振度差值趋于稳定；经计算，仿真与实验结果符合度优于70.84%。结论：本研究结果可扩展偏振探测的环境适用范围，为非球形颗粒物环境下偏振探测的研究提供理论支撑。