Characterization of multi-wavelength polarized light transmission in the real sea spray environment

Sea spray particles are a type of non-uniform, non-spherical, non-isotropic, and complex medium, and the study of the transmission characteristics of polarized light in a real sea spray environment can provide reference values in many fields, such as polarization imaging, marine target detection, and LiDAR, which can make up for the vacancy of polarized light transmission in a complex sea spray environment. In this paper, a real sea fog test is carried out in the Qingdao Sea area of China in the horizontal/oblique direction, and a platform for generating and detecting polarized light with multiple tilt angles is constructed by using the active test method, which realizes the test scheme for the characteristics of energy change and polarization state change in the linearly polarized light and circularly polarized light at different visibility levels in sea fog environments. The results show that it is more difficult to deflect the circularly polarized light than linearly polarized light at the same sea spray visibility level. With the increase in the tilt angle, a decrease in the polarization is observed. The polarization of the near-infrared light is always larger than that of the visible light, which indicates that the circularly polarized light has better polarization preservation than the linearly polarized light and the polarization preservation of the near-infrared light is better than that of the visible light

Multiple Scattering Properties Based on Modified Microsurface pBRDF Model

Scattering polarization properties are one of the main characteristics of a target. Different material types of the target surface can be expressed by the scattering polarization properties, and the use of polarization to characterise the target more effectively is a highly interesting topic. However, the existing polarized bidirectional reflection distribution function (pBRDF) based on microfacet theory for modelling light transmission over rough surfaces is not general. Modelling the scattering phenomena accurately on microsurfaces from a single specularly polarized reflection to full consideration of diffuse polarization remains a challenging task. In this work, we further introduce a directional diffuse reflection lobe to completely define the polarization properties of light in scattering, and revisit the microsurface in the masking and shadowing function part of the model, expanding the traditional symmetric V-groove structure, which is complemented by an asymmetric V-groove structure to improve the accuracy of the model description. We verify through a series of simulations and experiments that our model is in better agreement with the actual truth and that it is more suitable for describing the scattering polarization properties of most targets

Polarization Transmission of Visible Light in Inhomogeneous Sea Fog Particle Environment

Sea fog is a weather phenomenon suspended in the ocean-atmosphere boundary layer. This phenomenon makes the horizontal visibility of the sea atmosphere less than 1 km. Sea fog reduces sea surface visibility. Moreover, the inhomogeneous sea fog particles in the transmission channel result in the absorption and scattering of photons, which seriously affect the performance of optical detection instruments. Polarization imaging detection can solve this problem. However, the evolution law of transmission characteristics between polarized light and inhomogeneous sea fog particles remains unclear. Therefore, we use the equivalent analysis method to improve Monte Carlo, and finally construct the inhomogeneous particle scattering model. The influence of wavelength and relative humidity on DOP (Degree of Polarization) was calculated by the model. The simulated sea fog was created using brine with a preset concentration, and then established an experimental system close to the actual sea fog environment. Indoor polarized light transmission experiments verified the inhomogeneous particle scattering model. Results showed that the accuracy of the inhomogeneous particle scattering model can reach more than 75%. In the visible band, the DOP decreases with the wavelength increase. DOP450 (Degree of Polarization at 450nm wavelength) is approximately 3–10% higher than DOP532, and DOP532 is approximately 5% higher than DOP671. The relative humidity increases from 45% to 85%, and DOP increases by 10–15%. Therefore, in the visible band, the wavelength and relative humidity are inversely proportional to DOP

Study of Sea Fog Environment Polarization Transmission Characteristics

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

Design and Experimental Analysis of Micropolarization Array Based on a Long-Wave Infrared Optical System

Aiming at the shortcomings of the traditional infrared polarization imaging device, such as large volume, complex structure, difficult registration, and inability to recognize moving targets, this paper proposes an infrared polarization imaging method based on a micropolarizer. The long refractive wave infrared polarization optical system is designed to achieve the imaging detection of a 0.25 m target at 1 km; for this, a design of a micropolarizer array suitable for the long-wave infrared band is proposed. In the simulation analysis, the effects of the grating substrate and line grating material, grating period, duty cycle, and grating slot depth on the polarization performance of grating are discussed, respectively. Through infrared polarization imaging experiments on typical targets, the unique advantages of infrared polarization technology in distinguishing metal and non-metal, natural and artificial objects, and high-temperature object recognition are verified, which provides practical support for physical evidence searches and camouflage target recognition

Design and Experimental Analysis of Micropolarization Array Based on a Long-Wave Infrared Optical System

Aiming at the shortcomings of the traditional infrared polarization imaging device, such as large volume, complex structure, difficult registration, and inability to recognize moving targets, this paper proposes an infrared polarization imaging method based on a micropolarizer. The long refractive wave infrared polarization optical system is designed to achieve the imaging detection of a 0.25 m target at 1 km; for this, a design of a micropolarizer array suitable for the long-wave infrared band is proposed. In the simulation analysis, the effects of the grating substrate and line grating material, grating period, duty cycle, and grating slot depth on the polarization performance of grating are discussed, respectively. Through infrared polarization imaging experiments on typical targets, the unique advantages of infrared polarization technology in distinguishing metal and non-metal, natural and artificial objects, and high-temperature object recognition are verified, which provides practical support for physical evidence searches and camouflage target recognition

Multi-Band Polarization Imaging in a Harsh Sea Fog Environment

Researchers in many nations are focusing more on the growth and usage of the marine field, and it is apparent that study on the marine field will be the future development trend. The present study adopts the idea of polarization imaging based on liquid crystal phase retarder as a solution to the drawbacks of conventional industrial camera imaging clarity. Various optical thicknesses are employed to characterize the sea fog concentration; an outside optical imaging equipment is constructed for sea fog imaging research; and pictures comprising polarization characteristics may be determined through image processing. Using multi-band as factors, the benefit of polarization imaging in a sea fog environment is assessed objectively using contrast, information entropy, degree of polarization, and other evaluation indices. The results demonstrate that the quality of the polarization image is superior to that of the intensity image and that the outline of the target is more pronounced in the polarization image. Additionally, the polarization imaging effect is better in the 670 nm band, and the polarization contrast is increased by 1.9%. The contrast trend of the polarization picture is impacted by the time period, but it is roughly equivalent to that of the intensity image. This gives a solid platform for target surveys and civic operations under conditions of dense marine fog

Design and Experiment of High-Resolution Multispectral Polarization Imaging System

This paper addresses the objectives in a complex context: the polarization mathematical and physical model of the basic components of the target/background is constructed by simulation modeling. The image fusion experiment is carried out based on a two-dimensional wavelet transformation. A high-resolution polarization imaging instrument was developed, and static experiments were carried out with polarization, infrared, and visible cameras. The result shows that using polarization imaging detection technology to detect physical evidence targets in complex backgrounds can effectively improve target contrast. It can enrich the target information, improve image quality, and improve target detection accuracy