Polarization Patterns of Transmitted Celestial Light under Wavy Water Surfaces

Passive Polarized Vision for Autonomous Vehicles: A Review

This review article aims to address common research questions in passive polarized vision for robotics. What kind of polarization sensing can we embed into robots? Can we find our geolocation and true north heading by detecting light scattering from the sky as animals do? How should polarization images be related to the physical properties of reflecting surfaces in the context of scene understanding? This review article is divided into three main sections to address these questions, as well as to assist roboticists in identifying future directions in passive polarized vision for robotics. After an introduction, three key interconnected areas will be covered in the following sections: embedded polarization imaging; polarized vision for robotics navigation; and polarized vision for scene understanding. We will then discuss how polarized vision, a type of vision commonly used in the animal kingdom, should be implemented in robotics; this type of vision has not yet been exploited in robotics service. Passive polarized vision could be a supplemental perceptive modality of localization techniques to complement and reinforce more conventional ones.

Sensitivity study on the effect of the optical and physical properties of coated spherical particles on linear polarization in clear to semi-turbid waters

The influence of internal inhomogeneities within hydrosol particles on the polarization characteristics of light is investigated by combining an accurate coated sphere (core-shell) single-scattering model with a radiative transfer model that employs Stokes formalism and considers refraction of direct solar radiation at the air-water interface followed by single scattering. A Junge particle size distribution is assumed. Variations in what we call the "linear polarization phase function" (the degree of linear polarization as a function of scattering angle and the E-vector orientation as a function of scattering angle) are examined as a function of variations in the characteristics of the hydrosol particles. An extensive sensitivity study on the influence of variations in the real and imaginary parts of the refractive index of both the core and shell of the hydrosol particles and on the influences of variations in the ratio between the core radius and shell radius is conducted, varying the values of these parameters over the entire parameter space documented in the literature for actual hydrosol particles. In addition, calculations are conducted for specific parameter combinations in order to demonstrate the influence of some of the most important groups of hydrosols, namely, phytoplankton, gas bubbles, carbonaceous hydrosols, and mineral hydrosols, on the polarization field under water. Variations as a function of solar zenith angle are also investigated. Due to the assumption of single scattering, the results presented are relevant to conditions of low wind speed and a low scattering optical depth and/or low single-scattering albedo within the water body (clear to semi-turbid waters at shallow geometric depths and/or moderate to strong absorption within the water body) outside of Snell's window. Possible implications for aquatic animal polarization vision, for light polarization pollution, and for remote sensing are discussed.