New calculations of the effect of scattering by hydrosols on the underwater polarization field—Application to marine animals' visual world

Polarized light, not perceived by humans, influences the day-to-day lives of marine animals that are polarization sensitive. Animals use polarized light for different tasks such as orientation, prey-detection and intra-specific communication. In the past, polarization in the marine environment was assumed to be dictated by single scattering by Rayleigh particles, resulting in rather simple pattern. However, recent measurements suggest a more complex dependence, where the value of maximum polarization does not go above 50% even in clear waters and its location shifts from 90 degrees towards higher scattering angles in semi-turbid waters. In this study, we show results from a model that includes non-spherical Rayleigh particles, exact Mie calculations for theoretical and measured size distributions of particles, refraction at the air-water interface, and both single and double scattering. We show that single scattering by non-spherical Rayleigh particles successfully reproduces the general pattern of polarization in clear waters, while the existence of "anomalous" neutral points in such waters can be explained by Mie scattering. In semi-turbid waters, single scattering by Rayleigh particles is not adequate, and Mie scattering by particles of various compositions needs to be considered. Therefore, the content of even clear and semi-turbid waters has a strong influence on the polarization environment there and may have important consequences for polarization vision by marine species.