The polarization patterns of skylight reflected off wave water surface

Abstract

In this paper we propose a model to understand the polarization patterns of skylight when reflected off the surface of waves. The semi-empirical Rayleigh model is used to analyze the polarization of scattered skylight; the Harrison and Coombes model is used to analyze light radiance distribution; and the Cox-Munk model and Mueller matrix are used to analyze reflections from wave surface. First, we calculate the polarization patterns and intensity distribution of light reflected off wave surface. Then we investigate their relationship with incident radiation, solar zenith angle, wind speed and wind direction. Our results show that the polarization patterns of reflected skylight from waves and flat water are different, while skylight reflected on both kinds of water is generally highly polarized at the Brewster angle and the polarization direction is approximately parallel to the water's surface. The backward-reflecting Brewster zone has a relatively low reflectance and a high DOP in all observing directions. This can be used to optimally diminish the reflected skylight and avoid sunglint in ocean optics measurements.

Seasonal variability of upwelling radiance polarization over the Southern Baltic surface

“…In Fig. 4a Polarization patterns of upwelling radiance, combined with reflected off sea surface and water-leaving, differs from those describing only the reflected part (Zhou et al, 2013). They show, that the DoP of reflected radiance component creates the ring at a polar plot called the Brewster zone.…”

“…Lower SZA causes 25 higher transmission into water depths and higher scattering towards the sea surface. This is why DoP distribution of upwelling radiance in winter is more like a polarization pattern of the reflected part presented by Zhou et al (2013) with their ring-shaped Brewster zone.…”

“…Reduction of sun glints to improve the ocean colour retrieval has been studied by Zhou et al (2017) as well as Garaba and Zielinski (2013) and limitation of sky reflections by observation of sea surface at the Brewster angle from the ship board has been examined by Wood and Cunningham (2001) and by Cunningham et al (2002). Polarization distribution of skylight reflected off the rough sea surface has been examined by Zhou et al (2013). They simulated Degree of Polarization (DoP) as well as the Angle of Polarization (AoP) for reflected parts Zhou et al (2013) showed the influence of wind speed and direction on the polarization pattern of reflected radiance.…”

“…Polarization distribution of skylight reflected off the rough sea surface has been examined by Zhou et al (2013). They simulated Degree of Polarization (DoP) as well as the Angle of Polarization (AoP) for reflected parts Zhou et al (2013) showed the influence of wind speed and direction on the polarization pattern of reflected radiance.…”

“…The angular shape of such a zone strongly depends on SZA (see Fig. 10 in Zhou et al (2013)). However, the results of simulations presented here are similar to measurements of above water DoLP of upwelling 5 radiance presented by Freda et al (2015).…”