The potential of linear polarization for backscatter-blocking and comparison to range-gated technologies focusing on maritime applications

In the maritime domain, fog represents a significant challenge, e.g. for the detection of castaways in search and rescue missions or obstacle avoidance/warning systems, particularly at night. In scattering environments, conventional active imaging techniques often struggle due to backscattering resulting in low contrasts or completely saturated pixels from backscattering at fog particles (water droplets). The effective suppression of atmospheric backscatter in foggy environments by using Gated-Viewing technology has been demonstrated in previous studies. However, another alternative of blocking backscattered light is using polarization if the scattering event preserves polarization, which is the case for water droplets (maritime fog). In the present study, we modified an existing, unpolarized light emitting Gated-Viewing instrument and added the option to emit and receive linear polarized light through installation of polarization filters. All images taken with this modification are acquired in Continuous Exposure (CE) mode, i.e. without gating. The objective was to investigate whether polarization can serve as an alternative to Gated-Viewing in the maritime domain where backscatter is expected to largely preserve polarization. In initial field tests the efficiency of the modified (polarized) instrument in suppressing retroreflections under clear weather conditions was evaluated. Further tests with artificial fog showed that the modified instrument could effectively suppress backscatter, achieving a contrast loss comparable to that observed in clear weather conditions.