Polarization vision: A door to an unseen world

Polarization vision (PV), or the sensitivity to the partial polarization and orientation of polarization of partially linearly polarized light (PLPL), is widely spread among marine animals. Humans however are mostly insensitive to polarized light and therefore the information it carries is not readily available to us. Using an imaging polarizer, capable of analyzing the linear polarization characteristics of a full image on a single pixel basis, I studied the distribution of PLPL in various oceanic environments, its reflection from various surfaces, and its use by marine animals. The polarimeter was based on two twisted nematic liquid crystals and a fixed polarizing filter in series in front of a video camera. Results revealed a great complexity in the marine polarized light environment. Further, several animals such as fish, echinoderms, and crustaceans reflected unique polarization patterns. In the horizontal line of view, the background light is more than 30% horizontally polarized. Under these conditions, transparent targets, which depolarize or rotate the orientation of polarization are expected to be conspicuous through PV. Several species of zooplankton were found to depolarize light in such a fashion. In field measurements PV enabled an increase of more than 80% in detection range for transparent depolarizing targets over intensity imaging.