Study on skylight polarization patterns over the ocean for polarized light navigation application

Polarized skylight navigation has excellent navigation performance with no error accumulation over time and low susceptibility to interference. The skylight polarization distribution contains rich directional information, such as the solar meridian, the neutral point, and the polarization angle, which plays a key role in the polarization navigation. But up to now the polarizations of both sunlit and moonlit skies have been investigated mainly over the land. In this work, the polarization distribution patterns of the skylight over the East China Sea and the Yellow Sea were studied. The polarization patterns were captured continuously during daytime and nighttime by using a full-sky imaging polarimetry system and then compared with the simulation results using the libRadtran radiative transfer software package. The result shows that the skylight polarization distribution over the sea has almost the same pattern as that on the land. The accuracy of the angle of polarization and the degree of polarization dropped significantly under the cloudy sky. It was found that when the ship sailed on the sea, the direction of the real meridian was close to the solar azimuth during the daytime and close to the lunar azimuth during the nighttime. It was also found that the nautical twilight polarization distribution was affected by both the solar polarization and the lunar polarization, but the solar polarization was dominant. The experiments show that the skylight polarization distribution pattern over the sea can still be applied in the field of polarization navigation. Thus, it is feasible for ships and unmanned aerial vehicles to use the polarized skylight to navigate and orient on the sea.