Design of an Imaging Polarized Skylight Compass Using Mechanical Rotation

Abstract

This study introduces the design and implementation of an innovative imaging polarized skylight compass (PSC) based on mechanical rotating components. The device employs a stepper motor to drive the polarizer, facilitating rapid and uniform rotation in front of the camera lens for efficient polarization imaging. The mechanical rotating components are fabricated using 3-D printing technology, which enhances its engineering application capabilities. To mitigate angle errors arising from the rotating mechanism, we propose an optimal robust measurement method based on Newton–Gauss iterations. The method utilizes the intensity images from four distinct polarization directions in consecutive compass output frames to estimate the rotation angle and skylight polarization information. Even in the presence of notable errors in the detected rotation angle, the calculated values of rotation angle, polarization angle, and polarization degree reliably converge to their actual values. To assess the performance of the compass, measurements of actual skylight polarization patterns were conducted and compared with polarizing camera measurements and the predictions based on single-scattering Rayleigh theory. The results affirm the compass’s high sensitivity to detecting polarized skylight. Shipborne experiments under optimal weather conditions illustrate that the compass attains a root mean square error (RMSE) of 3.0269° while independently orienting the dynamic heading angle, with an output frequency of 2 Hz. In practical applications, the compass proves capable of providing relatively accurate heading angle information, thus contributing to the advancement of mechanical rotating polarized imaging sensors in the field of polarized navigation.