Underwater Autonomous Geolocalization Using Time Differential Polarization Field Against Measurement Deviations

Underwater polarization (POL) fields contain spatial information about the Sun. It offers underwater POL fields the capability of navigation and positioning. Benefiting from the advantages of autonomy, the POL positioning is an effective complement for the global navigation satellite system (GNSS)-denied underwater environment. The current POL-based positioning strategies always exploit the Sun's position directly. However, the solution of geolocalization is susceptible to the constant deviations in Sun measurement. In an effort to address this issue, a two-step positioning model is designed. The Sun's positions over time are calculated by exploiting the POL field inside Snell's window, in which the underwater disturbance can be shielded. Subsequently, the first step in the two-step model adopts time-sequence Suns for coarse positioning. Around the coarse positioning solution, a local region is determined as the precondition for the second step positioning. A time differential Sun (TDS) positioning strategy is proposed for a refined geolocation. TDS exploits the Sun's dynamic movement for positioning, and thereby the position errors arising from the constant deviations are eliminated. An underwater POL positioning system is developed. The experimental results demonstrate that the positioning accuracy is improved distinctly by the TDS strategy.