Analysis of acoustic ray accessibility for underwater positioning service based on seafloor geodetic network

Accurate positioning information is crucial for autonomous underwater vehicles to perform marine surveys and explorations. A seafloor geodetic network is a system of seafloor stations equipped with acoustic transponders that can provide inter-station ranging measurements for SGN absolute calibration, and offer relatively accurate positioning, navigation, and timing information for submarine users within the controlled range. However, the success of the SGN system service relies on the accessibility of acoustic rays for underwater platforms. Due to the intricate ocean environment, the acoustic ray tracks vary with the dynamic sound speed structure, particularly when perturbed by internal waves. This study depicts the tracks of acoustic rays for seafloor inter-station ranging and for locating submarine users, respectively. And the acoustic ray tracks with and without considering the fluctuation of the sound speed structure caused by diffusing and solitary internal waves are compared. Further, we evaluate the geometric positioning accuracy and presents the statistical distribution of a reliable zone for autonomous underwater vehicle (AUV). The analysis of acoustic ray accessibility and the evaluation of positioning accuracy could facilitate the establishment of an actual SGN system and perhaps prevent blind spots for AUVs when utilizing the SGN service.