Progress and Challenges in Marine Subsurface PNT： Theories and Methods

Marine subsurface positioning, navigation and timing (PNT) faces a series of scientific and technical challenges, including: characterization and modeling of marine environment and acoustic observation errors, dynamic evolution of seafloor geodetic datum, and optimal multi-sensor information fusion and resilient navigation. This paper summarizes recent progress by Chinese scholars in marine PNT theories and technologies. Key advancements reviewed include: (1) Ocean sound speed field characterization and acoustic observation environmental error compensation.(2) Seafloor geodetic network observation, time-series fusion processing, and dynamic datum maintenance.(3)Multi-frequency multi-mode acoustic navigation and environmental information augmented navigation, sonar/ inertial navigation system / pressure sensor/Doppler velocity log/gravity-magnetic terrain matching etc. Furthermore, the main challenges and future directions for seafloor geodetic datums and navigation are generalized. This study aims to further explore and discuss refined marine PNT theories and technologies, and to provide a reference for in-depth research and engineering applications of PNT in China.