A novel GNSS-Acoustic positioning model for a seafloor hybrid constellation with fixed and moored beacons

The seafloor hybrid constellation, composed of fixed and moored stations equipped with acoustic beacons, serves as a crucial infrastructure, and holds promising prospects for possible applications in ocean sub-mesoscale current monitoring and acoustic navigation when compared to traditionally unalloyed seafloor constellations. However, most of acoustic positioning models are designed to handle fixed seafloor stations and do not match the actual motion characteristics of moored stations in a hybrid constellation, which may degrade the accuracy of beacon position estimation. To address this gap, a novel GNSS-Acoustic positioning model is proposed in this contribution. Firstly, the critical factor of acoustic measurements, namely observation error of sound speed, is processed by error modelling based on the geometric angle of acoustic rays. Secondly, the smooth variation characteristic of physical marine signal processing is taken into consideration to estimate parameters related to time delay error. Furthermore, the motion depiction of moored beacons is established and introduced into the observation equation system to obtain more reasonable positioning results of seafloor beacons. Finally, the proposed model is validated through tests on a sea-trail experimental dataset, along with an analysis of seafloor baseline measurements. Results and analysis show that, compared with those of traditional methods, the motion of moored beacons can be tracked in detail and the trajectories of the four beacons maintain an overall consistency, which is expected to aid in deriving the possible ocean sub-mesoscale currents.