| Summary: | The idea of constructing the “GNSS-like” seafloor geodetic network for underwater positioning, navigation, and timing (PNT) has been proposed by many countries. Based on this idea, this paper introduces the principle of the seafloor PNT network and provides a combined measurement method, including the absolute positioning and the relative positioning. Experimental results show that the positioning difference between the proposed method and circle-sailing positioning is approximately 10 cm, and the observation efficiency is higher than the existing measurement in the seafloor PNT network. In addition, a model is derived to determine the optimal configuration of the unit network (the basic component of the seafloor PNT network), considering the ranging capability of acoustic beacons, which is helpful to balance the side length of the unit network and the number of observation sessions in the relative positioning. Finally, a chain coordinate transfer strategy in the whole seafloor PNT network is proposed, and the positions where the absolute positioning should be carried out in the whole network are derived based on the conditional adjustment model. Based on this strategy, the design schemes of a seafloor PNT network with centimeter, decimeter, and meter positioning accuracy when the acoustic velocity measuring accuracy is 0.02 m/s and the time measuring accuracy is 10<sup>−5</sup> s, are given in the experimental section.
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