## 4 Conclusions  
Our study proposes an underwater geodetic network configuration consisting of three seafloor base stations, one underwater subsurface buoy, and one sea surface buoy. The  
Figure 9: Signal transmission loss. (**a,b**) Signal transmission loss of the base station at 500 m depth and its variation with distance and depth; (**c,d**) signal transmission loss of the base station at 2998 m depth and its variation with distance and depth. Blue, orange, yellow, purple, and green colors in subfigures (**b,d**) denote user depths of 100 m, 500 m, 1000 m, 2500 m, and 2900 m, respectively.  
main purpose of the UGN is to provide kinematic positioning for regional underwater submersibles for ocean near-bottom surveying and precision engineering. To evaluate the performance of the network configuration, the positioning range and accuracy were analyzed by changing the seafloor base station separation and subsurface buoy height. The simulation results indicated that, in a deep-sea environment with a water depth of 3000 m, the positioning accuracy and range were mainly affected by the distance between the seafloor base stations, and the height of the subsurface buoy had a greater impact on the positioning accuracy than on the positioning range. In general, when the distance between seafloor base stations was 9-13 km and the height of the subsurface buoy above the seafloor was lower than 2.5 km, the configuration had the optimal kinematic positioning performance, which could achieve a submersible positioning accuracy of less than 30 m within an underwater space of 25 km \(\times\) 25 km \(\times\) 3 km. Compared with the network configurations with fewer or more stations, the proposed configuration with the underwater subsurface buoy and the sea surface buoy made the kinematic positioning performance of the UGN more precise and cost-effective.  
The purpose of our study was to evaluate the configuration of UGNs on kinematic positioning performance. Based on the proposed evaluation method in this study, an optimal network configuration with the best positioning performance can be obtained under various conditions, such as the effective sonar ranging distance and accuracy, the water depth, and the underwater base station configuration. However, a variety of other factors, including the underwater acoustic environment, the base station coordinate accuracy, and stability, affect the user kinematic positioning performance, which should be thoroughly investigated in future studies.  
Conceptualization, M.L., Y.L. ([PERSON]), Y.L. ([PERSON]) and Y.H.; methodology, M.L. and Y.L. ([PERSON]); coding, M.L.; validation, M.L., Y.L. ([PERSON]), Y.L. ([PERSON]) and G.C.; formal analysis, M.L., Y.L. ([PERSON]), Y.L. ([PERSON]) and G.C.; writing--original draft preparation, M.L.; writing--review and editing, Y.L. ([PERSON]), Y.L. ([PERSON]), G.C. and Q.T.; visualization, M.L.; supervision, Y.L. ([PERSON]) and Y.L. ([PERSON]); funding acquisition, Y.L. ([PERSON]), Y.L. ([PERSON]) and Y.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China, grant number 2020 YFB0505805, the National Natural Science Foundation of China, grant numbers 42004030 and 41974001, Wenhai Program of the S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology (Qingdao), grant number 2021 WHZZB1002 and Technology Innovation Pilot Program of Shandong Province, grant number 2020 YFB0505800.  
The data presented in this study are available on request from the corresponding author.  
We thank [PERSON] at Ocean University of China for her help in figure generation and analysis. We greatly appreciate the anonymous reviewers for the insightful comments that improved this manuscript greatly.  
The authors declare no conflict of interest.