Utilization of wall reflections for robust long-baseline positioning in multipath environments

In port areas, underwater operations using drones are conducted to reduce manpower and improve efficiency. Since radio waves cannot propagate underwater and visibility is limited, acoustic positioning is essential for acquiring drone location information. However, due to the multipath environment characteristic of port areas, conventional time-of-arrival methods based on detecting the maximum peak are often ineffective. Therefore, we previously developed a method that detects the direct path by integrating the propagation delay profiles from each hydrophone. In this study, we further focus on the fact that hydrophones are often installed near walls. By placing virtual receivers at mirror-image positions, we propose a method that maintains positioning accuracy while reducing the number of hydrophones, through by integrating propagation delay profiles including wall reflections. To evaluate the effectiveness of the proposed method, numerical simulations are conducted using the mirror-image method to reproduce a multipath environment. Results showed that the proportion of regions with a positioning error of below 0.5 m increased from approximately 22% with the existing method to approximately 52% with the proposed method. These findings suggest the method is effective in underwater environments. Future work includes parameter optimization, and field experiments in real sea areas.