Three-dimensional Flow Mapping for Monitoring Underwater Small-scale Dynamics Using Coastal Acoustic Tomography

In this study, coastal acoustic tomography (CAT) technology was utilized to perform an initial investigation into the observation of underwater small-scale dynamic processes. An underwater monitoring experiment using a CAT network was conducted with four stations at Huangcai Reservoir in Hunan, China. Ray acoustic simulations were employed to match the simulated ray paths of the vertical profile of each pair of trans-ducers to the two identified times of flight (TOFs). To visualize flow field fluctuations caused by the underwater small-scale dynamic processes, an autonomous underwater vehicle (AUV) was deployed to navigate within the observation area. Three-dimensional (3D) inversion techniques were used for multi-layer analyses of the underwater horizontal flow field in the region. The AUV cruising layer’s flow field was mapped and showed consistency with acoustic Doppler current profiler (ADCP) data. The velocity data recorded by the ADCP and CAT were 0.87 m/s and 0.82 m/s, respectively, as the AUV passed by. Additionally, the results were validated through comparison of range-average current measurements and the net inflow error. This study illustrates that the 3D CAT mapping method can effectively reconstruct the 3D flow field, facilitating the observation of underwater small-scale dynamic processes.