Mesoscale Eddy Observations and Effect on Sound Propagation in South China Sea 2021

A deep-sea acoustic tomography system was designed and deployed in the northern part of the South China Sea to carry out a large-scale, long-duration deep-sea acoustic tomography experiment during the summer of 2021. Mesoscale eddies were captured in the experiment, reflected in satellite altimeter data, HYCOM data, measured data and results inversed by PIES. Multi-source data are combined here to analyze the movement of mesoscale eddies and induced changes in the depth of the acoustic channel axis. Comparison of the HYCOM data with the measured data shows that there is a large deviation in the HYCOM mode in the presence of mesoscale eddies, with a maximum temperature deviation of $1.9431^{\circ}\mathrm{C}$. In the presence of mesoscale eddies, it is worth exploring the incorporation of acoustic data to improve the HYCOM accuracy in subsequent studies. Based on the ray model, the variations of acoustic propagation losses and acoustic arrival time are investigated when mesoscale eddies passed by. The propagation loss at the same depth is reduced due to the fact that the isotherm falls under the influence of a warm eddy, causing the acoustic channel axis to bend downward. However, its effects on acoustic arrival times need to be further explored.