Effect of eddy on acoustic propagation from the surface duct perspective

Eddy-acoustical effects were investigated from the surface duct perspective. The presence of the eddy would influence sound propagation in surface duct by modifying the mix layer depth (MLD). Altimetry data along with the Argo profiles were used to obtain statistics of the effects of eddy on MLD. Results suggest that in the Northwestern Pacific Ocean, the mean MLD anomaly brought by warm eddy was 26.7 m and the value was 8.6 m for the cold eddy. Acoustic data from an acoustic experiment conducted in a warm eddy in South China Sea (SCS) were analyzed to study the effects of eddy on surface duct energy leakage (SDEL) phenomenon. Numerical simulation was carried out to study the sensitivity of SDEL on MLD variation. Results suggest that the SDEL phenomenon was highly sensitive to the MLD variation when the frequency was lower than the duct-thickness-related critical frequency. The signal attenuation rate of the SDEL signal received out of the duct related with MLD and frequency were also calculated. Acoustic data collected in the experiment agrees well with the simulation results. Given that the warm eddy would increase the MLD for almost 26.7 m on an average level, it is favorable for SDEL phenomenon.