Observation of a mesoscale warm eddy impacts acoustic propagation in the slope of the South China Sea

Abstract

Acoustic rays are modified while propagating through oceanic eddies. However, due to the lack of field synchronous observation, the impact of mesoscale eddy on the acoustic propagation is less clarified. To address the issue, an eddy-acoustic synchronous observation (EASO) field experiment for a mesoscale warm eddy was carried out in the slope of the South China Sea (SCS) in October, 2021. During the field experiment, a total of 105 conductivity-temperature-depth (CTD) stations, as well as a zonal acoustic survey line through the center of the warm eddy, were obtained. The vertical structures of temperature and salinity indicate that the warm eddy is surface-intensified with temperature and salinity cores confined within depths from 70 m to 200 m and 10 m to 70 m, respectively. The acoustic observation shows two obvious convergency zones (CZs) at about 39 km and 92 km in the eastern half acoustic line, and one convergency zones (CZ) at about 25 km in the western half acoustic line. By comparing with the none eddy circumstance, the respective impacts of the topography and warm eddy are quantitatively analyzed with a ray-tracing model. The results indicate that the topography shortens the horizontal span of the CZ by 11.4 km, while the warm eddy lengthens it by 1.7 km. Additionally, the warm eddy shallows the depth and broadens the width of the CZ by 32 m and 1.4 km, respectively. The anisotropy of 3D sound fields jointly influenced by the warm eddy and the local topography show that the distance differences of the first CZs in different horizontal directions can be as long as 31 km.

A physics-informed machine learning approach for predicting acoustic convergence zone features from limited mesoscale eddy data

“…On one hand, machine learning relies on establishing input and output datasets for the model, posing a gap in how to introduce suitable features to enhance the model's generalization ability and physical credibility. On the other hand, the CZ waveguide stands as a crucial underwater acoustic propagation mode in the deep ocean environment, significantly impacted by mesoscale eddies (Chen et al, 2022). The current predicament lies in the difficulty faced by vessels traversing far-sea routes within mesoscale eddies to access realtime comprehensive oceanic information pertaining to these phenomena.…”

Reconstruction of the Sound Speed Profile in Typical Sea Areas Based on the Single Empirical Orthogonal Function Regression Method

“…For the in situ observation method, observational instruments, such as Argo buoys, expendable conductivity temperature depth (XCTD) [7], expendable bathythermograph (XBT) [8], and sound velocity profile (SVP) [9], are applied to obtain the hydrological parameters such as T, S, and pressure. Although this method can obtain the highest-accuracy SSP, conducting in situ experiments is difficult because they are resource-and time-consuming endeavors and are performed only by a small number of communities [10][11][12].…”