Analysis of Sound Speed Profile in the South China Sea based on Empirical Orthogonal Function Algorithm

In marine mapping, the sound speed profile (SSP) is an essential parameter. The SSP reflects the characteristics of the ocean sound field’s vertical structure. Furthermore, analyzing the SSP has an important significance on the propagation of underwater sound signals. The empirical orthogonal function (EOF) can extract the SSP data’s main features. It is widely used in SSP fitting and other applications. In this paper, the studying area is 116°~117°E,18°~19°N in the South China Sea. Using the Argo data from 2010 to 2020, this paper first visually analyzes SSP, carries out the EOF’s analysis, and then elaborates the basic EOF principle. It confirms that the EOF has a good application value for the South China Sea, and the first sixth order function can accurately describe the sound speed profile. Then this paper analyzed the EOF’s temporal function. The study found that the third mode of temporal function strongly connects with the ocean’s climate condition. And the two severe fluctuations in 2010 and 2014 have a strong relationship with the typhoon passage. In other words, the degree of extreme fluctuations is positively correlated with typhoon intensity. In brief, understanding the SSP’s temporal pattern is beneficial for applying various engineering scenarios. It can improve the accuracy of sound speed correction of marine acoustic instruments, while the study of marine climate environment has an important role.