On the Effect of Horizontal Refraction Caused by an Anticyclonic Eddy in the Case of Long-Range Sound Propagation in the Sea of Japan

Abstract

The precision of acoustic ranging and navigation depends on the accuracy of the information about the sound speed field in the area of interest. Large-scale inhomogeneities in the bottom relief and water column can significantly affect the horizontal rays corresponding to vertical modes (in the framework of Burridge–Weinberg formalism), which can lead to delays in the acoustic signal modal components, as compared to propagation along the geodesics on the Earth’s surface. In this study, the influence of horizontal refraction on the delay times of the modal components is considered. In particular, it is studied to what extent the presence of a synoptic eddy near the source–receiver path increases the effective propagation distances due to horizontal refraction. The elongation of horizontal eigenrays relative to the geodesic connecting the source and the receiver is also estimated. The influence of hydrological inhomogeneities on the propagation time of different modal components of a broadband acoustic signal is investigated. This is accomplished by the integration of the group slowness (reciprocal to the group speed) along the horizontal eigenrays connecting the locations of the source and the receiver. Implications for improving the accuracy of the solution of acoustic ranging problems are discussed.

Keywords

• underwater acoustics
• normal modes
• modal delays
• eigenrays
• acoustic ranging
• acoustic navigation