MODELING THE BASIC ARRIVAL STRUCTURE OF A 400 Hz ACOUSTIC PULSE THROUGH THE SOUTH CHINA SEA BASIN

Abstract

As part of the Windy Island Soliton Experiment (WISE), a sound source and a receiver were moored on two deep-water moorings, 167-km apart, in the northeastern South China Sea basin. The source transmitted phase-modulated acoustic signals with a carrier frequency of 400 Hz for approximately one year. The receptions thus captured the multi-scale variability in the signal transmissions induced by the ocean mesoscale variability and the progression of the transbasin ocean internal tides and waves. A numerical two-dimensional acoustic propagation model based on Hamiltonian ray tracing is utilized to replicate the observed basic arrival structure and transmission loss. Being able to accurately model the basic arrival structure is a necessary first step before modeling the observed variability can be attempted. The comparison of the modeled arrival structure with the actual data is utilized to refine the angular resolution of the ray fan in the model, to estimate the geo-acoustic properties of the bottom, and to develop transmission loss estimates. Transmission loss measurements obtained from several sonobuoys deployed along the transmission path are used as an independent metric to evaluate the model.