Variability of acoustic transmissions in the Strait of Gibraltar

Abstract

The Strait of Gibraltar Acoustic Monitoring Experiment was conducted during April–May 1996 to determine the feasibility of using acoustic methods to monitor the transport through the Strait of Gibraltar. Three different approaches to monitoring the flow were explored: (i) Traditional reciprocal ray differential travel times were obtained from three 2-kHz transceivers. (ii) A horizontal array of two 2-kHz receivers was installed on one of the acoustic paths across the Strait to test the feasibility of using horizontal arrival angles (phase differences) due to ray bending by the currents to measure the flow. (iii) A low-frequency (250-Hz) source transmitted to a 350-m vertical receiving array on the opposite side of the Strait to begin to examine the feasibility of using modal analyses, matched-field tomography, and full-field inversion techniques to obtain data on the temperature and current fields. Our initial efforts are aimed at examining the stability of ray and mode propagation and quantifying the accuracy of existing acoustic propagation codes in the complex oceanographic environment that exists in the Strait. Extensive independent measurements of the temperature, salinity, and velocity fields along and perpendicular to the acoustic paths were obtained. [Work supported by ONR.]