Temporal variability in shallow-water acoustic transmission and its correlation with the environment

The ocean is a complex, highly variable medium of acoustic propagation. Medium-induced variability in the acoustic index of refraction (sound speed) can have significant effects on acoustic propagation. Using the results of SACLANTCEN measurements in two diverse geographical areas, the present paper discusses the correlation between the temporal variability of ocean parameters and the fluctuations in acoustic propagation. Following a discussion of the relevant spatial and temporal scales, brief comments are made on the theoretical approaches to propagation in a random medium. This is followed by a discussion of selected results of measurements in the Mediterranean and in the North Atlantic. It is shown that fluctuations in acoustic transmission loss closely correlate with ocean variability resulting from internal waves, tides, tidally advected changes in water masses, and ocean fine structure.