Fluctuations in Acoustic Transmission Loss: Comparisons Between Measured Data and Predictions of the Safari/Parabolic Equation Numerical Models

The results of acoustic transmission loss measurements in a shallow-water area of the North Atlantic have revealed significant fluctuations in the acoustic intensity levels received by a 60-km distant vertical array of hydrophones.The attempt to attribute these fluctuations to easily identifiable properties of the medium is frustrated by the complexity of the latter.An added complication arises from the location of the measurement site in a geographical area characterized by the convergence of two major water masses of differing environmental properties, viz., Arctic water and Atlantic water.Moreover, the resulting Polar oceanic front is not stationary but, rather, oscillates with semidiurnal tidal periodicity.Propagation factors tentatively identified as contributors to the acoustic fluctuation include the steep gradients in environmental parameters arising from the different water masses, changes in water depth, currents, and possibly other effects.Numerical studies were performed in an attempt to determine the general trends expected of the propagation in this environment.In particular, using simplified models of the test environment, computations were made with SAFARI FF? and a wide-angle version of the Parabolic Equation model (IFDPE).Although neither model by itself is entirely adequate for the environment considered, both range dependence and ocean-bottom shear being of interest, the combination does provide some insight into the suspected phenomena.I.