Modeling of acoustic propagation across warm-core eddies

Abstract

A theoretical investigation has been made into the effect on acoustic propagation of oceanic fronts at the edge of warm-core eddies. The investigation utilized modeling of acoustic propagation using the parabolic approximation to the wave equation. Propagation was examined using typical parameters for a wintertime warm-core eddy in the Tasman Sea. Propagation across the eddy boundary (at a frequency of 100 Hz) is shown to create a second series of convergence zones, in addition to the normal series. This occurred for propagation both into and out of the eddy. For a source outside the eddy, energy is shown to strongly couple from deep refracted paths to mixed layer paths within the eddy. The eddy boundary was found to have significant effects on convergence zone properties. Acoustic propagation was also modeled using parameters from a particular realization of a summertime warm-core eddy in the Tasman Sea (for which realization there was environmental and acoustic data available). This eddy had a surface duct and a separate subsurface duct. Reasonable agreement between model and experiment was found for source and receiver both in the subsurface duct at frequencies from 50 to 1000 Hz; disagreement occurred at 25 Hz. However, for source in surface duct but receiver in subsurface duct, the agreement was poor at most frequencies. The effect of minor variations in oceanic and experimental parameters was examined to determine the experimental resolution required of these parameters.