Acoustic modelling of a transient source in shallow water

Abstract

A desirable requirement for underwater acoustic models is the ability to simulate a transient signal propagating in an ocean waveguide. Relevant broadband signals are generated, for example, by airguns used in seismic exploration, transducers used for underwater communication systems, and vocalizations produced by marine mammals. Single-frequency acoustic models based on ray, mode, wavenumber integration or parabolic equation representations are often used for this purpose by employing a Fourier synthesis method. In this case, the multiple-frequency, bandlimited medium transfer function is filtered by the spectrum of the source and then inverse Fourier transformed to yield the time-domain waveform. In contrast, direct convolution of a source signal with the medium’s impulse response can be carried out in the time domain. In this paper we describe a convolution-based approach using a ray model representation of the propagation whereby each eigenray amplitude is assumed to be independent of frequency but its phase variation is taken into account. As a result, only a single-frequency calculation is required of the ray model at each range. The two methods are subsequently used to simulate a bandlimited transient signal propagating in a shallow-water, lossy-bottom, Pekeris waveguide.