Abstract
Time-reversal (TR) transmission of the Green's function between a time-reversal mirror (TRM) and a probe source (PS) in an acoustic waveguide produces a spatio-temporal focus at the PS location. The TR focus then behaves as a virtual point source in the outbound direction with respect to the TRM. Further, a collection of adjacent TR focuses may constitute a virtual source array (VSA) that can serve as a remote platform, redirecting the focused field to a selected location beyond the VSA for which the Green's function is not available a priori. The practical limitation to the VSA implementation, however, is the requirement of a PS at multiple adjacent locations to obtain the Green's functions between TRM and VSA. Alternatively, this work proposes the use of a surface ship radiating broadband noise as a PS in conjunction with the waveguide invariant theory, instantly generating a horizontal VSA. The feasibility of remote acoustic illumination using a ship and a TRM is demonstrated using numerical simulations in shallow water.
Highlights
This study considers the use of a ship as a probe source (PS) and a time-reversal mirror (TRM) for remote acoustic illumination in shallow water, which involves several established approaches: time reversal (TR),[1,2] ray-based blind deconvolution (RBD),[3–5] waveguide invariant,[6–8] virtual source array (VSA),[9] and line-of-sight (LOS) beamforming
in an acoustic waveguide produces a spatio-temporal focus at the PS location
The TR focus then behaves as a virtual point source in the outbound direction
Summary
This study considers the use of a ship as a probe source (PS) and a time-reversal mirror (TRM) for remote acoustic illumination in shallow water, which involves several established approaches: time reversal (TR),[1,2] ray-based blind deconvolution (RBD),[3–5] waveguide invariant,[6–8] virtual source array (VSA),[9] and line-of-sight (LOS) beamforming. In TR processing,[2] the transmitted PS signal is received at an array of source-receive elements, referred to as a TRM, and the received signal is time-reversed and backpropagated. Due to the spatial reciprocity and TR invariance of the linear acoustic wave equation, the retransmitted signal converges back to the original PS location.[1] The TR focus behaves as a virtual point source (in the far-field limit) in the outbound direction with respect to the TRM.[10]. In analogy with the guide source concept in astronomy and adapted to shallow ocean waveguides,[11,12] Walker et al.[9] suggested that a collection of adjacent PSs may constitute a VSA that can serve as a remote platform, redirecting the focused field to a nearby location beyond the VSA using LOS wavefront beamforming without the need for a PS at the selected location (see Fig. 1)
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