A full-field time-domain model for reverberation in complex environments and waveguides with rough interfaces

Abstract

A full-field perturbation approach [Ivakin 2016] has been used for modeling reverberation at given frequency in spatially varying layered environments and waveguides with rough interfaces. Average reverberation intensity was shown to be related with a local Bragg-wavenumber power spectrum of roughness through integration over the reference (unperturbed or smoothed) interfaces. The integrand includes a factor, a two-way propagation/interaction kernel, defined in terms of Green’s function and a local contrast of acoustic parameters at the interfaces. This work extends the approach to time domain and includes additional integration over frequencies with another factor in the integrand, the radiated energy time-frequency distribution (ambiguity function). However, the integration within the signal frequency bandwidth can be significantly simplified using the frequency-range interference invariant. As a result, extremely fast estimations of reverberation time series (codas) can be made which require calculations of Green’s function of the reference medium in the vicinity of the interfaces at only one (central) frequency. Numerical examples for time dependence of narrow- and broad-band reverberation in layered environments and waveguides with rough interfaces using PE-approximation for Green’s function are presented. A possibility for remote monitoring of temporal and spatial variability of ocean interfaces based on propagation and reverberation measurements is discussed. [Work supported by ONR.]