Characterization of biologically-induced ocean reverberation features is key to effectively parameterize acoustic models and thus ultimately improve the detection performance of long-range SONAR systems. In particular, scattering from fish schools can significantly contribute to volume reverberation in the open ocean measured by mid-frequencies tactical SONAR (1kHz-10kHz), especially if the res...

A general asymptotic theory is developed to describe the acoustic response of heavily fluidloaded thin shells in the midfrequency regime between the ring and coincidence frequencies. The method employs the ideas of matched asymptotic expansions and represents the total response as the sum of an outer, or background response, plus an inner or resonant contribution. The theory is developed for th...

Mathematical expressions are derived for the far-field backscattering amplitude spectrum resulting from oblique insonification of an infinite, transversely isotropic elastic cylinder by a plane acoustic wave. The normal-mode solution is based on decoupling of the scalar potential representing the horizontally polarized shear wave from those of the compressional and vertically polarized waves. T...

Our approach is to observe both acoustic and microwave backscattering from wind-roughened water surfaces in wind wave tanks, and to model the surface in a manner that will explain both types of scattering. The acoustic and microwave systems used are fully coherent so that Doppler spectra as well as backscattering cross sections can be obtained. Our wave tank arrangements are designed so that th...

Porous media like air-saturated polymer foams with open cells, have a nontrivial frequency-dependent absorption that arises due to viscous and thermal effects at the scale of the rigid frame microstructure. In order to produce multiple scattering at ultrasonic frequencies, mesoscale scatterers are introduced in the porous medium host. The effective wave number of such a multiscale medium should...

The mean and variance of the acoustic field forward propagated through a stratified ocean waveguide containing three-dimensional 3-D random internal waves is modeled using an analytic normal mode formulation. The formulation accounts for the accumulated effects of multiple forward scattering. These lead to redistribution of both coherent and incoherent modal energies, including attenuation and ...

%e have measured the surface-acoustic-wave velocities in Ni/V superlattices using both Brillouin scattering and surface-acoustic-wave techniques; the results are in good quantitative agreement. These results confirm earlier reports of phonon-velocity softening in bcc/fcc superlattices and prove that this is a general phenomenon, not a consequence of the measurement method. In addition, we descr...

This paper describes an analysis of acoustic wave scattering by turbulent premixed flames with moving, convoluted fronts that have random and possibly fractal characteristics. Such interactions play a role in the characteristic unsteadiness observed in turbulent combustion processes. The problem is posed with an integral formulation of the wave equation and assumes that the smallest scales of f...