A hybrid wave propagation simulation technique for ocean acoustic problems

Intermediate range bottom interacting deep ocean acoustic experiments (up to similar to 50 km offset in water depths exceeding 1 km using frequencies in the 100-500 Hz range) encompass a variety of different scales: the water column varies smoothly over many wavelengths, whereas the seafloor is rough at scales from 1 m to several kilometers. We present a general hybrid technique to solve the two-dimensional acoustic/viscoelastic equations for problems that include these different wave propagation regimes. This approach makes realistic large-scale computations tractable and assures high accuracy. The technique, which we call Hybrid Adaptive Regime Visco-Elastic Simulation Technique (HARVEST), consists of three parts. A Gaussian beam method is used to propagate the source wave field through a vertically varying water column to the scattering region near the seafloor. This extrapolated source wave field is inserted into a viscoelastic finite difference grid on which the complex acoustic/anelastic interaction of the wave field with the rough seafloor is computed. The backscattered wave field collected on hypothetical vertical and horizontal lines is then extrapolated by means of the Kirchhoff integral to a receiver array distant from the scattering locale. The fidelity of the method is demonstrated by comparison with solutions from a WKBJ approximation method and full finite difference simulations.