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 fr equencies in the 100-500 Hz range) encompass a variety of different sc ales: the water column varies smoothly over many wavelengths, whereas the seafloor is rough at scales from 1 m to several kilometers. We pre sent 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 computa tions tractable and assures high accuracy. The technique, which we cal l 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 fi eld is inserted into a viscoelastic finite difference grid on which th e complex acoustic/anelastic interaction of the wave field with the ro ugh seafloor is computed. The backscattered wave field collected on hy pothetical vertical and horizontal lines is then extrapolated by means of the Kirchhoff integral to a receiver array distant from the scatte ring locale. The fidelity of the method is demonstrated by comparison with solutions from a WKBJ approximation method and full finite differ ence simulations.