Scattered field formulation applied to 3D models for buried targets

Abstract

Calculation of the acoustic scattering from buried targets in a seafloor environment is a task ideally suited for finite element software. A complication arises though when the target’s environment is modeled as two infinite half spaces of water and sediment, each surrounded by perfectly matched layers (PML’s) to satisfy the Sommerfeld radiation condition. Each half space requires a surrounding PML tailored to its material properties, resulting in abrupt discontinuities in PML structure at the corners where the sand-water interface meets the edges of the physical domain. Acoustic energy incident on these corners results in nonphysical reflections directed back into the physical domain. It has previously been shown in a 2D axisymmetric geometry [Zampolli et al., JASA 122, 2007] that using a scattered field formulation, where the incident, reflected, and transmitted fields are applied as background fields, bypasses the discontinuity and eliminates these spurious reflections. Here, the theory is extended to full 3D geometries, allowing the scattering from 3D buried objects to be evaluated and tested against experimental and analytical benchmark results. Once complete, the 3D model template is easily modified to consider any target at any level of burial. [Work supported by Applied Research Laboratories IR&D and ONR, Ocean Acoustics.]