Exact modeling of targets in littoral environments

The OASIS and MPL-SIO team will develop an exact 3D time-domain finite difference (TDFD) code for the near-target scattering from a complex elastic object embedded in the littoral environment. The approach for this time-domain code is based on a staggered grid, pseudo-spectral finite difference scheme. In order to accommodate the broken symmetry as well as any subsequent range dependence, a normal mode Parabolic Equation (PE) approach will be implemented to march the solution out to significant range from the scatterer. To couple these two computational methods, the acoustic field calculated by the TDFD code will be projected onto the vertical normal modes of the PE to preserve the complex effects of the scatterer as well as boundary interaction. To handle the field at the boundaries of the relatively small (< water depth) computational domain, we’ll implement the Perfectly Matched Layer approach. In order to run realistic targets at operational frequencies, optimal use of computer resources is required, and we’ll adapt the 3D-TDFD code to run on multi-processor stand-alone machines. A pair of numerical tests will be conducted with the broadband array response for the direct blast (source-receiver) and scattered field (source-target-receiver) from an AUV and a large marine mammal.