A normal mode projection technique for array response synthesis in range-dependent environments.

A method is presented to examine the problem of simulating the beam time series response for an array of arbitrary shape in a range-dependent environment using a combination of parabolic equation (PE) forward modeling and local normal mode analysis. The procedure involves computing the acoustic pressure field as a function of depth, using the PE, at the nominal center location of the array. The field is then decomposed into local complex normal mode amplitudes. These mode amplitudes are used to compute the field response on each array element, via range-independent normal mode theory. Conventional plane-wave beamforming is then applied. It is shown that a single matrix computation can be used to map the field as a function of depth to the beam response as a function of angle. The method is applied to two broadband range-independent examples to demonstrate its accuracy. It is then applied to a shallow-water range-dependent experiment from off the Florida coast and a deep-water range-dependent experiment from sound scattering off a seamount in the open ocean. For both range-dependent examples, the model simulation results reproduce the qualitative features observed in the data.