The value of multi-dimensional arrays and matched-field processing (MFP) in highly anisotropic noise environments

Abstract

In typical littoral environments, below 1 kHz the acoustic noise field is highly anisotropic, and consists of two components. The first and louder component is generated mainly by surface ships and is highly anisotropic in the horizontal with a more modest anisotropy in the vertical. The second component is a quieter wind noise component with a modest vertical anisotropy and little horizontal anisotropy. These typical littoral environments are usually (but not always) characterized as downward refracting with a fast bottom. Simultaneous exploitation of both the vertical and horizontal anisotropy of the ambient acoustic background is possible using MFP with multi-dimensional arrays. A typical scenario in a high shipping noise environment is examined using a dynamic simulation over a two hour period. The simulations used different array configurations: horizontal array, tilted line array, multiple-line towed arrays, and a small number of fixed vertical line arrays, with the same number of elements in an identical noise environment. Several different beamforming approaches were considered including shaded plane-wave and adaptive plane-wave and matched-field methods.