Linear array beamforming in harbor environments.

Abstract

The use of linear arrays of sources to focus low‐frequency sound on a target zone of limited spatial extent in a very shallow water environment is a topic of current interest for applications such as harbor defense. While linear array beamforming provides a starting point, the analytical expressions for beam response of a line array found in standard acoustics texts are developed for arrays of compact simple sources in a free‐field environment. In contrast, the typical harbor environment is characterized by very shallow water depths, varying bottom conditions, irregular vertical boundaries, and the presence of multiple scattering bodies. In addition to environmental conditions, the size and cost of low‐ frequency sources limit the validity of the simple source assumption and impose practical limits on the number of sources and maximum aperture length. Standard beamforming calculations are compared to measured data from a June 2008 harbor acoustic propagation experiment to quantify limitations of the linear array theory in estimating the beam response and three‐dimensional sound field generated by an array of a small number of noncompact low‐frequency sound sources in a real harbor environment. The relative impacts of environmental factors and source characteristics are also discussed.