Shallow Water Beamformer

Spatial processing for Navy arrays has been designed in nearly all cases based on the a horizontally propagating plane wave model, the underlying assumption being that energy arrives from far field targets as a superposition of free field traveling waves at frequencies determined by the target signature. For most situations this model has been considered "good enough", particularly in deep water operations. Multi-path, has been ignored in spatial processing and dealt with in various ad hoc ways for target localization. It is well known that acoustic propagation is much more complex than the simple model due to boundary interactions (as evidenced by multi-path), sound velocity variability, and other more complicated effects. These effects are most prominent in shallow water and at low frequencies where surface and bottom interactions are prevalent. Shallow water environment presents the technical challenge of designing beamformers based on a suitable shallow water signal model rather than the simple horizontal plane wave assumption. Our proposal is to design such a beamformer based on state-of-the-practice characterization of shallow water sound fields. We will focus our efforts first on horizontal line arrays (design will be extendable to volumetric arrays), and surface noise sources (ships and surf hot spots).