Vector sensors and vector sensor line arrays: Comments on optimal array gain and detection

This paper examines array gain and detection performance of single vector sensors and vector sensor line arrays, with focus on the impact of nonacoustic self noise and finite spatial coherence of the noise between the vector sensor components. Analytical results based on maximizing the directivity index show that the particle motion channels should always be included in the processing for optimal detection, regardless of self noise level, as long as the self noise levels are taken into account. The vector properties of acoustic intensity can be used to estimate the levels of nonacoustic noise in ocean measurements. Application of conventional, minimum variance distortionless response, and white-noise-constrained adaptive beamforming methods with ocean acoustic data collected by a single vector sensor illustrate an increase in spatial resolution but a corresponding decrease in beamformer output with increasing beamformer adaptivity. Expressions for the spatial coherence of all pairs of vector sensor components in homogeneous, isotropic noise show that significant coherence exists at half-wavelength spacing between particle motion components. For angular intervals about broadside, an equal spacing of about one wavelength for all components provides maximum directivity index, whereas each of the component spacings should be different to optimize the directivity index for angular intervals about endfire.