Fluctuation-based beamformer for the enhancement of low-fluctuation amplitude signals

Abstract

A formulation of the cross-spectral density matrix (CSDM, also known as the data covariance matrix) is presented, which is sensitive to the fluctuations that occur naturally in undersea acoustic data. This new formulation, called the AWSUMk cross-spectral density matrix or AkCSDM, is patterned after the WISPR and AWSUM filters, both of which are sensitive to amplitude fluctuations. The AkCSDM utilizes a similar approach to achieving sensitivity to fluctuations, but AkCSDM goes a step further by including sensitivity to phase fluctuations as well as amplitude fluctuations. The formulation is described and results are presented for beamforming the elements of a towed horizontal line array. The results indicate that in the case of a low-fluctuation amplitude tonal, the signal-to-noise-ratio of the AkCSDM beamformer is much greater than the conventional CSDM beamformer, and that in some cases the noise and clutter signals were nearly eliminated. Such results suggest that ‘‘noise elimination’’ is a better description of the AkCSDM beamformer than is ‘‘noise suppression.’’ [Work supported by ONR and NRL.]