### High-resolution B-scan bearing estimation using the fast orthogonal search

#### Abstract

A directional DIFAR passive sonobuoy has an omni-directional channel and two orthogonal directional channels. Acoustic targets can be detected on a plot of the power-spectral density of the omni-directional channel called a LOFARGRAM. In addition, a bearing estimate can be formed by the arctangent of the sine channel over the cosine channel (B-scan estimate). Traditionally, the fast-Fourier transform has been used to perform the estimate of the power-spectral density. The fast orthogonal search (FOS) algorithm has been to shown give a higher resolution spectral estimate than the FFT algorithm. The power-spectral estimate of the FOS algorithm has been used instead of the FFT in generating the LOFARGRAM and B-scan bearing estimates. It is shown in simulation and experimental data that using the FOS algorithm allows two targets, whose frequencies are spaced closer than the FFT resolution, to be resolved. By resolving two targets, two bearing estimates are calculated and the resulting estimates are much more accurate than the FFT based B-scan bearing estimates.

#### Keywords

Algorithms; Computer simulation; Fast Fourier transforms; Optical resolving power; Parameter estimation; Power spectral density; Sonoluminescence; DIFAR passive sonobuoy; Fast orthogonal search (FOS); LOFARGRAM; Omni-directional channel

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