A comparison of spatial spectra from a vertical line array using the maximum entropy method and the standard FFT beamformer

Abstract

Acoustic data were collected in the Northeast Pacific using a vertical line array placed near the bottom. Narrow‐band data were provided by a cw source (54 Hz) which was towed at a nominal depth of 91 m radially away from the array. Time series from each hydrophone were converted to the frequency domain using an FFT with an 0.625‐Hz processing band. Spatial spectra were obtained for the source frequency using both a standard FFT beamformer and the maximum entropy method (MEM), which was implemented using the Burg algorithm in complex form. Conventional power averaging was utilized for the standard FFT beamformer while the MEM beamformer displayed the best results when the averaging was performed over the filter coefficients. The MEM beamformer was exercised for different model orders, with the sharpness of the signal arrivals increasing with increasing model order as expected. The half‐power width of typical signal arrivals was approximately seven times smaller with the MEM beamformer than with the standa...