Measurement of the ambient noise horizontal directionality in the ocean with a circular superdirective array

Abstract

This paper describes the degree to which the horizontal directivity of the ambient noise in the ocean may be characterized using a six‐element circular superdirective array and a pressure‐gradient beamform technique. The approach used is to model the noise field as a Fourier series and to consider the array as acting like a low‐pass filter in the spatial frequency domain. The effect of the beam pattern on the noise field is calculated exactly and a method developed to remove this effect, except for bandlimiting in the spatial frequency domain. A method to reconstruct a time‐averaged representation of the noise field that is continuous in the horizontal plane even though the array used a discrete number of beams is developed. Using field data, it is shown that the magnitude and phase of the noise field coefficients may be used to make conclusions about noise mechanisms and to indicate the presence of discrete noise sources.