Directional Distribution of Ambient Noise in the Ocean

Abstract

The directional distribution of ambient noise in the ocean has not been measured previously. The conventional, trainable, searchlight transducer is unsuitable for measurements; observations in several directions in succession are inadequate owing to the required assumption of a stationary process. In addition, the single transducer fails to permit investigation of the correlation of envelope fluctuations in several directions. Accordingly, the system employed is based upon a 32-element receiving array employing 32 beams, simultaneously distributed uniformly over all space [V. C. Anderson, J. Acoust. Soc. Am. 30, 470 (1958)]. The signal reception and processing system is described briefly. Because of the finite beam widths (low resolving power) and beam side lobe structure, an analysis technique converting observed relative beam responses to the true field distribution has been developed. Data obtained at depths to 1000 ft are discussed in light of departures of ambient noise from an isotropic distribution. Preliminary deductions concerning the sources of sea ambient noise found in the distribution are presented. (This work represents one of the results of research carried out under contract with the Office of Naval Research.)