Two-point coherence of acoustic noise recorded by the North Pacific Acoustic Laboratory billboard array.

Abstract

Acoustic noise in the ocean contains extensive information about the noise sources and the propagation environment. In particular, two‐point correlation function of noise (NCCF) is known to have peaks which correspond to acoustic travel times between the two points provided the noise field is sufficiently diffuse. In this paper, measurements of acoustic noise performed during the 1998–1999 Billboard Array Experiment [Baggeroer et al., J. Acoust. Soc. Am. 117, 1643–1665 (2005)] are re‐examined with the goal of extracting environmental information. NCCF is evaluated by averaging time series of noise recorded on various vertical line arrays that comprise the Billboard Array. For any two hydrophones, NCCF is found to have a number of robust peaks. Possible generation and propagation mechanism responsible for various features of the NCCF are discussed. Statistical distributions of noise are utilized to differentiate between the NCCF peaks of different origins and to identify those peaks, which can be used to retrieve information about the sound speed without detailed knowledge of the noise sources. [Work supported by ONR.]