Feasibility of low-frequency acoustic thermometry using deep ocean ambient noise in the Atlantic, Pacific, and Indian Oceans

Abstract

Previous work has demonstrated the feasibility of passive acoustic thermometry using coherent processing of low frequency ambient noise (1–40 Hz) recorded on triangular hydrophones arrays spaced ~130 km and located in the deep sound channel. These triangular arrays are part of hydroacoustic stations of the International Monitoring System operated by the Comprehensive Nuclear Test Ban Treaty Organization (Woolfe et al., J. Acoust. Soc. Am. 134, 3983). To understand how passive thermometry could potentially be extended to ocean basin scales, we present a comprehensive study of the coherent components of low-frequency ambient noise recorded on five hydroacoustic stations located Atlantic, Pacific, and Indian Oceans. The frequency dependence and seasonal variability of the spatial coherence and directionality of the low-frequency ambient noise were systematically examined at each of the tested site locations. Overall, a dominant coherent component of the low-frequency noise was found to be caused by seasonal ice-breaking events at the poles for test sites that have line-of-sight paths to polar ice. These findings could be used to guide the placement of hydrophone arrays over the globe for future long-range passive acoustic thermometry experiments.