Variability of the coherent arrivals extracted from low-frequency deep-ocean ambient noise correlations

Correlation processing of ocean noise can be used to develop totally passive ocean monitoring methods. Using various hydrophone pair orientations, this study investigates the frequency dependence, seasonal variability, and emergence rate of coherent arrivals from cross-correlations of low frequency ambient noise (f < 40 Hz) recorded on triangular hydrophones arrays. These arrays are located at five existing hydroacoustic stations of the International Monitoring System (IMS), situated in the deep-sound channel, and distributed across the Atlantic, Pacific, and Indian Ocean basins. For the majority of studied sites, persistent and fast-emerging coherent arrivals are reliably obtained if the axis connecting the selected hydrophone pair has a direct line-of-sight with regions of the globe containing stable and diffuse noise sources (e.g., polar-ice or seismic noise). Furthermore, for this favorable orientation, the emergence rate of coherent arrivals extracted between hydrophone pairs separated by long ranges (here ∼130 km) can be approximated based on measurements made between hydrophone pairs separated by short ranges (∼2 km) in the Atlantic Ocean. Hence, results from this study, obtained using existing hydrophone configurations of the IMS hydroacoustic stations, could be used to guide the placement of other hydrophone arrays over the globe for future long-range passive ocean monitoring experiments.