Low-frequency broadband noise correlation processing in deep-water

Abstract

The Comprehensive Nuclear-Test-Ban Treaty Organization operates an International Monitoring System (IMS). The IMS includes hydroacoustic stations composed of hydrophones deployed in the ocean deep-sound-channel in a two-kilometers-side triangular configuration(referred to as triad) in the horizontal plane. Data are continuously recorded on hydrophone triads (with a sampling frequency of 250 Hz) and have been archived during the last decade. Previous experimental studies have demonstrated that coherent waveform can be extracted from broadband coherent processing of ocean ambient noise, typically above f > 100 Hz [e.g., see Roux et al., J. Acoust. Soc. Am. 116(4), 1995–2003 (2004)] . We investigated here the emergence of coherent arrivals from the correlation processing of the low-frequency broadband ambient noise recorded during the years 2006–2007 on IMS hydrophones located in the Southern Hemisphere. This low-frequency acoustic ambient noise includes various components from anthropogenic and biological sources as well as from seismic origin (e.g., earthquakes and microseims) and also significant ice-breaking noise originating from Antarctica especially during the Austral summer period. The feasibility of passive basin scale tomography using long-term monitoring of ocean noise will be discussed.