Exploiting the Spatio-Temporal Coherence of Ocean Ambient Noise for Passive Tomography

• Main Author: Sabra, Karim G
• Other Authors: GEORGIA INST OF TECH ATLANTA SCHOOL OF MECHANICAL ENGINEERING
• Format: Text
• Language: English
• Published: 2012
• Subjects: Physical and Dynamic Oceanography; Acoustics; *AMBIENT NOISE; *TOMOGRAPHY; *UNDERWATER ACOUSTICS; ACOUSTIC ARRAYS; ACOUSTIC DETECTION; ACOUSTIC FIELDS; ANTARCTIC REGIONS; BEAM FORMING; COHERENCE; GREENS FUNCTIONS; HYDROPHONES; INDIAN OCEAN; LOW FREQUENCY; TIME DOMAIN; WAVEFRONTS; IMS(INTERNATIONAL MONITORING SYSTEM); CTBTO(COMPREHENSIVE NUCLEAR-TEST-BAN TREATY ORGANIZATION); AVERAGED CROSS-CORRELATION WAVEFORMS; Antarctic; Indian; Antarc*
• Online Access: http://www.dtic.mil/docs/citations/ADA575085; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA575085

The long-term goal is to develop passive modalities of acoustic ocean monitoring techniques such as acoustic tomography or acoustic thermometry using Cross-correlation processing of ocean ambient noise. Extracting the coherent component of the ambient noise field propagating between a pair of passive receivers provides a means for passive acoustic sensing of the ocean environment. For instance, the arrival-times structure of the ambient noise cross-correlation time-function between a pair of receivers can yield an estimate of the arrival structure (or wavefronts) of the actual time-domain Green s function between these receivers, as if one of the passive receiver acted as an active source. Hence cross-correlation processing of ocean ambient noise has been suggested as a potential means for developing noise-based (or passive) modalities of acoustic ocean monitoring techniques such as acoustic tomography or acoustic thermometry The main objective of this year research was to demonstrate that coherent arrivals can indeed be extracted from cross-correlations of very-low frequency ocean ambient noise (1 Hz f 20 Hz) between pairs of hydrophones of the same hydroacoustic station located in the SOFAR channel of the Indian Ocean. The emergence rate of these coherent arrivals was determined in order to assess the feasibility of ocean basin scale (i.e. long range) passive tomography. The original document contains color images.