Tue16Oct20184:00 pmLewis Hall 101
Colloquium: Ocean Remote Sensing Using Passive Acoustics
George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Ocean Remote Sensing Using Passive Acoustics
Acoustic waves carry information about their environment as they propagate, especially in the ocean which can conduct sound very efficiently over significant distances. Hence underwater acoustic waves can be exploited for a wide variety of ocean remote sensing activities. Modern acoustic remote sensing involves receiver arrays and array signal processing to recover multidimensional results, for instance the characterization of medium inhomogeneities due to sound speed fluctuations or discrete sound scatters. On one hand receiver arrays are becoming increasingly autonomous, miniaturized and capable of long term deployment thus enabling the practical use of acoustics for ocean remote sensing applications. However, on the other hand, conventional acoustic remote sensing techniques still typically rely on controlled active sources which can be problematic to deploy and operate over the long term, especially if multiple sources are required to fully illuminate the ocean region of interest. To address this crucial limitation, totally passive versions-i.e. using only receiver arrays- of existing remote sensing techniques can be developed by taking advantage of uncooperative sources of opportunity (e.g. shipping noise) or the ubiquitous ocean ambient noise which have not typically been used in traditional ocean sensing applications due to their apparent complex nature. This fully passive approach can also be advantageous when regulations forbid the use of active sound sources to prevent the disruption of natural animal activities or when no active sources are readily available-e.g. at very low frequencies (~10Hz) or during covert operations. This presentation will discuss recent development of ocean remote sensing using passive acoustics notably 1) Passive acoustic thermometry to estimate deep ocean temperatures variations using coherent processing of low-frequency ambient noise, 2) Localization of drifting sensor networks using ambient noise to enable random volumetric ad-hoc receiver array for tracking underwater targets; and 3) Monitoring of shallow water sound channel using shipping sources of opportunity. Additionally the extension of these passive remote sensing techniques to seismic and structural health monitoring applications will also be presented.