HR: 17:30h
AN: S34B-07 INVITED     [Abstracts]
TI: Emergence of the time domain Green's function from ocean noise correlations.
AU: * Sabra, K
EM: ksabra@mpl.ucsd.edu
AF: Marine Physical Lab. Scripps Inst. Ocean. UCSD, 9500 Gilman Drive, La Jolla, 92093-0238
AU: Roux, P
EM: proux@ucsd.edu
AF: Marine Physical Lab. Scripps Inst. Ocean. UCSD, 9500 Gilman Drive, La Jolla, 92093-0238
AU: Gerstoft, P
EM: gerstoft@ucsd.edu
AF: Marine Physical Lab. Scripps Inst. Ocean. UCSD, 9500 Gilman Drive, La Jolla, 92093-0238
AU: Kuperman, W
EM: wak@mpl.ucsd.edu
AF: Marine Physical Lab. Scripps Inst. Ocean. UCSD, 9500 Gilman Drive, La Jolla, 92093-0238
AU: Fehler, M
EM: fehler@lanl.gov
AF: Los Alamos National Laboratory, P. O. Box 1663, MS D443 Bldg 1572 Room 108, Los Alamos, NM 87545
AB: Coherent deterministic arrival-times can be extracted from the derivative of the time-averaged ambient noise cross-correlation function between two receivers. These coherent arrival-times are related to those of the time domain Green's function (TDGF) between these two receivers and have been observed experimentally in various areas (e.g. in ultrasonics, seismology or underwater acoustics). We will review theoretical and experimental results obtained using this technique with ocean noise recordings [Roux et al., J. Acoust. Soc. Am. 115, (2004)]. The non-intuitive relationship between the TDGF and the noise cross-correlation function can be explained based on a simple time-domain image formulation of the noise cross-correlation function, for a uniform distribution of noise sources in a waveguide [Sabra et al., J. Acoust. Soc. Am. 117, (2005)]. The deterministic multipath TDGF appears through spatial and temporal integration over the distributed random noise sources in the ocean and corresponds to correlation of random noise passing through both receivers. We will present an analysis of the convergence time of this correlation process. We will investigate how, for a given environment, the emergence of the TDGF depends on the spatial and temporal noise distribution, the correlation window length, and the frequency bandwidth. Experimental results using long time noise recordings that were collected in May 1995 near the South California coast at an average depth of 21m show that time delays between the elements of a bottom hydrophone array can be estimated with good precision [Sabra et al., IEEE J. Ocean Eng. (2005)]. These coherent wavefront arrivals across the array's aperture are used for array element self-localization and self-synchronization. Environment fluctuations, typically present in the ocean, are an important limitation for the averaging time required by this noise cross-correlation technique. But this is not the case in seismology where years of noise recordings are available on broadband seismometers networks in an (almost) invariant environment. Applications of the presented results to seismology will be discussed.
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere (1236)
SC: Seismology [S]
MN: Fall Meeting 2005