Spatial filtering in ambient noise interferometry

Carriere, O, Gerstoft P, Hodgkiss WS.  2014.  Spatial filtering in ambient noise interferometry. Journal of the Acoustical Society of America. 135:1186-1196.

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cross-correlation, emergence, field, greens-function approximation, localization, matrix, ocean, passive fathometer


Theoretically, the empirical Green's function between a pair of receivers can be extracted from the cross correlation of the received diffuse noise. The diffuse noise condition rarely is met in the ocean and directional sources may bias the Green's function. Here matrix-based spatial filters are used for removing unwanted contributions in the cross correlations. Two methods are used for solving the matrix filter design problem. First a matrix least-square problem is solved with a low-rank approximation of the pseudo-inverse, here, derived for linear and planar arrays. Second, a convex optimization approach is used to solve the design problem reformulated with ad hoc constraints. The spatial filter is applied to real-data cross correlations of elements from a linear array to attenuate the contribution of a discrete interferer. In the case of a planar array and simulated data, a spatial filter enables a passive upgoing/downgoing wavefield separation along with an efficient rejection of horizontally propagating noise. The impact of array size and frequency band on the filtered cross correlations is discussed. (C) 2014 Acoustical Society of America.