Index of content:
Volume 110, Issue 2, August 2001
- ACOUSTIC SIGNAL PROCESSING 
110(2001); http://dx.doi.org/10.1121/1.1382618View Description Hide Description
This paper presents an approach to array element localization (AEL) for towed marine seismic arrays based on regularized inversion of direct and bottom-reflected acoustic ray travel times picked from recorded seismic sections. Depth-sensor measurements at a number of points along the array are included as a priori estimates (with uncertainties) in the inversion. The smoothest array shape consistent with the acoustic data and prior estimates is determined by minimizing the array curvature or roughness. A smooth array shape is physically reasonable; in addition, minimizing curvature provides a priori information about the correlation between hydrophone positions that allows the estimation of both the offset and depth of hydrophones that record only one (or even no) acoustic arrival due to the shadowing effects of water-column refraction or reflection from arbitrary bathymetry. The AEL inversion is applied to a 102-sensor, 1.2-km towed array to correct receiver positions in the seismic velocity analysis of a seabed gas hydrate survey.
110(2001); http://dx.doi.org/10.1121/1.1381027View Description Hide Description
An algorithm is introduced for detecting signal and echo onsets and estimating their arrival times in multipath acoustic data. The algorithm accommodates superimposed narrow-band signals with continuous onsets, unknown envelopes, and arrival-time separations of less than one cycle at the dominant tonal frequency. It does not require the multipath components to be shifted and weighted replicas of each other or of a template signal. The separation of closely spaced signals is enabled by applying a prefilter that isolates spectral “tail” energy in which the onsets are discernible, and by operating on the filtered data using a matched-subspace detector that is conditioned on previously detected onsets. This algorithm has particular value for laboratory measurements, as it utilizes the high signal-to-noise ratios available in a laboratory to solve a previously intractable detection and estimation problem.