Time-warping in underwater acoustic waveguides
Michael G. Brown
Abstract
The traditional way to isolate fixed mode number contributions to a transient wavefield in an underwater acoustic waveguide involves measuring the wavefield on a dense water-column-spanning vertical array and exploiting orthogonality over depth of the modes at each frequency. Recently it has been demonstrated that essentially the same goal can be accomplished in an ideal shallow water waveguide using measurements made on an isolated receiver by employing a signal processing technique known as time-warping. Time-warping makes use of a special nonuniform temporal sampling of the measured signal for which contributions from individual mode numbers are isolated in the frequency spectrum of the time-warped signal. The time-warping transformation in a general underwater acoustic waveguide is derived here. The general time-warping transformation is shown to reduce to the ideal shallow water waveguide time-warping transform as a special case. Use of the general time-warping transformation is illustrated with simulations in both a mid-latitude deep ocean environment and a high-latitude environment.