Broadband source localization using horizontal-beam acoustic intensity striations

Abstract

Waveguide invariant theory is applied to horizontal line array (HLA) beamformer output to localize moving broadband noise sources from measured acoustic intensity striation patterns. Acoustic signals emitted by ships of opportunity (merchant ships) were simultaneously recorded on a HLA and three hydrophones separated by 10 km during the RAGS03 (relationship between array gain and shelf-break fluid processes) experiment. Hough transforms are used to estimate both the waveguide invariant parameter "beta" and the ratio of source range at the closest point of approach to source speed from the observed striation patterns. Broadband (50-150-Hz) acoustic data-sets are used to demonstrate source localization capability as well as inversion capability of waveguide invariant parameter beta. Special attention is paid to bathymetric variability since the acoustic intensity striation patterns seem to be influenced by range-dependent bathymetry of the experimental area. The Hough transform method is also applied to the HLA beam-time record data and to the acoustic intensity data from three distant receivers to validate the estimation results from HLA beamformer output. Good agreement of the results from all three approaches suggests the feasibility of locating broadband noise sources and estimating waveguide invariant parameter beta in shallow waters.

Clutter depth discrimination using the wavenumber spectrum

“…Some of these methods include matched field processing which attempts to maximize an objective function which correlates the modeled and measured acoustic fields (Bucker, 1976;Baggeroer et al, 1988;Fawcett et al, 1996); modal decomposition methods which seek to match the modeled and measured modal amplitudes as a function of depth (Shang, 1985;Yang, 1987;Glattetre et al, 1989); matched mode methods which endeavor to match modeled and observed mode amplitudes as measured on a horizontal line array by use of the frequency-wavenumber (f-k) transform (Nicolas et al, 2006); and waveguide invariant approaches which are based on Chuprov's (1982) parameterization relating range and frequency to the slope of the striations in acoustic pressure in a frequency-range plot (Brekhovskikh and Lysanov, 1991;D'Spain and Kuperman, 1999). The waveguide invariant is commonly interpreted in terms of constructive and destructive interference of propagating normal modes (Turgut and Orr, 2010), but it has also been described in terms of ray theory (Gerstoft et al, 2001) and variations in eigenray arrival times (Harrison, 2011), and related to the wavenumber integration technique (Cockrell and Schmidt, 2010). Upon close inspection, the current technique can be loosely interpreted to be a dimensionally-reduced form of both the waveguide invariant process (WIP) and the mode matching method (MMM) using the f-k representation mentioned above.…”

Understanding and utilizing waveguide invariant range-frequency striations in ocean acoustic waveguides

“…(In a practical situation, one would likely plot |Υ total (ω, θ L , θ S ; w)| 2 versus snapshot number and ω while changing θ L with the snapshot number to follow the source, and then estimate the range and speed of the source. See [62]. )…”

“…The output of the beamformer will contain striations that are almost the same as the striations present in the single-hydrophone acoustic intensity, while rejecting noise coming from directions other than that of the source of interest. In [62], Turgut et al used the methods described in [66] to successfully localize an acoustic source with experimental data.…”

“…The waveguide invariant has been used for a wide range of applications such as: passive range estimation [58,56,62], matched field processing [59,23], active sonar [49,27,25], array processing [37,57,66], time-reversal mirrors [32,54,38,39], and more (See Appendix A for a complete review of the waveguide invari-ant literature). Despite its many uses, the waveguide invariant is not well studied compared to other ocean-acoustic phenomena.…”

“…• Estimating source trajectories based on range-frequency striations in an array's beamformed output [62].…”