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Acoustic interferometry for geoacoustic characterization in a soft-layered sediment environment
Ren, Q.; Hermand, J.-P. (2013). Acoustic interferometry for geoacoustic characterization in a soft-layered sediment environment. J. Acoust. Soc. Am. 133(1): 82-93. hdl.handle.net/10.1121/1.4768879
In: The Journal of the Acoustical Society of America. American Institute of Physics: New York, etc. ISSN 0001-4966, more
Peer reviewed article  

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Keyword
    Marine
Author keywords
    acoustic signal processing, acoustic wave interferometry, acoustic wave velocity, clay, discharges (electric), geophysical signal processing, oceanographic regions, oceanographic techniques, sediments, underwater sound

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Abstract
    The broadband spectrogram of a moving surface ship usually exhibits striations. Their structure is determined by bottom conditions of the shallow water waveguide and can therefore be used for environmental characterization. A two-step acoustic interferometry technique is proposed to estimate main geoacoustic properties of unconsolidated sediment by exploiting local features of the striations. Their positions at low frequencies are first used to detect the changes in sediment properties with respect to a reference sediment and provide a reliable estimation of the changes through the determination of a frequency shift. Then toward higher frequencies, local frequency-range areas with salient striations are selected to refine the solution with their structure features. The technique is tested with passive acoustic ship run data collected southeast of the island of Elba in the Mediterranean Sea in 2007. Data from the four receivers of a shallow sparse vertical array are processed to estimate the thickness and compression wave speed of a soft clay layer overlying a harder bottom. The results from individual receivers are close and agree well with active inversion results and seismic profiles in the same area. Moreover, a better resolution is obtained by combining these results. This method is demonstrated to be robust to source range uncertainties due to the striation stability to its small variation. The good experimental results suggest the technique is an effective tool for mapping the geoacoustic properties of wide coastal areas with easily deployed receiver systems or even one single receiver.

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