On the use of ship radiated noise to determine statistical information on geoacoustic structure in shallow water
University of Texas, ARL:UT
Tuesday 2 june, 2015, 15:20 - 15:40
0.8 Rome (118)
The received signals from the passage of a surface ship recorded on an array of hydrophones in shallow water can be used to infer probability distributions for values of geoacoustic parameters that represent the seabed. While there have been reports on the use of ship radiated noise for the purpose of geoacoustic inversion, very few studies have examined the problem from a statistical inference perspective. Since the source levels and the environmental parameters, such as the attenuation, have an intrinsic ambiguity, both classes of parameters must be included in the model hypothesis space H as random variables. A mathematically consistent approach that solves the statistical inference problem creates the conditional posterior probability distribution (PPD) using a maximum entropy (ME) method. The radiated noise of the R/V Knorr in the 65-650 Hz band collected in 2006 on the New Jersey continental shelf in about 70 m of water during very low wind noise conditions is used to illustrate the ME application. Conditional PPDs are constructed as a function of frequency band, frequency sampling, spatial scale of data samples, and ship aspect. As a validation of the approach, the marginal probability distribution of the geoacoustic parameters, such as the sound speed ratio and the frequency dependence of the attenuation, are used as prior information for another data sample collected along the same track, but with calibrated J-15 tonals in the 50-700 Hz band. The probability distributions of these source levels can then be compared to the measured average values and their uncertainties. One conclusion is that the inferred frequency dependence of the attenuation is consistent with a Biot theory for sandy sediments. Further, the statistics of the source levels inferred for the R/V Knorr are consistent with the International Council for Exploration of the Seas (ICES) standard for surface ship radiated noise.
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