Abstract
The received acoustic field generated by a single passage of a research vessel on the New Jersey continental shelf is employed to infer probability distributions for the parameter values representing the frequency dependence of the seabed attenuation and the source levels of the ship. The statistical inference approach employed in the analysis is a maximum entropy methodology. The average value of the error function, needed to uniquely specify a conditional posterior probability distribution, is estimated with data samples from time periods in which the ship-receiver geometry is dominated by either the stern or bow aspect. The existence of ambiguities between the source levels and the environmental parameter values motivates an attempt to partially decouple these parameter values. The main result is the demonstration that parameter values for the attenuation (α and the frequency exponent), the sediment sound speed, and the source levels can be resolved through a model space reduction technique. The results of this multi-step statistical inference developed for ship radiated noise is then tested by processing towed source data over the same bandwidth and source track to estimate continuous wave source levels that were measured independently with a reference hydrophone on the tow body.
Highlights
Inferring physical properties of the ocean from ambient noise is of interest in ocean acoustics
The idea advanced in this study is that while there are no unique methods to remove all ambiguities among RCPA, water depth, SLi, R, a, and c, the observations about Fig. 2 suggest parameter value ambiguities can be partially resolved in a meaningful manner by carefully selecting subsets of data with specific features for a multistep statistical inference approach that effectively decreases the dimensionality and volume of the hypothesis space
A numerical implementation of a theory built on a multistep maximum entropy (ME) method quantified the conditional probability distributions for a space consisting of both ocean waveguide parameters and aspect dependent source levels
Summary
Inferring physical properties of the ocean from ambient noise is of interest in ocean acoustics This manuscript focuses on analyzing ship radiated noise at Nf frequencies (fi, i 1⁄4 1, 2,..., Nf À 1, Nf) to infer statistical information on the geoacoustic properties of a seabed characterized by a sand layer in a shallow water ocean environment. From signal to noise ratio requirements in this analysis, the bandwidth of the data considered in this manuscript is 70–700 Hz. assuming that the Biot theory has at least a modicum of relevance for marine sand sediments, the analysis for this paper assumes the power law relationship given by Eq (1) with c independent of frequency; in Sec. IV E, it is assumed for 70 < f < 700 Hz that 1 < c < 3.
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