On the use of ship radiated noise to determine statistical information on geoacoustic structure in shallow water

Invited paper

University of Texas, ARL:UT

Tuesday 2 june, 2015, 15:20 - 15:40

0.8 Rome (118)

Abstract:

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.