Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4297
Title: Interpreting Echo Statistics of Three Distinct Clutter Classes Measured With a Midfrequency Active Sonar: Accounting for Number of Scatterers, Scattering Statistics, and Beampattern Effects
Author: Timothy K. Stanton, Dezhang Chu, James M. Gelb, George L. Tipple, Kyungmin Baik
Publication Year: 2014
Journal: IEEE Journal of Oceanic Engineering
Volume: 99
Pages: 1-9
DOI: 10.1109/JOE.2014.2346417
Keywords: reverberation statistics,non-Rayleigh reverberation,clutter,beampattern

A newly developed formulation for echo statistics is applied to clutter data collected
with a midfrequency sonar. The physics-based formulation accounts for statistical effects from a
finite number of unresolved scatterers, each with their own arbitrary echo probability density
function (PDF) before beampattern effects, and each being randomly located in the sonar beam. In a
previous study, these data had been categorized according to whether they were associated with
bottom structures, diffuse compact clutter, and compact non-stationary (moving) clutter. The clutter
data, which are strongly non-Rayleigh, were analyzed using the K-distribution and generalized
Pareto distribution (GPD). Neither of those distributions explicitly accounts for physical effects such
as beampattern effects, although the K-distribution can be connected, for one condition, to the
number of scatterers. With this new formulation, each class of clutter is modeled, as an
approximation, as being due to an aggregation of individual scattering features, with each feature
being Rayleigh-distributed before beampattern effects. The total echo due to the beam insonifying
the aggregation is then the sum of echoes from  unresolved features within the aggregation, with
each feature randomly located in the sonar beam. The new formulation is used in a two-component
mixed PDF (mixed with a Rayleigh to account for the diffuse background) to model the statistics of
the three classes of clutter. Fits to the data reveal that bottom clutter tend to have relatively high values of , indicative of aggregates of many scattering highlights on the bottom, while compact
clutter regions tend to have smaller values of  consistent with the nature of the compact clutter
present, including discrete patches of sargassum and biologics.

Theme: Recovery, Rebuilding and Sustainability of Marine and Anadromous Species
Foci: Characterize vital rates and other demographic parameters for key species, and develop and improve methods for predicting risk and viability/sustainability from population dynamics and demographic information.