SCATTERING STATISTICS OF A NEGATIVELY BUOYANT THERMAL PLUME
Colosi, John A.
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Reverberation often limits effectiveness of active sonar systems due to the difficulty in discriminating between a desired target and the undesired echo returns scattered from inhomogeneities in the water column and its boundaries. An understanding of the background environment that produces the reverberation is essential for optimization of sonar systems, as it will assist in the reduction of clutter, and may also allow active systems to remotely classify the reverberation source. Many studies have dealt with the scattering properties of the boundaries and volume of the water column; however, little attention has been paid to the statistical characterization of volume scattering due to turbulence. In this thesis, laboratory measurements of high-frequency (70kHz, 120kHz, and 200kHz) narrowband acoustic backscattering through a negatively buoyant thermal plume have been performed, and the empirical echo distributions matched to statistical functions. Results show that the reverberation statistics did not always follow a Rayleigh probability distribution function (PDF), but exhibited sub-Rayleigh behavior with lighter tails, aligning more closely to a Rician PDF. A qualitative assessment of these results infers that there is a weak coherent component of the reverberation due to the temperature stratification of the thermal plume, and a strong incoherent component due to the turbulent mixing.
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