A unified model for reverberation and submerged object scattering in a stratified ocean waveguide

A unified model for reverberation and submerged target scattering in a stra tified medium is developed from wave theory. The advantage of the unified a pproach is that it enables quantitative predictions to be made of the targe t-echo-to-reverberation ratio in an ocean waveguide. Analytic expressions a re derived for both deterministic and stochastic scattering from the seaflo or and subseafloor. Asymptotic techniques are used to derive expressions fo r the scattering of broadband waveforms from distant objects or surfaces. E xpressions are then obtained for the scattered field after beamforming with a horizontal line array. The model is applied to problems of active detect ion in shallow water. Sample calculations for narrowband signals indicate t hat the detection of submerged target echoes above diffuse seafloor reverbe ration is highly dependent upon water column and sediment stratification as well as array aperture, source, receiver, and target locations, in additio n to the scattering properties of the target and seafloor. The model is als o applied to determine the conditions necessary for echo returns from discr ete geomorphologic features of the seafloor and subseafloor to stand promin ently above diffuse seafloor reverberation. This has great relevance to the geologic clutter problem encountered by active sonar systems operating in shallow water, as well as to the remote sensing of underwater geomorphology . (C) 2001 Acoustical Society of America.