PROSPECTS FOR MEDIUM-SCALE DIFFRACTION TOMOGRAPHY ON THE SHELF

Abstract

Acoustical tomographical reconstruction of the location and sizes of spatially localized, random perturbation in a shallow-water oceanic waveguides is developed for mid-range distances. As examples of such perturbations, clouds of bubbles arising due to breaking wind waves and shoals of fishes are discussed. The ray approximation is used for the acoustical field description. The oceanic environment is presented as a medium with a background of uniformly distributed volume and surface random inhomogeneous fluctuations. Complex acoustical repetitive pulses are used as the probing signal. The receiving system consists of an array of spatially distributed hydrophones. The signals received from all hydrophones are processed on the basis of a tomographic algorithm including matched-filter processing in the spatial and frequency domains for reconstruction of the random time-delay statistical moments (average value and dispersion), which are descriptors of the observed random spatially localized inhomogeneity. As a specific model of random perturbation, a three-dimensional Gaussian cloud of fluctuations associated with parameters of a fish shoal is investigated. A vertically distributed array of receivers and a directed source of LFM-pulses are tested as the prototype of the tomographical system in a shallow waveguide with typical hydrology. Computer simulations of the tomographical reconstructions are conducted taking into account investigation of the influence of the level of additive noise on the accuracy of the reconstructed parameters.