Sonar Performance Estimation Model with Seismo-Acoustic Effects on Underwater Sound Propagation.

摘要

Correct estimation of the performance of any sonar system depends on accurate computation of the propagation loss of the signal. In underwater acoustics, low-frequency sound is less attenuated and the easiest signal to detect at large distances. The theory of normal modes has thus been modified to incorporate the effects of shear waves from the elastic ocean floor. Effects of absorption have also been included as the imaginary component of the shear and compressional wave numbers. The eigenvalues of the multilayered wave guide are searched in the complex K-plane by the Levenberg-Marquardt minimization of the magnitude of the complex characteristic equation. The liquid layers of the water column are represented by a linear wave number squared with depth to better simulate the sound speed profile. It has been found that the compressional sound speed of an elastic layer can also have a linear wave number squared and that the density in a liquid layer can be a variable with depth and still obtain solve wave equations. A semi-infinite elastic bottom basement layer with compressional and shear absorption has been included to the normal mode model and been found that the absorption causes the wave number spectrum of the radiating modes to be inherently discrete, hence the number of radiating modes are drastically reduced. Range dependence of the acoustic properties and the boundaries of the ocean have been induced by a modified version of the adiabatic normal mode theory. This newly developed version handles the shear wave contribution and the fact that the eigenvalues and depth functions are complex. Keywords: Elastic ocean bottom; Propagation loss. (EDC)