A Theoretical Model of Acoustic Propagation Around a Conical Seamount
The ocean around a conical seamount is an acoustic waveguide whose depth increases linearly with range measured out from the apex, As a result of horizontal refraction, the field created by an harmonic point source in such a channel is three-dimensional in character. A full solution for this 3-D field, derived from the inhomogeneous Helmholtz equation, is discussed in this paper. The solution, giving both amplitude and phase of the field, consists of a sum of uncoupled normal modes, which are functions of the angular depth about the apex. The range and azimuthal dependence of the field is contained in the mode coefficients. These coefficients exhibit three features which are characteristic of 3-D fields in general: acoustic shadowing in the horizontal; strong spatial variations within each mode (intra-mode interference); and apparent bearing shifts in the source position, due to ray curvature in the horizontal.
KeywordsMode Coefficient Associate Legendre Function Acoustic Propagation Azimuthal Dependence Channel Angle
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