Spectral structures and radiation patterns of scattering waves in a layered acoustic half-space

 Scattering waves in a layered acoustic half-space are analyzed in terms of their spectra, which are sets of wavenumbers for which proper and improper eigenfunctions for a layered wave field can be observed. The scattering waves are caused by the interaction between an incident plane wave and a low acoustic-velocity area. The boundary-integral equations and the spectral form of Green's function developed by the author are introduced into the analysis. The waves are decomposed into their spectra by interchanging the boundary integral and spectral integral or summation for the Green's function. The spectral amplitudes and radiation patterns of the scattering waves are investigated for different frequencies, based on numerical calculations. According to the numerical results, the scattering waves consist mainly of components of continuous spectrum. In addition, the scattering waves show strong directionality and exhibit a tendency to propagate in the forward direction as the frequency increases.