Acoustic scattering from a structure placed in a bounded medium
Given a harmonic source producing an acoustic field incident on a structure placed in a range independent shallow water environment, an algorithm is developed to compute the scattered field from a scatterer that is rigid, soft or an elastic shell. The method of superposition is applied where the scattered field is approximated to be equivalent to the field produced by a large number of point sources placed on a surface inside the scatterer. The source strengths are determined by imposing boundary conditions on the surface of the scatterer. This algorithm is applicable even when the source or the receiver is close to the scatterer as well as in the case where the scatterer is close to the surface. To test the algorithm, scattering computations are made for a cylinder with hemispherical end-caps in an isovelocity fluid with soft boundary conditions on top and rigid boundary conditions on the bottom and compared to the scattered field computed by using an algorithm discussed by Ingenito [F. Ingenito, J. Acoust. Soc. Am. 82, 2051-59(1987)] where approximations are made for the case when both the source and the receiver are distant from the scatterer and when the scatterer is distant from the surface. Results from both methods agree in the range of applicability of Ingenito's method. In addition, scattering computations are made in the frequency domain and the time domain of rigid, soft and elastic structures placed in a medium where the speed of sound is depth dependent. Finally, an algorithm is developed to extract the free field response of a scatterer from measurements made in shallow water over long ranges using horizontal or vertical arrays of sources and receivers.