A Novel approach to bottom scattering using a narrow acoustic beam

The acoustic response of the ocean bottom to a probing pulse is a complex and complicated process. This process is influenced by with the form of an acoustic transmitting/receiving beam and by the physical processes involved in sound scattering from the surface and the volume of the ocean bottom. The complexities of these phenomena often obscure an intuitive understanding of the underlying principles of echo formation and its reception. In this paper, we propose a simplistic model for this complex process using filter theory. The bottom is represented as a surface reflector with an acoustic wave front sweeping over it with time-varying velocity. The impulse response of a smooth flat bottom is characteristic of a low pass-filter that will greatly attenuate the impinging high frequency pulse. On the other hand, bottom undulations will modulate the reflected signal such that it can be represented by the impulse response of a band-pass filter. The received echo can be represented as the response of such filter to a high frequency pulse. The characteristics and amplitude of the echo are dependent on frequency spectrum overlap between the transmitted pulse spectrum and the filter frequency response. In the paper, we discuss several cases of interest with the intent to provide a solid intuitive understanding of the echo formation from the system point of view.