To develop a SONAR system, it is necessary to study on the scattering of acoustic waves by a seafloor. This paper includes a review of underwater acoustics and simulation results of the scattering process of acoustic waves, focused on the scattering by long-crested rough surfaces excluding the scattering by seafloor with micro-roughness. Although the wave equation with boundary conditions depicting the scattering process has been solved by using Helmholtz-Kirchhoff integral equation, the inhomogeneity of circumstances of an ocean makes it impossible to describe the wave propagation in seawater exactly. In describing the scattering of acoustic waves, an incident pulse generated from a transducer is regarded as an input signal, and all other environmental factors, related to scattering process, as a system response function. Most contents of this paper are dedicated to obtaining a numerical solution of a system response function. The major part of the solution is based on the Helmholtz-Kirchhoff integral equation, and the effects by the motion of seawater as a distribution of sound velocities in ocean and the density fluctuation of seawater. Brief experiments to confirm the simulation of the scattering of an acoustic wave have been carried out.
