A study of scattering of underwater sound by a rigid object near an interface is provided. The target's scattering angular pattern versus monostatic variable angles of incidence is calculated. The method used in the calculations is the boundary integral equation method (BIEM) and the target is a semi-submerged sphere which is chosen as a special case of the boundary problem in a stratiform region. An examination of scatterd echos by the rigid sphere on a free surface in pulsative incident waves is also presented. Angular distributions of sound pressure are shown and numerical results are compared with the experiments. It is observed that the calculated values agree qualitatively with experimental results.