An analysis for scattering of scalar waves in air by a wake on the surface of water is developed. The wake on the water surface is generated as a concentrated pressure point travels over the free water surface. The wake has characteristics resembling a diffraction grating. The grating produces maximum constructive interference (resonance) in the backscattered wave under certain conditions. At resonance the scalar wavelength, water wavelength, and angle of incidence satisfy a simple geometrical condition.