For a simple harmonic source near the surface of the ocean, the interference pattern of direct and surface-reflected waves is described by the well-known Lloyd mirror dependence. With a pulse source, such as an underwater explosion, the interference effect is a modulation of the original pulse spectrum by a factor that depends upon frequency and the space variables. When the source and the receiving hydrophone remain at constant (though not necessarily the same) depths, both the amplitude and the period of the modulation term increase with increasing range. Depending upon the burst-receiver geometry and the reflectivity of the surface, at some frequencies the spectral energy level of the direct wave might, theoretically, be increased by as much as a factor of 4. In this paper, predicted differences between the original and the surface-modulated pulse spectrum are shown for several geometries and reflectivity coefficients, and are compared with measurements from small underwater explosions. [This work was supported by the Advanced Research Projects Agency.]