The frequency spreading of a monochromatic acoustic plane wave reradiated by the moving, rough surface of the ocean is described using the spectral density of the far‐zone reradiated pressure. This pressure is calculated using the method of physical optics for a surface assumed to be described by the Neumann‐Pierson directional wave spectrum. The results are specialized for the cases of slightly rough and very rough wind‐generated seas. For the slightly rough case, the spectral density contains a specularly reflected component at the frequency of the incident radiation and two monochromatic scattered components that are Doppler‐shifted by equal amounts from the frequency of the incident radiation. The magnitude of the deviation of each of the Doppler‐shifted frequencies is the same and depends on the angles of incidence and observation relative to the wind direction and also on the incident frequency. For the very rough surface case, the spectral density of the far‐zone reradiated pressure is of Gaussian form. In the specular direction, the center of the spectrum is at the frequency of incident radiation but is shifted away from that frequency for other angles of observation with a shift proportional to wind speed. The width of the spectrum increases as the three‐halves power of the wind speed and also depends upon the geometry.