Frequency smearing of sound forward-scattered from the ocean surface

Abstract

The results of an open sea experiment are presented in which CW acoustic signals generated by an omnidirectional source and forward-scattered by the ocean surface were measured. The statistics of the surface waves were simultaneously measured by a surface sensing buoy. It is found that for acoustic frequencies in the range of 100–500 Hz and for conditions of small surface roughness, the acoustic spectrum contains the discrete carrier frequency component with sidebands symmetrically positioned about the carrier, as predicted theoretically. The sidebands are directly related to the surface wave spectrum through a response function, which in general depends on both the acoustic carrier and surface wave frequencies. The experimental response function is compared with response functions predicted theoretically by Roderick and Cron, Parkins, and Williams. In addition, for conditions of moderate roughness, marked asymmetry in the acoustic spectra and strong spectral components that are not prominent in the surface spectra are found.