In the frequency region below 1 kc, the effect of velocity inhomogeneities on acoustic propagation in the ocean will be negligible. In this frequency region, fluctuations in travel time and ray direction will be caused by scattering from rough boundaries. In this paper, the effect of boundary scattering on the resolution of ray paths is investigated. Using a simplified model of the process, a rough estimate of the spatial line broadening of a low‐frequency ray in the ocean is obtained.