Recent experimental results reveal acoustic penetration into sandy sediment
s at grazing angles below the critical angle. A mechanism for this subcriti
cal penetration is described based on scattering at a rough water-sediment
interface. Using perturbation theory, a numerically tractable three-dimensi
onal model is used for simulating experiments. The rough interface scatteri
ng has been treated using formally averaged methods as well as with single
rough surface realizations. Data-model comparisons show that scattering by
interface roughness is a viable hypothesis for the observed subcritical pen
etration. (C) 2000 Acoustical Society of America. [S0001-4966(00)02301-8].