To model time-angle spreading from rough sediment layers, a large-scale forward-scattering approximation is applied to the correlation of the characteristic function in the expected value of the intensity. A composite distribution is derived for the transmitted and reflected portions of the acoustic wave through multiple closely spaced layers. Time spread data comparisons are used to set these composite variances at 20° on the consolidated layers and 2°–4° on unconsolidated surficial layers. These values are tested against some independent measurements of angle spreading and found to give good agreement. The model validation at low grazing angles implies that only a small number of layers are apparently participating in the scattering process at the surface of many sediments.