This work is focused on the effects of large-scale wind-generated gravity waves on scatterometer wind-measurement accuracy. We present theoretical and experimental evidence of the important role played by the degree of wind-wave coupling in surface geometry and therefore in microwave signatures. Seasat scatterometer wind-measurement errors are analysed, and an error bias is found to be related to the degree of wind-wave development. Attention is focused on a dynamic measure of wind-wave development that characterizes the rate of energy transfer from the mean wind to the energy-carrying portion of the wave spectrum. An explanation of the bias is suggested based on the consideration of an additional component of surface scattering caused by electromagnetic-wave diffraction at the crests of individual, sufficiently steep wavelets.