Microwave backscatter from the ocean surface away from normal incidence is often described by either the Bragg or the two-scale (composite) scattering model. In this report we study the ability of the Bragg and two-scale models to predict spatial or temporal modulation of the normalized radar cross section (&sgr;¿) caused by spatial or temporal changes in ocean surface roughness, such as those due to the presence of internal wave surface effects. Our investigation is accomplished by comparing Bragg and two-scale cross section models with cross sections calculated by a numerical electromagnetic approach. We take the numerical calculations as our standard of comparison because they are not limited by the approximations of the Bragg and two-scale models. We find that for slightly rough surfaces, the bragg model is very accurate. However, for much rougher surfaces, the two-scale model is superior and should be used for calculating both the absolute cross section and the change in cross section due to spatial or temporal modulation of the ocean wave height spectrum. The conclusions reached are relevant to interpretation of synthetic aperture radar (SAR) images of ocean internal waves collected in the SAR Internal Wave Signature Experiment (SARSEX) as well as other SAR remote sensing problems involving enhancement of ripple wavelength waves by ocean surface straining. ¿ American Geophysical Union 1989