Quantitative sunglitter radiance modulations at the ocean surface due to internal waves were calculated applying a simple first order theory. The results have been compared with the image data of internal wave signatures northeast of Nantucket Shoals off the coast of Massachusetts, U.S.A., taken by the Earth Terrain Camera (ETC) during the Skylab mission. The maximum magnitudes of sunglitter radiance modulations predicted by the theory are comparable to the satellite image data. The extreme values of calculated modulations depend only weakly on the wavelength of the internal wave signature. This is consistent with the analysed ETC data. On the other hand, the shapes of simulated and measured image intensity transects across an internal wave packet are different. This may possibly be explained by the assumed idealized sinusoidal type of thermocline used in the calculations. The theory predicts that sunglint signatures of internal waves are advected relative to positions of extreme slope regions of the thermocline due to currents.