The convergence and divergence of ocean current can modify the spectral of surface waves and this modification varies with the wave propagation speed which is a function of wavelength. Over Keelung Sill north of Taiwan, the mostly-semidiurnal tidal current creates a horizontal divergence condition as it approaches and speeds up towards the shallow sill, and a convergence condition at downstream of the sill. For waves propagating upstream towards the sill, its ground speed decreases, like a wave approaching the beach, the wave amplitude increases till the wave breaks and loses its energy, and the remaining energy is reflected back. On the upstream side, the influences of current on waves are the opposite, and all waves that propagate upstream and pass over the sill will be stretched out and result an unusually smooth surface. Aerial photographs from UAV, both fixed-win model airplane and kite, and in situ measurement of surface wave spectra were analyzed to study the spatial distribution of surface roughness and the wave spectra, and the influence of ocean current on surface waves of different wavelength.