Physical processes of microwave backscattering from laboratory wind-wave surfaces

Microwave backscattering from wind-wave surfaces in a wind-wave tank is investigated by using an X-band (9.6 GHz) scatterometer. The radar beam is focused on the water surface by using an ellipsoidal antenna to clarify phase relationships between the backscattered signature and the wind-wave surfaces. At a slant incidence angle (45° upwind), the backscattered intensity and the Doppler velocity are in phase with the surface displacement. High Doppler velocity observed at the crests of the individual waves coincides with the propagating speed of the crests. It is concluded that the fine structures of wind-wave surfaces, which are trapped near the crests and are propagating with the crests, are main contributor to the microwave backscattering