Wave effect on microwave scattering at water surface

Microwave scattering at the water surface where a water surface wave coexisted with wind-waves was measured in an experimental water tank. Scattering characteristics, scattering coefficients and Doppler spectra of backscattering microwaves and the relation between scattering characteristics and physical properties of a water surface wave such as wave length, wave height, wave phase and orbital velocity have been investigated. The tilt modulation by water surface slope and the change of wind velocity near water surface by the fluctuation of water surface level were confirmed as influence of water surface wave in microwave backscattering strength. However, the hydrodynamic modulation could not be confirmed. The influence of a water surface wave in microwave backscattering had a strong showing at the Doppler spectrum of backscattering microwave. At first, the middle frequency of the Doppler spectrum of backscattering microwave from the water surface where a water surface wave coexisted with wind-waves was corresponding to that of the wind-wave water surface generated only by wind in the same incident angle and azimuth. The band width of the Doppler spectrum was the value that added 2 times of orbital velocity of water surface wave to that of the wind-wave water surface. The influence of azimuth to the band width was not shown