Measurement of Capillary Oscillations of the Sea Surface

Capillary waves on the sea surface strongly influence scattering of both optical and microwave radiation. Although the amplitude of capillary waves is fractions of a millimeter, the slopes formed on capillary waves often exceed 30°, which leads to a strong change in the effective reflection coefficient, absorption, and backscattering cross section. Capillary waves are studied in detail in pools, but they have not been measured in natural marine conditions. In this paper, a remote method for measuring slopes, amplitude, direction of the wave vector, and structure of capillary waves in natural conditions is proposed. The method is based on recording the distortion of laser beams incident from top to bottom on the sea surface with a video camera. The authors managed to solve the inverse problem of calculating all the parameters of a capillary wave based on the shape of a capillary lattice in video frames. The sensitivity of the method for measuring the wave amplitude is 30 µm at a distance to the surface of over 4 m.