Observation of Breaking Ocean Waves with Coherent Microwave Radar

Coherent microwave radar observations with vertical polarization at 9.375 GHz are performed of breaking ocean waves in deep water (Nordsee Tower in the German Bight) and in shallow water (Jennette’s Pier, Nags Head, North Carolina) to illustrate the capability of this instrument to obtain further insight into this nonlinear, unsteady, turbulent, and multiphase process. Coherent microwave radar normally detects the phase (speed) and amplitude (energy) of the short gravity (Bragg resonant) waves (Wright, 1978). In the case of breaking waves, the line-of-sight velocity and amplitude of the backscattered electromagnetic radiation not only contain Bragg scattering contribution, but in addition specular surface scattering and volume scattering if the mixed turbulent fluid during breaking is of low enough density to approach the value in air. In this investigation some very interesting and unusual cases of wave breaking are reported with the radar observations, suggesting that radar may be the ideal instrument to observe breaking waves.

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