LINESHAPE ANALYSIS OF BREAKING-WAVE DOPPLER SPECTRA

Based on analyses of spectral densities of microwave backscatter from ocean waves, it has previously been observed that the Doppler spectra could be decomposed into different components, with Bragg scatterers r epresented by Gaussian lineshapes and faster-than-Bragg scatterers rep resented by Lorentzian and/or Voigtian lineshapes. It has been conject ured that the faster-than-Bragg scatterers are due to scattering from breaking waves, and established that the scattering mechanisms are non -Bragg in nature. In order to test the conjecture regarding the decomp osition of spectral lineshapes which represent meaningful scattering p rocesses, experiments have now been conducted at a wave tank facility. The lineshapes of breaking-wave Doppler spectra are analysed. It is f ound that for mechanically-generated breaking waves in the absence of wind, the co-polarised (HH and VV) spectra have predominantly Voigtian or Lorentzian shape and that the cross-polarised (VH and HV) spectra have exclusively Voigtian shape.