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 represented by Gaussian lineshapes and faster-than-Bragg scatterers represented by Lorentzian and/or Voigtian lineshapes. It has been conjectured 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 decomposition of spectral lineshapes which represent meaningful scattering processes, experiments have now been conducted at a wave tank facility. The lineshapes of breaking-wave Doppler spectra are analysed. It is found 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