ELECTROMAGNETIC SCATTERING AND DOPPLER ANALYSIS OF THREE-DIMENSIONAL BREAKING WAVE CRESTS AT LOW-GRAZING ANGLES

The electromagnetic scattering of the synthesized three-dimensional (3-D) breaking wave crests which are formed by azimuthally aligning the individual 2-D breaking wave profiles has been numerically studied at the low-grazing angles (LGA) by using the multilevel fast multipole algorithm (MLFMA) with adaptive higher order hierarchical Legendre basis functions. Different from the specular (or quasi-specular) reflection and Bragg scattering, the ``sea-spikeʹʹ phenomenon which is characterized by that horizontally polarization (HH) signals greatly exceed vertically polarization (VV) signals has been demonstrated by analyzing both the backscattering of 3-D LONGTANK series and a plunging breaker. For the time-dependent evolution of the plunging breaker, the Doppler shifts and Doppler splitting effects are investigated by applying the fast Fourier transform (FFT) with a moving Hamming window. The spectrum of HH scattering has the feature of concentration, while the spectrum of VV scattering shows the Doppler splitting effects.