Low grazing angles (LGA) electromagnetic scattering simulation and doppler analysis of three-dimensional plunging breaker crests using the MLFMA method

The electromagnetic scattering of three-dimensional (3-D) plunging breaker wave crests at the low-grazing angles (LGA) has been numerically examined using the multilevel fast multipole algorithm(MLFMA) with adaptive higher order hierarchical Legendre basis functions. Based on the exact simulation, the plunging breaker is examined to demonstrate the “sea-spike” phenomenon which is characterized by horizontally polarization (HH) signals that exceed vertically polarization (VV) signals, especially at the grazing angles near 10°. It is strikingly different from the backscatter at moderate angles. For the evolution process of plunging waves which have a definitely measured time history corresponding to each profile, the time-dependent Doppler shifts of the backscatter is found by applying the fast Fourier transform (FFT). And its Doppler splitting and spectrum spreading have been demonstrated.