Numerical studies of low grazing angle backscatter from 1D and 2D impedance surfaces

Numerical simulations of near grazing angle backscattered fields from ocean-like impedance surfaces are described. Both one dimensional and two dimensional surfaces are considered, and efficient algorithms are applied to allow simulations for the large surface sizes required in the near grazing angle region. The algorithms used are based on Monte Carlo simulation using either the sparse matrix-flat surface iterative approach with canonical grid (SMFSIA/CAG) or a recent improved forward-backward technique which allows larger surface heights to be considered. Backscattering cross sections are illustrated for linear hydrodynamic surfaces described by a Pierson Moskowitz spectrum at grazing angles from 1 to 10 degrees in the one dimensional case, and at 10 degrees in the two dimensional case. Variations with surface spectrum low frequency cutoff are investigated, and demonstrate that improved hydrodynamic models for the ocean surface are required to observe “sea-spike” behaviors at low grazing angles