Numerical study of wide-band low-grazing HF clutter from ocean-like surfaces

Backscattering of a vertically polarized, ultra-wide band HF pulse (3-30 MHz) from one-dimensional Pierson-Moskowitz impedance surfaces is studied using method of moments (MoM)-based numerical simulations. With the field source located near the surface, low-gazing regime is realized for the most of the illuminated region. The direct numerical solution is compared to approximate calculations based on the small perturbation method (SPM). Once the Norton surface wave effects are included in the SPM scattering coefficient, average clutter levels as well as waveform shapes generally show good agreement. As the sea state increases, backscatter returns from farther ranges exhibit larger discrepancies. In such a situation, using the "effective surface impedance" (that accounts for surface roughness) brings SPM-based average clutter levels in agreement with their MoM counterparts: however, the differences in waveform shapes persist. Future studies will use the simulation capability described in this paper to investigate the ability of a short-pulse, ultrawideband HF radar to image ocean waves, measure surface currents and surface current shear, and detect targets.