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Recent years have seen the development of robust and efficient numerical techniques for exact calculations of rough surface scattering. We discuss how such methods, typically formulated for time-independent surfaces, can be extended to calculate scattering from time-evolving ocean-like surfaces. Estimates are provided for the choice of parameters in such time-varying simulations. The method of ordered multiple interactions (MOMI) is used to calculate time-varying scattering from surfaces generated according to linear and nonlinear (Creamer) models for incidence angles ranging from normal to low grazing. We discuss the runtime considerations and demonstrate that combining the MOMI with a fast multipole method (FMM)-type acceleration technique makes large-scale time-varying Monte Carlo simulations possible. The average Doppler spectra of backscattered signals obtained from such simulations are compared for different incident angles, polarizations, and surface models. In particular, the simulations show a broadening of the Doppler spectra for nonlinear surfaces, especially at low grazing angles (LGA) and a separation of the vertical and horizontal polarization spectra at LGA for nonlinear surfaces. This spectral separation at LGA is not observed when the linear surfaces are used.Index Terms-Doppler spectrum, electromagnetic scattering by rough surfaces, low grazing angles, magnetic field integral equation, numerical methods, Pierson-Moskowitz spectrum.

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The results of a study to determine the correlation of the surface scattering cross section per unit area at normal incidence σ°(0°) and 13.9 GHz with surface wind speed are presented. Comparing σ°(0°) measurements with ship reports of wind speed, it was found that an algorithm could be devised which is capable of producing wind speed estimates from σ°(0°) measurements to a precision of 2.6 m/s for winds in the range of 1–21 m/s. Correlations with buoy measurements in the range of 1–10 m/s show an rms precision of 2.1 m/s with the possibility of a slight bias in the ship report based algorithm. A study of σ°(0°)‐inferred wind speeds in relation to hindcast estimates shows a distinct tendency in the hindcast results to be biased toward the low side in the absence of sufficient ship reports of wind and pressure. The results of this study indicate that a short‐pulse radar altimeter can provide reasonably accurate estimates of surface wind speeds over a rather large range of wind speeds.