A two-scale scattering model for foam-free sea microwave brightness temperatures

A two-scale surface comprised of small irregularities superimposed on large undulations is defined from an empirical sea spectrum. The scattering of microwave radiation from the surface is modeled by combining geometric-optics and small-scale perturbation theory in a manner consistent with the conservation of energy. The two-scale scattering model includes multiple reflections and shadowing effects. Foam-free sea brightness temperatures are computed and show that the presence of small-scale roughness increases the brightness temperature at nadir. Comparisons with experimental data show better agreement for the two-scale model than for the geometric-optics model. Changing the small-scale perturbation parameter from 0.125 to 0.25 slightly affects the computed brightness temperatures.