In this paper, we study backscattering from the ocean using 3D numerical simulation of Maxwell's equation (NMM3D). Previously we used NMM3D to compute backscattering and emissivity of rough soil surfaces for active and passive microwave remote sensing of soil moisture [1, 2] at L, C, X and Ku bands. The computed results were in excellent agreement with measurement data for co- and cross-polarizations. The results include multiple incident angles and various soil moisture conditions. NMM3D was also combined with distorted Born approximation to vegetated surface to give tabulated backscatter lookup table for soil moisture retrieval globally in NASA SMAP mission. In calculating soil surface scattering, Poggio-Miller-Chan-Harrington-Wu-Tsai (PMCHWT) formulation for dielectric surfaces and Rao-Wilton-Glisson (RWG) basis functions are used to obtain accurate results.