ELECTROMAGNETIC SCATTERING AND EMISSION BY OCEAN SURFACES BASED ON NEIGHBORHOOD IMPEDANCE BOUNDARY CONDITION (NIBC) WITH DENSE GRID: ACCURATE EMISSIVITY AND SENSITIVITY TO SALINITY

In order to have the required accuracies in method of moments (MoM) for numerical simulations of ocean scattering at microwave frequencies, we need to account for the much larger wavenumber of sea water relative to that of air. This paper presents simulation results of 2D ocean surface scattering with the required accuracies and that energy conservation is obeyed to 0.01%. A dense grid is required to discretize the MoM dual surface integral equation with up to 240 surface unknowns (120 surface electric field unknowns and 120 surface magnetic field unknowns) per free space wavelength. To solve the matrix equation efficiently, we develop a neighborhood impedance boundary condition (NIBC) technique to solve the matrix equation. We next calculate the emissivities of ocean surfaces using NIBC on surface integral equations using pulse basis/point matching and the Nystrom method. Results are illustrated for L-band and show that emissivities using NIBC combined with Nystrom are accurate to 2 × 10−4 for vertical polarization and 10−4 for the horizontal polarization. This means that the new method can meet the accuracy goal of 0.2 psu salinity retrieval for the NASA Aquarius mission. Results of surface fields and emissivities are also compared to that of impedance boundary condition (IBC) which requires only 10 unknowns per free space wavelength.