Scattering of Ocean Surfaces in Microwave Remote Sensing by Numerical Solutions of Maxwell Equations
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Sea surface scattering problem is studied by Numerical Maxwell Model in 3 dimensions
(NMM3D) at L band. Compared to analytical method, numerical model does not make approximations in the modeling process and thus is more accurate. It shows that the simulation results compared well to the measurement data collected by Aquarius. On the other hand, sea water has a permittivity as large as 75 which requires dense discretization like 64 points per free space wavelength. Dense grid will cause significant numerical problems including slow convergence, large CPU and memory consumption. We propose a novel method which takes advantage of the highly lossy feature of sea water. This method relates local surface electric field to surface magnetic field within a bandwidth. Results show that the condition number of final impedance matrix is greatly reduced and is stable for different wind speeds. Utilizing steepest descent method, we are able to use coarse and dense grid for air green function and sea water green function, respectively. This has further reduced the CPU and memory cost. Finally, Negative Upwind-Crosswind (NUC) asymmetry is studied by NMM3D at L band through using two different ocean spectrum.