| Abstract: | To study the Doppler (DP) spectrum of a flying target above the dynamic oceanic surface, a two-level quasi-stationary algorithm (TLQSA) of the finite element method (FEM) with domain decomposition (DDM) is developed. The DP spectrum of a fast-moving target requires a small time-sampling rate. At most time steps, scattering from the flying target is solved by the FEM solution in only one sub-domain; meanwhile the interactions between the target and rough sea surface in other sub-domains are obtained by solving the global DDM coupling matrices. The slowly moving sea surface is evolved at a larger time step and the DP of oceanic clutter is obtained through all-subdomain FEM calculation. Numerical simulations of the DP spectrum from a target flying above the dynamic oceanic surface with and without a ship presence are obtained. The functional dependence of the DP spectrum in both the time and frequency domains upon the sea surface wind speed, target altitude, observation angle etc. are demon- strated and discussed. |
