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A First-Order HF Radar Cross-Section Model for Mixed-Path Ionosphere–Ocean Propagation With an FMCW Source

A theoretical model of the first-order high-frequency (HF) radar cross section (RCS) for the ionosphere-ocean propagation involving a frequency-modulated continuous wave (FMCW) source is presented in this paper. Based on previous modeling involving the scattering of HF electromagnetic radiation from the ocean surface, an expression for the first-order electric field with an FMCW source is derived for the mixed-path case in which scattering occurs from both the ionosphere and the ocean surface. Then, this field is Fourier transformed and the frequency distribution of the demodulated electric field indicates range information of the ionosphere-ocean propagation. Subsequently, the first-order RCS is developed by assuming the ocean surface and the ionosphere are stochastic processes. To investigate the power spectrum of this ionospheric-clutter mode and its relative intensity to that of the ocean clutter, a normalized ionospheric-clutter power is simulated. Numerical simulation results are first compared with that of a pulsed radar for the same ocean scattering patch. Subsequently, it is shown how the ionosphere velocities and wavelengths, and wind directions affect the power spectrum for this ionosphere-ocean propagation.