On the Development of a High-Frequency Radar Cross Section Model for Mixed Path Ionosphere-Ocean Propagation

An analytic high-frequency (HF) radar cross section model for ionosphere-ocean propagation is presented. Based on earlier work, an expression for the first-order received electric field after a single scatter from each of the ionosphere and sea surface is derived and reduced to integral form. The field integrals are taken to the time domain, with the source field being that of a vertically polarized pulsed dipole antenna. Subsequently, the first-order radar cross section for the mixed path mode of ionospheric clutter is developed. The ionosphere reflection coefficient used in the analysis is assumed to be a stochastic process with an associated spectral density function to account for phase variations along the surface associated with nonuniformity of the signal path. Simulation results for the new cross section are also provided. It is shown numerically that the expected magnitude of the ionosphere clutter, under reasonable assumptions, exceeds the dominant first-order ocean clutter for the same apparent range by 50-60 dB. Further, it is spread in Doppler, depending on the ionosphere horizontal velocity and reflecting path nonuniformity. Also, this component can be presented from a certain minimum range, depending on ionosphere virtual height, to the maximum radar range.