An analytical model for HF radar ionospheric clutter

In this paper, an analytic model for the mixed path mode of ionospheric clutter associated with high frequency surface wave radars (HFSWR) operating in an ocean environment 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 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 ionosphere clutter is developed. 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 40-50 dB. Further, it is spread over several Hertz in Doppler, depending on ionosphere horizontal velocity and reflecting path non-uniformity. Also, this component can be present from a certain minimum range, depending on ionosphere virtual height, out to the maximum radar range.