An analytical model for HF radar ionospheric clutter

Abstract

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 firstorder 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.

The first-order FMCW HF radar cross section model for ionosphere-ocean propagation

“…As discussed in [7] and [11], for the case of ionospheric clutter returning to the receiving antennas via the ionosphereocean propagation, the geometry is given by Fig. 1.…”

“…The development of the scattered electric field equations from the ionosphere-ocean path incorporating a general source are found in [7], [11] where the analysis has been applied to the case of a pulsed source. Here, an FMCW source is introduced into the general first-order scattered field, whose expression in frequency domain (from Eq.…”

“…Such a model could be used to predict what the reflected signals look like as a function of the oceans state including the existence of the ionospheric clutter. Walsh and Gill laid a solid theoretical foundation to describe the scattering of radio waves from the sea surface [8]- [10], and this has been extended to ionosphere clutter modelling for the pulsed radar [7], [11].…”

High frequency radar clutter power for mixed ionosphere-ocean propagation

“…The influence of the ionospheric reflection can be accounted for by a parameter referred to here as the ionosphere reflection coefficient (IRC). Applying the work in [2], [5], this paper presents three ionospheric spectral models which may be used to determine the mixed ionosphere-ocean clutter power.…”

“…This model would include the consideration of the reflection process from both the ionosphere and the sea surface. Walsh and Gill laid a solid theoretical foundation for the analysis of radio waves from the scattering sea surface [3], [4], and this been extended to ionosphere clutter modelling [2], [5]. The influence of the ionospheric reflection can be accounted for by a parameter referred to here as the ionosphere reflection coefficient (IRC).…”