USE OF THE WIGNER-VILLE DISTRIBUTION TO COMPENSATE FOR IONOSPHERIC LAYER MOVEMENT IN HIGH-FREQUENCY SKY-WAVE RADAR SYSTEMS

High-frequency (HF) sky-wave radar signals propagate to and from the target by means of the ionosphcre. The difficulty in obtaining very narrow beamwidths at HF, and the long ranges involved, mean that the signal backscattered from the ground is often several orders of magnitude greater than the target echo. To resolve the target, coherent signal processing techniques are necessary, detecting the target echo by virtue of the Doppler shift caused by the target's radial velocity. Unfortunately, movement of the ionospheric layer by which the radar signal has propagated often causes the clutter spectrum and target to spread in the frequency domain, rendering extended coherent integration pointless. The movement of the ionosphere can be regarded as producing frequency modulation of the radar signal, and thus if this modulation can be estimated the radar signal may be corrected for the ionospheric contamination. A technique using the complex argument of the first-order moment of the Wigner-Ville distribution of the filtered radar echo is proposed as a means of estimating the ionospheric frequency contamination, and a correction technique is discussed. Examples of radar data corrected using the technique are shown.