Wavefront adaptive raymode processing for over-the-horizon HF radar clutter mitigation

Detection of surface targets using over-the-horizon radar (OTHR) is extremely challenging due to ionospherically induced Doppler spread clutter. In particular, low Doppler targets are often masked by ground clutter arriving via multipath propagation at different elevation angles, each with a different ionospheric Doppler shift. The wavefront adaptive raymode processing (WARP) approach presented here exploits the azimuthally distributed nature of the clutter return and adaptively estimates the "crinkly" spatial wavefront arriving on each raymode by using its distinct Doppler spectral characteristics. Rather than the plane-wave beamwidth of the array aperture, the raymode resolution of WARP is limited by the wavenumber-extent-spatial-aperture (WESA) product of the clutter return. Thus it is possible to spatially separate clutter raymodes using limited array apertures. Using simulated radar data, WARP is shown to provide a signal-to-clutter-plus-noise ratio (SCNR) improvement of as much as 30 dB over conventional processing for targets buried in Doppler spread clutter.