Space-time adaptive processing for over-the-horizon spread-Doppler clutter mitigation

We address the problem of mitigating spread-Doppler distortion in over-the-horizon (OTH) HF radar returns, caused by motion of electron density irregularities in the ionosphere. For targets with significant radial velocity, discrimination from surface clutter is possible in Doppler space. However, this scheme breaks down in the presence of moving perturbations in the refracting ionosphere, which can cause Doppler spreading of the surface clutter ridge, limiting detection performance, These ionospheric irregularities should be highly correlated in the direction of geomagnetic field lines. We exploit this correlation across range by using neighboring range cells to estimate the spread-Doppler clutter (SDC) in the range cell of interest, and to selectively suppress this clutter, thereby increasing target visibility. For targets directly obscured in Doppler by clutter we enhance target visibility by employing a single additional spatial channel to act as a sidelobe canceler on the main beam