Matched window processing for mitigating over-the-horizon radar spread Doppler clutter

Ionospheric motion causes spreading of surface clutter in Doppler space which fundamentally limits the detection performance of skywave HF over-the-horizon radars. This paper presents a technique which reduces the effect of so-called “coincident” spread Doppler clutter, i.e. that which results from surface scattering from within the same range resolution cell as the target. The method exploits the spatial correlation of the ionospheric aberration along the geomagnetic field aligned irregularities to obtain a cross-relation between clutter in neighboring range bins. This cross relation is exploited to estimate the Doppler spreading sequence common to neighboring range bins by a technique adapted from blind multichannel system identification. A Chebyshev Doppler window is then designed which is matched to the estimated ionospheric aberration. Simulation and real data results presented here indicate the proposed method provides as much as 10 dB improvement in sidelobe level using a 3 second coherent integration time radar waveform.