A method to estimate subspace via Doppler for ocean clutter suppression in skywave radars

To detect ship targets within short coherent integration time (CIT), the ocean clutter suppressing technique has been used in high frequency (HF) skywave over-the-horizon-radar (OTHR). The clutter cancellation methods in time field are affected by estimate precision of frequency, amplitude and phase. The methods based on subspace are limited by the difficulty in determining the order of clutter subspace, and its performance degrades when the Doppler of target approximates to that of clutter. In this paper, the characteristics of both classes method are considered, and taking advantage of equivalence between clutter eigensubspace and subspace spanned by clutter Doppler frequency vectors, a novel method to estimate subspace via Doppler(ESVID) frequency for ocean clutter suppression in HF skywave radars is proposed, based on which ocean clutter is suppressed without eigen-decomposition. For ESVID method, apriori knowledge about Doppler frequency can be fully used, and only the frequency, without the amplitude and phase, need to be estimated. Finally, tests prove that, when a target appears closely to the clutter in Doppler domain, the ESVID method provides a signal-to-clutter ratio (SCR) improvement of SCR about 10.5dB, 8.5dB and 6.5dB, compared with SVD, CC-FFT and EVD method, respectively.