OTHR Impulsive Interference Suppression in Strong Clutter Background
External interferences can severely degrade the performance of an Over-the-horizon radar (OTHR), so suppression of external interferences in strong clutter environment is the prerequisite for the target detection. The traditional suppression solutions usually began with clutter suppression in either time or frequency domain, followed by the interference detection and suppression. Based on this traditional solution, this paper proposes a method characterized by joint clutter suppression and interference detection: by analyzing eigenvalues in a short-time moving window centered at different time position, clutter is suppressed by discarding the maximum three eigenvalues at every time position and meanwhile detection is achieved by analyzing the remained eigenvalues at different position. Then, restoration is achieved by forward-backward linear prediction using interference-free data surrounding the interference position. In the numeric computation, the eigenvalue decomposition (EVD) is replaced by singular values decomposition (SVD) based on the equivalence of these two processing. Data processing and experimental results show its efficiency of noise floor falling down about 10-20dB.
Ocean clutter suppression for an HF ground wave radar
At HF frequencies, the sea echo or clutter return is quite significant and can mask signals from targets travelling at or near the same Doppler of the resonant (Bragg) ocean waves. This paper presents a systematic method of reducing clutter signals so as to enable detection of targets travelling at speeds near the Bragg Doppler. The algorithm uses a Hankel rank reduction method that assumes that targets and ocean clutter can be modelled as time varying sinusoids. Several examples of clutter suppression are shown from data that was collected at the Cape Race facility. A cooperating vessel was used to show that a clutter supression algorithm may be used to enhance target detection when the target's speed is near the Bragg Doppler frequency.
OTHR impulsive interference detection based on AR model in phase domain
Based on autoregression(AR) model in phase domain, this paper proposes a novel impulsive interference(IMI) detection algorithm for over-the-horizon radar. This is achieved by regarding IMI phase spectrum as complex sinusoid signal and modeling it by AR model. Then we can take the full advantage of the sinusoid signal estimation algorithm. After getting zeros of AR model transfer function, the amount of the contained sinusoid signals and their frequency parameters can be estimated. The angular value of zero is exactly corresponding to IMI position of interest. Details and improvements are also discussed in this paper. This algorithm's operational performance is evaluated using experimental data sets collected from a high frequency surface wave (HFSW) OTHR system, and is proved to be suitable for most types of IMIs.