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Analysis of Sea Clutter Characteristics and Research on Suppression Methods for High Frequency Radar

Author: GaoChao
Tutor: DengWeiBo
School: Harbin Institute of Technology
Course: Information and Communication Engineering
Keywords: characteristics of sea clutter suppression of sea clutter Bragg line bistatic HFGWR
CLC: TN958
Type: Master's thesis
Year: 2011
Downloads: 66
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Abstract


High frequency ground wave radar (HFGWR) which propagate vertically polarized electromagnetic surface can detect targets beyond the horizon. Therefore, HFGWR has been widely used in ocean current mapping and vessel targets detection. Sea clutter which forms the blind zone in Doppler spectrum is the major background and interference for targets detection. The generation of sea clutter can be explained by Bragg scattering resonance. In this paper, we analyze the characteristics of sea clutter and research on the suppression of sea clutter.Firstly,we analyze the frequency and statistical characteristics of sea clutter in monostatic and bistatic HF radar, and scattering characteristics based on scattering cross section model. The first-order scatter from surface waves shows two peaks in the Doppler spectrum, known as first-order Bragg line. The second-order scatter is continuous spectrum and it is about 10 dB lower than the first-order scatter. After orthogonal dual-channel processing, the sea echo shows Rayleigh distribution. The sea clutter will be affected by radar parameters and sea state. As the radar operating frequency or wind speed increase, the amplitude of sea cltter will become larger and then becomes saturated. The wind direction mainly affects the symmetry of sea clutter spectrum.For a bistatic HF radar, we analyze the widening of the first-order Bragg line and the formula of widening value of sea clutter is given. The widening effect of sea clutter will decrease gradually as the range of radar detection increases, so the widening effect can be ignored when radar detect long-range targets. By improving range resolution or angular resolution the widening effect of sea clutter will also decrease.For a bistatic HF radar, the first-order Doppler shift of sea clutter spreads in the bistatic HF radar, so slow speed targets will be easier submerged in sea clutter. In this paper, several of sea clutter suppression methods are presented, and we use actual bistatic radar data to verify these methods. The results have shown that the singular value decomposition (SVD) method and Root clutter cancellation method can suppress the sea clutter and detect targets outside the first-order Bragg line, whereas the targets in the first-order Bragg line are suppressed as well. Since the targets have stronger spatial correlation than sea clutter, we use subspace method to suppress sea clutter and detect targets. This method can detect the targets in and outside the first-order Bragg line.

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