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超视距雷达能够检测很大范围海域内的舰船。但由于电离层的影响迫使多卜勒频移发生变化而玷污了海回波,致使检测性能有时降低。本文中,我们提出了一种消除污染的方法。即在执行经典的快速傅里叶变换(FFT)处理之前,根据海散射谱线的最大熵谱分析修正信号的相位。经相位修正后的信号在质量方面的改善使得谱峰尖锐。本文所介绍的例子中,我们选择的信号包含了安装在船上的应答器的谱线,并用它作为参考线。对于海散射布雷格谱线和应答器谱线来说,谱宽度的减小是很重要的。当布雷格谱线变得尖锐时,舰船的回波就更容易在谱中被检测到。本文提出的消除污染的方法要比简单的用于海情监视的频率漂移的方法包含更多的计算工作量。但从另一方面说,这就可以在相干积累时间内处理多卜勒频移的变化。
OTHR can detect a wide range of ships within the sea. However, due to the influence of the ionosphere, the Doppler shift is forced to pollute the sea echoes and the detection performance sometimes decreases. In this article, we propose a way to eliminate pollution. That is, prior to performing classical Fast Fourier Transform (FFT) processing, the phase of the signal is modified according to the maximum entropy spectral analysis of the sea-scatter line. The quality improvement of the phase-corrected signal makes the peak sharp. In the example presented in this article, the signal we selected contains the spectrum of the transponder installed on board and uses it as a reference line. For the sea-scattered Bragg and transponder lines, the reduction in spectral width is important. As the Bragg spectrum becomes sharp, the ship’s echoes are more easily detected in the spectrum. The method proposed in this paper involves more computational effort than the simple method of frequency drift for sea-state surveillance. On the other hand, however, this makes it possible to handle changes in the Doppler shift within the coherent accumulation time.