When Doppler frequency shift is very low for the very slow speed of a ship drawing alongside, it is rather difficult to detect ship's speed with a general CWDopplerRadar.
由于船舶靠岸速度很低，多普勒频移很小，利用一般连续波多普勒雷达检测船舶靠岸速度，困难较大。
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This paper expouds the characteristics of quasi-continuous wave(CW) radar, and compares the pulse Dopplerradar with CW radar and quasi-CW radar.