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 CW Doppler Radar.
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。
2
However, short CIT and the resulting low Doppler resolution cannot separate the ship target from the close powerful ocean clutter.
然而短相干积累时间带来的低多普勒分辨率很难从强大的海杂波中区分出舰船。
3
Doppler log is a precise instrument, which is used to measure ship velocity and calculate its voyage on the theory of Doppler Effect of sound wave in water.