Furuno 1823C manual Virtual image, Shadow sectors

2. RADAR OPERATION

Virtual image

A relatively large target close to your ship may show at two positions on the screen. One of them is the true echo directly reflected by the target and the other is a false echo which is caused by the mirror effect of a large object on or close to your ship as shown in the figure below. If your ship comes close to a large metal bridge, for example, such a false echo may temporarily be seen on the screen.

Target ship

Own ship

True echo

Mirror image of target ship

False echo

Virtual image

Shadow sectors

Funnels, stacks, masts, or derricks in the path of the antenna block the radar beam. If the angle subtended at the antenna is more than a few degrees, a non-detecting sector or blind spot may be produced. Within this sector, targets can not be detected.

Radar antenna

Radar mast

Shadow sector

Shadow sectors

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