Furuno FR-8122 EU - Manual (Page 71)

2. RADAR OBSERVATION
2-4
2.2.3 Virtual image
A relatively large target close to your ship may be represented 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.
Virtual image
2.2.4 Shadow sector
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 may be produced.
Within this sector targets can not be detected.
Shadow sectors
True
echo
False
echo
Own ship
Target ship
Mirror image
of target ship
Radar
antenna
Radar
mast
Shadow sector