How To Understand The Radar Display; False Echoes - Furuno MFD12 Operator's Manual

6.26

How to Understand the Radar Display

6.26.1

False Echoes

Echo signals can appear on the screen at positions where there is no target or disap-
pear where there are targets. You can identify false targets when you understand why
the false echoes appear. A description of false echoes follows.
Multiple echoes
Multiple echoes occur when a transmitted pulse returns from a solid object like a large
vessel, bridge, or breakwater. A second, a third or more echoes can be seen on the
display at two, three or more times the true range of the target as shown below. You
can reduce and sometimes remove these multiple echoes if you decrease the gain, or
correctly adjust the Sea control.
Virtual image
A large target near your vessel can show at two positions on the screen. One of the
positions is the true echo reflected by the target. The other position is a false echo
which is caused by the "mirror effect" of a large object on or near your vessel. See the
figure shown below for an example of this type of false echo. If your vessel gets near
a large metal bridge, for example, a false echo appears on the screen. The echo dis-
appears after move some distance from the bridge.
Target
Own ship
Target ship
Own
ship
Mirror image
of target ship
True
echo
Multiple
echo
True
echo
False
echo
6. Radar
6-25