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6. RADAR
6-19
6.22 How to Interpret the Radar Display
6.22.1 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
ship, bridge, or breakwater. A second, a third or more echoes can be seen on the
screen 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 clutter.
Virtual image
A large target near your ship can show at two positions on the screen. One of the po-
sitions 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 ship. See the figure
shown below for an example of this type of false echo. If your ship gets near a large
metal bridge, for example, a false echo appears on the screen. The echo disappears
after move some distance from the bridge.
Own ship
Target
True
echo
Multiple
echo
Target ship
Your ship
True
echo
False
echo
Mirror image
of target ship
Route for direct reflection
Bridge
Route for
indirect reflection