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Chapter 9 TRUE OR FALSE EHOS ON DISPLAY
9.4 FALSE ECHOES
The radar observer may be embarrassed with some echoes that do not exist actually. These false
echoes appear by the following causes that are well known:
9.4.1 SHADOW
When the radar scanner is installed near a funnel or mast, the echo of a target that exists in the
direction of the funnel or mast cannot appear on the radar display because the radar beam is reflected
on the funnel or mast. Whether there are some false echoes due to shadows can be checked
monitoring the sea clutter returns, in which there may be a part of weak or no returns. Such shadows
appear always in the same directions, which the operator should have in mind in radar operation.
9.4.2 SIDE LOBE EFFECT
A broken-line circular arc may appear at the same
range as the main lobe of the radar beam on the radar
display. This type of false echo can easily be
discriminated when a target echo appears isolated.(See
Fig. 9-4-2-1)
HL
Fig. 9-4-2-1
9.4.3 FALSE ECHO BY SECONDARY REFLECTION
When a target exists near own ship, two echoes from the single target may appear on the radar display.
One of those echoes is the direct echo return from the target and the other is the secondary reflection
return from a mast or funnel that stands in the same direction as shown in Fig. 9-4-3-1.
Fig. 9-4-3-1
Direct microwave
Radar
scanner
HL
Secondary reflection
of microwave
Funnel
False echo from funnel
Actual target
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