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Section 5 Principle
False Echoes
Shadows
Owing to the location of a scanner, surrounding masts and structures may
block the propagation of radar waves in those directions. This can be noticed by
thin or weak shadow sectors in the nearby sea clutter returns. Since these shadows
are fixed due to the physical surroundings on the vessel, it is necessary for the
operator to be aware of them and realize that targets in those sectors may be
weaker or blanked out.
Side lobe
The radar beam has a main beam and weaker side lobes to either side of the
main beam. Because of the side lobers, a series of weaker targets in an arc the
same distance as the real target can show as in the Figure 5-2. This usually occurs
mostly with stronger target returns and it is usually easy to pick out the stronger
echo in the arc as the real target.
False Echo by Secondary Reflection
When an object is in the vicinity of own ship and in some occasion, 2 echoes
appear on he screen that one is true echo and another is a false echo resulted from
secondary reflection of radar beam from ship’s structure such as funnel or mast. In
this case, false echo appears in the direction of funnel or mast from the radar
scanner as Figure 5-3.
DIRECT MICRO WAVE
RADAR SCANNER
SECOND REFELECTION
OF MICRO WAVE
MAST
ACTUAL TARGET
FALSE TARGET
CAUSED BY MAST
Figure 5-2
Figure 5-3
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