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True
echo
Indirect
echo
Heading
line
True
echo
Indirect
echo
Heading
line
Antenna
Direct
path
Obstruction
(mast, funnel.
etc.)
Indirect
path
Target
Indirect
echo
Bridge
Direct
path
Target
Indirect
path
Own
ship
Figure 4-3 Indirect echoes
4.4 Blind and Shadow Sectors
Funnels, stacks, masts, or derricks in the path
of antenna may reduce the intensity of the ra-
dar beam. If the angle subtended at the antenna
is more than a few degrees a blind sector may
be produced. Within the blind sector small tar-
gets at close range may not be detected while
larger targets at much greater ranges may be
detected. See Figure 4-4.
Vessel taller
than wharf
Wharf
Wharf
Blind sector
(no echo)
Mast, etc. in
path of radar
beam
Size of blind sector
depends on target
size and range.
Figure 4-4 Blind and shadow sectors