Anritsu RA77OUA - False Echoes

3.4 False Echoes
Echoes from targets which do not actually exist in
that direction may appear on the
CRT.
to as " false " or " indirect " echoes. The causes and
phenomena
of such false echoes are listed below.
Virtual
or Ghost Echoes
on the screen as two echoes in two separate
directions. One is a real echo and the other is a
virtual,
or ghost, echo caused by secondary reflection of
emitted pulses by funnels, masts, etc. The former
appears at the correct range and bearing, while the ghost
appears at a range
and-bearilrg-behind- the funnel or the
mast (Fig.
3 - 4).
They are referred
A large target at close range may, at times, appear
Direct Reflection Path
Reflection Path
i
Direction of
Ghost Echo
Heading Marker
CRT screen
Fig. 3 - 4 Virtual or Ghost Echoes
When a target is on the funnel
or mast side, a
series of ghost echoes may appear in the vicinity
of a
real echo.
as mentioned previously. When the intensities
of
reflected waves change, a number of ghosts can be
detected (Fig.
3 - 5). But, they are arranged
asymmetrically with respect to a real echo and vanish
when the ship's heading changes.
The principle of this phenomenon is the same
3 - 4