JRC JMA-9133-SA Instruction Manual page 344

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JMA-9100 Instruction Manual 6.TRUE AND FALSE ECHOES ON DISPLAY
c. 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 6-7.
Radar
scanner
Funnel
d. False Echo by Multiple Reflection
When there is a large structure or ship with a high vertical surface near own ship
as shown in Fig 6-8, multiple refection returns may appear on the radar display.
These echoes appear in the same intervals, of which the nearest echo is the true
echo of the target.
e. Second Time Echoes
The maximum radar detection range depends upon the height of the scanner and
the height of a target as described in the Section 6.1 "RADAR WAVE WITH THE
HORIZON". If a so-called "duct" occurs on the sea surface due to a certain
weather condition, however, the radar beam may propagate to a abnormally long
distance, at which a target may be detected by the radar.
Direct microwave
Secondary reflection
of microwave
Fig 6-7:
False echo by secondary reflection
Fig 6-8: False echo by multiple reflection
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6.4 FALSE ECHOES
HL
False echo from funnel
HL
Actual target