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4.3.2 False Image
There is a possibility that non-existing targets may be shown or any existing
targets may not be shown through the image. This image is called ‘virtual image’.
What mainly causes such false image as follows;
1. Shadow
Dipending on the installation position of antenna, the reflection may come back
after colliding against the funnel or mast, which may create ‘shadow’ causing
the virtual image on PPI screen. In this case, the targets that are located at the
shodow direction may not be shown on the screen.
The existence of such a ‘shadow’ can be figured out by checking if there is any
dim image or any unseen part, based on the reflection of sea level.
If the ‘shadow’ occurs, the user needs to memorize the direction in order to
observe the targets with care.
2. Side echo
There may be an image of arc wave line in the same distance from target image
on the screen. This is caused by the side lobe of which beam is radiated from
the antenna.
For this phase, it is easy to make a judgment when targets are fixed.
3. Secondary reflection
Fake images may be displayed as their directions are changed through being
reflected against the funnel or mast, which create shadow.
In this case, the images of targets are located at the mast direction that reflects
the radar wave.
4. Multi-reflection image
Where there are any structures or big-sized vessels that are hidden behind
gigantic vertical line, multiple images by multi-reflection appear.
These images come out at intervals of every lamp line and among the lines, the
closest line to the own ship is the actual image of target.
5. Radar interference
If there is any radars closely located that uses the same frequency, the
interference image by the radar appears on PPI screen. This interference turns
into various spots and appear in forms of many images but as the interference
does not appear in the same place, it can be distinguished from target image.
For the radar interference(‘
’ button), select『ON』in the function to diminish or
get rid of it
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