Chapter 7 Principle of radar system
T
-900 series
7-3
0093142132-00
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False image
The image of a large physical object in a close proximity may appear in two different orientations. One
is a real image and the other is a false image caused by wave reflected on the chimney stack or the
mast, etc.
On the display, one image appears with a right distance and bearing, and another one appears in the
direction of chimney stack, mast, etc. These images may also be generated by being reflected multiple
times from the bridges and quays too.
Passage of direct
reflection
Passage of
secondary
reflection
Mast, etc
Direction of false image
3
1
HU
Real image
False image
Figure 7-5 False image by virtual image
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Duplicate target images
When there is a big reflective surface nearby and perpendicular at a close distance (i.e. when your ship
is passed by a big ship, etc.) radio wave bounces repeatedly between your ship and the other ship.
Therefore, 2 to 4 images may appear at equal range in the direction of this target. The false image
generated by this multi-path reflection is referred as “double targets”. In this case, the closest target is
the real one.
Even if the double targets appear, if the distance and bearing between own ship and the reflective
target changes, the duplicate targets will disappear. Therefore, this false image can be easily
distinguished.
3
1
HU
Double image
Real image
Figure 7-6False image caused by double image
Own ship
Large vessel
