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7.3
Sea Clutter and Rain/Snow Clutter
In addition to the echoes required for observing ships and land, radar video images that are displayed
also include undesirable echo images, such as reflection from waves on the sea surface and reflection
from rain and snow. Reflection from the sea surface is called sea clutter and reflection from rain, snow,
and cloud is called rain and snow clutter. Those interfering waves must be eliminated by the clutter
rejection function ([Settings] – [Signal Process] – [Video Noise Rejection]). (Refer to "13.2 Setting
Radar Signal Processing".)
7.3.1
Sea clutter
Sea clutter appears as an image radiating outwardly from the centre of the radar display and changing
depending on the size and the shape of waves. Generally, as waves become larger, image level of the
sea clutter is intensified and the clutter far away is also displayed. In this case, it is difficult to
distinguish sea clutter from a small boat whose reflection intensity is weak. Accordingly, it is necessary
to properly adjust the sea clutter rejection function.
The following tables show the relation between the sea state (SS) showing the size of waves
generated by wind and the radar's detection probability.
Sea State and Probability of Target Detection
RCS
SS1 to 2
0.1 m
2
0.5 m
2
1 m
2
S band radar (probability to detect a target at a range of 0.4 NM)
RCS
SS1 to 2
1m
2
V-M
5 m
V
2
10 m
2
V
X band radar (probability to detect a target at a range of 0.7 NM)
V:
Detection probability of 80 %
M: Detection probability of 50 %
NV: Detection probability of less than 50 %
Section 7 True and False Echoes on Display
SS2 to 3
SS3 to 4
V
V-M
M-NV
V
V
V-M
V
V
V
SS2 to 3
SS3 to 4
M-NV
V-M
M-NV
V
V
SS4 to 5
M-NV
V-M
SS4 to 5
V-M
7-4
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