JMA-9172-SA Instruction Manual > 6.TRUE AND FALSE ECHOES ON DISPLAY > 6.3 SEA CLUTTER AND RAIN AND SNOW
CLUTTER
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6.3 SEA CLUTTER AND RAIN AND SNOW
CLUTTER
In addition to the echo required for observing ships and land, radar video image
also includes unnecessary echo, 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 and snow is called "rain and snow clutter," and
those spurious waves must be eliminated by the clutter rejection function.
a. Sea clutter
Sea clutter appears as an image radiating outwardly from the center 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. When waves are large and the sea clutter level is high,
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. Table 6-2 shows the relation between the sea state (SS) showing the size
of waves generated by wind and the radar's detection probability.
Table 6-2： Sea state and probability of target detection
S band radar (probability to detect a target at a distance of 0.4 NM)
RCS
SS1～2 SS2～3 SS3～4 SS4～5
0.1m2 V
i
i. V: Detection probability of 80%
V-M
ii
ii. M: Detection probability of 50%
M-NV
iii
iii. NV: Detection probability of less than 50%
0.5 m2 V V V-M M-NV
1 m2VVVV-M
X band radar (probability to detect a target at a distance of 0.7 NM)
RCS
SS1～2 SS2～3 SS3～4 SS4～5
1m2 V-M M-NV
5 m2 V V-M M-NV
10 m2VVVV-M
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