User's Manual

JMA-9100 Instruction Manual > 6.TRUE AND FALSE ECHOES ON DISPLAY > 6.3 SEA CLUTTER AND RAIN AND SNOW

CLUTTER

6－5

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. V: Detection probability of 80 %

V-M

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