y
yy
yyy
6.3 Sea Clutter and Rain and Snow Clutter
As shown in Table 6.3, the number of SS increases as the wind speed becomes high and the waves
become large. Table 6.2 reveals that detection probability decreases from V (80 %) to NV (less than
50 %) as the number of SS increases. Therefore, even if the sea state is calm and a target clearly
appears on the radar display, when the sea state becomes rough, target detection probability decreases
resulting in difficulty of target detection by the radar.
Table 6.3 Relation between Douglas sea state and average wind speed and significant wave
height
Sea state
Average wind speed (kn)
Significant wave height (m)
0 <4
<0.2
1 5-7
0.6
2 7-11
0.9
3 12-16
1.2
4 17-19
2.0
5 20-25
3.0
6 26-33
4.0
6
Significant wave height: an average of top N/3 higher waves when the
number of waves detected within a constant time
duration is N
For example, in the case of a standard marine buoy, RCS of X band radar is 5 m2 as shown in Table 6.1.
When observing such a target in the sea state (SS3) in which significant wave height exceeds 1.2
meters, detection probability is M-NV, as shown in Table 6.2, which indicates 50 % or less.
[II] Rain and snow clutter
Rain and snow clutter is a video image that appears in a location where rain or snow is falling. The
image changes according to the amount of rain (or the amount of snowfall). As precipitation
increases, the image of rain and snow clutter becomes intensified on the radar display, and in the case
of localized heavy rain, an image similar to the image indicating land is displayed in some cases.
Furthermore, because radio waves tend to attenuate due to rain and snow, the ability to detect a target
in the rain and snow clutter or a target beyond the rain and snow clutter may decrease. The amount of
attenuation depends on the transmission frequency, antenna beam width, and the pulse length. Figure
6.3 and Figure 6.4 show examples in which detection distance is reduced due to the influence of
precipitation. Because of this, a target, which clearly appeared up to 10 NM by an X band radar
(pulse width of 0.8
μ
s) when it was not raining, may become dimly visible up to 5 NM when the
amount of rain becomes 4 millimeters per hour. Furthermore, when comparing the X band radar with
the S band radar, target detection distance decreases less when an S band radar is used, which means it
is influenced less by precipitation.
6-6
Summary of Contents for JMA-5912-6
Page 2: ......
Page 17: ...xi NKE 2103 6 Scanner Unit NKE 2254 7 9 Scanner Unit Warning Label Warning Label...
Page 18: ...xii NKE 1130 Scanner Unit NQE 3151A Junction Box Warning Label Warning Label...
Page 19: ...xiii NQE 3141 4A 8A Interswitch Unit NBA 5111 Power Supply Warning Label Warning Label...
Page 20: ...xiv NQE 3167 Power Control Unit Warning Label...
Page 22: ...xvi Scanner Unit Type NKE 2254 9 9 feet NDC 1477 Radar Process Unit Desktop Type...
Page 23: ...xvii NWZ 170 Monitor Unit Desktop Type NCE 5171 Operation Unit Desktop Type...
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Page 48: ...1 7 Fig 1 1 Outside Drawing of NKE 2103 6 SCANNER UNIT...
Page 49: ...1 8 1 4 Exterior Drawings y 1 Fig 1 2 Outside Drawing of NKE 2254 7 SCANNER UNIT...
Page 50: ...1 9 Fig 1 3 Outside Drawing of NKE 2254 9 SCANNER UNIT...
Page 51: ...1 10 1 4 Exterior Drawings y 1 Fig 1 4 Outside Drawing of NKE 1130 SCANNER UNIT...
Page 52: ...1 11 Fig 1 5 Outside Drawing of NWZ 170 MONITOR UNIT Option...
Page 54: ...1 13 Fig 1 7 Outside Drawing of NDC 1477 RADAR PROCESS UNIT...
Page 55: ...1 14 1 4 Exterior Drawings y 1 Fig 1 8 Outside Drawing of NCE 5171 OPERATION UNIT...
Page 56: ...1 15 Fig 1 9 Outside Drawing of NQE 3151A JUNCTION BOX...
Page 57: ...1 16 1 4 Exterior Drawings y 1 Fig 1 10 Outside Drawing of NQE 3141 4A INTERSWITCH UNIT Option...
Page 58: ...1 17 Fig 1 11 Outside Drawing of NQE 3141 8A INTERSWITCH UNIT Option...
Page 60: ...1 19 Fig 1 13 Outside Drawing of NQE 3167 POWER CONTROL UNIT Option...
Page 68: ...2 3 Lower left of the display Upper right of the display...
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Page 421: ...APPENDIX...
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Page 438: ...32bit bus BP BZ VD TI MTR PWRCNT P12V 12V RGB Fig 2 Block Diagram of JMA 5932 12 RADAR...
Page 442: ...Fig 6 Terminal Board Connection Diagram of RADAR and INTERSWITCH Unit Option...
Page 443: ...Fig 7 Power System Diagram of JMA 5912 6 JMA 5922 7 9 RADAR...
Page 445: ...Fig 9 Internal Connection Diagram of NDC 1477 RADAR PROCESS UNIT...
Page 446: ...Fig 10 Internal Connection Diagram of NQA 2123 INTERFACE UNIT...
Page 447: ...Fig 11 Internal Connection Diagram of NCE 5171 OPERATION UNIT...
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