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[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 6.4 and Figure 6.5 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 μs) 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.
Figure 6.4 Decreased target detection distance by S band radar due to precipitation
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Detection distance while it is raining (NM)
Precipitation of 16 mm/hr Pulse width 0.05 μs
Precipitation of 4 mm/hr Pulse width 0.05 μs
Precipitation of 16 mm/hr Pulse width 0.8 μs
Precipitation of 4 mm/hr Pulse width 0.8 μs
Detection distance while it is not raining (NM)
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