Chapter 3
TRUE AND FALSE ECHOES ON DISPLAY
3.3
SEA CLUTTER AND RAIN AND SNOW CLUTTER
3-4
3.3 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.
3.3.1 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.
3.3.2 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
3.3.3 COPING WITH SEA CLUTTER AND RAIN AND SNOW
CLUTTER
When the weather is bad and the ocean is rough, reducing the pulse width will reduce the
influence by spurious waves, and also the spurious wave rejection function effectively
works; therefore, the use of short pulse is effective when the weather is bad. By using
image processing functions "3Scan COREL" to "5Scan COREL", it is expected that
spurious waves are further suppressed. Since optimal settings for those items can be
automatically made by using the function mode, it is recommended that STORM or
RAIN be used by selecting the function mode when the weather is bad. For details of the
function mode, see Section "2.14 FUNCTION KEY SETTINGS".
However, these functions may make some targets invisible, particularly targets with
higher speeds.
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