CR40
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/50 MKII Radar operation
Chapter 7
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breaking wavecrests, particularly in windy weather and in heavy seas.
These echoes appear on the radar screen on the very short range scales
as multiple small echoes next to own ship. Under high winds and
extreme conditions the echoes from sea clutter may appear as dense
background of clutter forming the shape of an almost solid disc, as far
as one to three miles in all directions from own ship. The radar has a
control which can be used to minimize the effects of sea clutter pickup
on the screen.
7.1.6 Storm and rain squall returns
The radar can also see echoes from rain or snow. Echoes from storm
areas and rain squalls consist of countless small echoes, continuously
changing in size, intensity, and position. These returns sometimes
appear as large hazy areas on the display depending on the intensity of
the rainfall or snow in the storm cell. The cells usually may be visible
at long distances due to their high altitude above the radar horizon and
are very helpful for observing potential bad weather conditions. If the
returns from storm areas and rain squalls are not desired, the RAIN
clutter control can be adjusted to minimize the effect on the radar
screen.
7.1.7 Blind sectors or shadow effect
Funnels and masts, (when located near the antenna array) may cause
shadows. Shadow areas can be recognized since beyond the obstruction
there will be a reduction of targets and noise intensity, although not
necessarily a complete cutoff seen on the screen. However, if the
shadow angle is more than a few degrees, there will be a blind sector.
In some shadow sectors the beam intensity may not be sufficient to
obtain an echo from a very small object even at close range, despite the
fact that a large vessel can be detected at a much greater range. For this
reason, the angular width and relative bearing of any shadow sector
should be determined at installation. Sometimes shadowing can be seen
on the screen by increasing the radar gain until noise is present. Darker
sectors indicate possible shadowed areas. This information should be
posted near the display unit, and operators must be alert for objects in
these blind sectors.
