Sea Return; Storm And Rain Squall Returns; Blind Sectors Or Shadow Effect - Simrad CX34 Manual

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3.1.6 Sea return

Not all radar echoes are produced by hard navigation items such
as boats, buoys and land. Some radar echoes may be received from
irregularities on the surface of the water, particularly at close range by
breaking wavecrests, particularly in windy weather and in heavy seas.
These echoes appear on the radar screen on the 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, but the
worst direction is where the wind is blowing towards the ship. The
radar has a sea clutter control, which can be used to minimize the
effects of sea clutter pickup on the screen.

3.1.7 Storm and rain squall returns

The radar can also see echoes from rain or snow. Echoes from 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 rain squalls are not desired, the Rain clutter control can
be adjusted to minimize the effect on the radar screen.

3.1.8 Blind sectors or shadow effect

Funnels, masts or derricks, (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 inten-
sity, 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
CX34/44/54 Operator manual
Chapter 3-5