Reference Manual Part 2

133 Chapter 11: Radar
If the obstruction is relatively narrow, there will be a reduction of the
beam intensity, though not necessarily a complete cut-off. However,
with wider obstructions there can be a total loss of signal in the
shadow area. There might also be multiple echoes which extend
behind the obstruction.
Blind sector effects can normally be minimized by careful selection
of the scanner site prior to installation.
Sea clutter
Radar returns from waves around the vessel can clutter the centre
of the radar picture, making it difficult to detect real targets. Such
‘sea clutter’ usually appears as multiple echoes on the display at
short range, and the echoes are not repetitive or consistent in
position.
In high winds or extreme conditions, sea clutter can produce an
almost solid disc on a radar display.
Rain or snow clutter
Radar detects rain and snow. Returns from storm areas and rain
squalls consist of countless small echoes which continually change
in size, intensity and position.
These returns sometimes appear as large hazy areas, depending
on the intensity of the rainfall or snow in the storm cell.
Mutual radar interference
This can occur when two or more radar-equipped vessels are oper-
ating within range of each other. The interference usually appears
as a spiral of small dots from the display centre, and is most
marked at long ranges.
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