Chapter 8: Using the Radar (Digital) 189
echoes are displayed beyond the range of the true target echo, but on the same
bearing.
Blind sectors
Obstructions such as funnels and masts near the radar antenna can obstruct the
radar beam and cause radar shadows or ‘blind sectors’.
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.
D1642-3
True echo
Multiple echoes
D3968-4
81244_4.book Page 189 Thursday, January 31, 2008 1:53 PM
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