Raymarine E120W, Reference Manual

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144 E-Series Networked Display Reference Manual
Multiple echoes
Multiple echoes are not very common but can occur if there is a large target with a
wide vertical surface at a comparatively short range. The transmitted signal will be
reflected back and forth between the target and your own ship, resulting in multiple
echoes, 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 may 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, for wider obstructions there may be a total loss of signal in
the shadow area. There may 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 scales, and the echoes are not repetitive or
consistent in position. With high winds and extreme conditions, echoes from sea
clutter may cause dense background clutter in the shape of an almost solid disc.
D1642-3
True echo
Multiple echoes
D3968-4