Raymarine a65 Operation Instructions Manual page 232

2
1
3
Item Description
1 False echo
2 True echo
3 Passing ship
4 Mast or funnel
5
True echo
6 False echo
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.
Item Description
1 True echo
2 Multiple echoes
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.
Rain or Snow Clutter
The radar can see echoes from rain or snow.
Returns from storm areas and rain squalls consist
of countless small echoes that continuously
change size, intensity and position. These returns
sometimes appear as large hazy areas, depending
232
4
1
on the intensity of the rainfall or snow in the storm
cell. The images in the table below show how the
Rain control can clear up this clutter:
5
Rain
clutter
off
6
D1641-5
Rain
clutter
on
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
2
almost solid disc. Sea clutter can be suppressed
using the sea clutter settings. The images in the
table below show how the sea clutter settings can
clear up some of this clutter:
D1642-4
Sea
clutter
off
Sea
clutter in
auto
LightHouse MFD operation instructions