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The following picture shows the HISTORY screen
with the fish symbols turned off:
Strength of returned echoes
The shading indicates differences in the strength
of the returned echo from the bottom. A black
pattern indicates a strong echo, and light grey
indicates a weak echo. Fish symbols are always
shown in black.
Single fish
Large school
of fish
Small school
of fish
Bottom
Northstar Explorer 443s/443sp Installation and Operation Manual
The strength of the returned echo varies with
several factors, such as:
·
The size of the fish, school of fish or other
object.
·
The depth of the fish or object.
·
The location of the fish or object. The
area covered by the ultrasonic beam is
approximately cone-shaped and echoes are
strongest in the middle.
·
The clarity of water. Particles or air in the water
reduce the strength of the returned echo.
·
The composition or density of the object
or bottom. Mud, weed and sand bottoms
tend to weaken and scatter the sonar signal,
which results in weaker returns. Rock or coral
bottoms concentrate the return signal for
strong returns.
Note: That planing hulls at speed produce air bubbles
and turbulent water that bombard the transducer.
The resulting ultrasonic noise may be picked up by the
transducer and obscure the real echoes.
Large fish
Kelp / weed
Hard bottoms such as
rock or coral show as wide
bands at the bottom of
the screen
Soft bottoms such as
mud, weed and sand
show as narrow bands at
the bottom of the screen
11
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