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Side scans operate by transmitting a short, high energy, narrow width acoustic wave out each side of the fish.
This high energy acoustic wave hits directly below the fish first (as shown below)
Fish
Acoustic Wave
100 m Range Switch
Target #1
Target #2
10 m
100 m
As the pulse continues to sweep across the bottom, away from the fish, echoes continuously return to the
transducer (see below). The Sonar Processor takes evenly spaced samples of the echo returns (for each side)
which are processed and displayed.
Fish
100 m Range Switch
A look at returning echoes
Returning Echos
Hard Return
Light Return
Acoustic
Hard Return
No Return Echos (Shadow)
Medium Return
Wave
#1
#2
10m
100 m
The larger the amplitude of the return (echo), the greater change of color on the display. The harder the object
(rocks, metal, etc ), the larger the returned echo. The angle of the bottom surface and target angles also impact
the amplitude of the return signal. The left side of target #1 and #2 will produce a larger (harder) return echo than
the top area. When the acoustic wave hits the top of the target, some of the echo is reflected away from the
fish. When the bottom slopes away and down from the fish, only light echo's return from the bottom. When the
bottom slopes upward, medium echo returns are received. If a hard target is positioned on a down or on a up-
sloping bottom, a hard return will result from the target.
If a target is up "off the bottom", as is target #1 and #2, then there will be an area directly behind the target that
will be blocked from the acoustic wave. No echo returns will be received from that area by the fish. When
displaying this area, the display will show a no signal color. This area on the display is called the target's
"shadow".
Each displayed line (one pulse out of the transducer) is 1/2 the screen width wide. The amplitude of the returned
echo samples, during one line, determines the color for each point along the line. When the line is completed
on the display, the display point moves to the next position and the transducer sends out another pulse.
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