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3-4
Suppressing Seabed and Sea Surface Reflections in
Shallow Waters
Data setting window: TVG•TX, OUTPUT
In shallow fishing grounds with hard or rocky bottom, seabed
reflections often interfere with wanted fish echoes and they can
not be eliminated sufficiently with the aforementioned TVG and
AGC controls, especially when the TILT is set to a larger angle
in order to track fish schools approaching within 400 m. In such
cases try to reduce the output power by adjusting the OUTPUT
control instead of turning down the gain. The picture becomes
clearer when output power is reduced rather than when the GAIN
is decreased as illustrated below.
TVG and AGC
adjusted with
OUTPUT kept high
OUTPUT decreased
with GAIN kept
constant
WRONG
METHOD
CORRECT
METHOD
Fish echo
Fish echo
Seabed echo
False seabed echo
Surface echo
Figure 3-3 How to suppress seabed and sea surface reflections
in shallow waters
Rejecting Sonar Interference and Noise
While observing the sonar picture, you may encounter occasional
or intermittent noise and interference. These are mostly caused
by on-board electronic equipment, engine or propeller noise, or
electrical noise from other sonars being operated nearby.