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Sea Surface Reflections
Wake
As ultrasonic pulses at both edges of the 180˚ sector beam are
always emitted horizontally along the sea surface regardless of
the tilt angle setting, sea surface reflections appear as a thick
line extending across the own ship mark. When the sonar is used
with a narrow tilt angle, the sea surface reflections cover an
extended area as illustrated below.
Figure 9-3 Sea surface reflections
A wake produced by own ship or another ship can be a strong
reflecting object when a narrow tilt angle is used. As the wake
appears as a thick continuous line, it can be easily distinguished
from a fish school. A wake contains many air bubbles which
attenuate ultrasonic energy, making it difficult to sound beyond
the wake.
Figure 9-4 Wake appearance on the display
Sea surface
Reflections
Wake produced
by other ship
Wake produced
by other ship
Wake produced by
own ship when ship is
turned
9-3
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