10. VIDEO SOUNDER OPERATION
10-28
Surface noise
When the sea is rough or the ship passes over a wake, surface noise may appear at
the top of the screen.
Surface noise
Aerated water
When the sea is rough or the ship makes a quick turn, gaps in the bottom echo on the
screen may appear. This is caused by air bubbles which block propagation of the
sound wave. Generally low frequency ultrasonic waves are interrupted more easily
than high ones.
Aerated water
False echo
Every time ultrasonic pulse is transmitted, some radiation escapes on each side of the
beam, called "side lobes." Echoes from side lobes show on the display as false imag-
es as below.
Surface noise
Ultrasonic wave
blocked by
aerated water
False echo
Main
Lobe
Side
Lobe
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