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6. INTERPRETING THE DISPLAY
6-3
6.3 Sea Surface Reflections
To reduce sea surface reflections, set the tilt angle to 5° or more so that the upper
edge of the sonar beam does not hit sea surface, or adjust the TVG functions. When
the sonar is used with a narrow tilt angle, the sea surface reflections cover a large area
(up to 300 m to 400 m) as illustrated below.
Sea surface reflections
6.4 Wake
A wake produced by own ship or another ship can be a strong reflecting object when
the sonar is used with a narrow tilt angle. As the wake appears on the screen as a thick
continuous line, it can be easily distinguished from a fish school. On the other hand,
the wake contains a lot of air bubbles which attenuate ultrasonic energy, making it of-
ten difficult to sound beyond the wake.
Wake
Sea surface
Sea surface
Tilt: 0°
Tilt: 5-6°
Tilt angle
indication
Sea surface
reflections
Other
ship
Own
ship
Own ship’s
screw noise
Wake produced
by other ship
Own ship’s
screw noise
Own ship’s wake
(produced when
own ship turns)