Sea surface reflections

To reduce sea surface reflections, set the tilt angle to 5° or higher, so the upper edge of the sonar beam does not hit the sea surface, or adjust TVG. When a decreased tilt angle is used, sea surface reflections cover a large area as illustrated below.

Sea surface

Tilt angle

 

 

indication

17˚

 

 

Sea surface

Sea surface

reflections

17˚

 

Figure 2-23 Sea surface reflections

Wake

A wake produced by own ship or another ship can be a strong reflecting object when a decreased tilt angle is used. As the wake appears as a thick continuous line, it can be easily distinguishes from a fish school. A wake contains many air bubbles which attenuate ultrasonic energy, making it difficult to sound beyond the wake.

Other ship

Own ship

Own ship's screw noise

Wake produced

 

by other ship

Own ship's wake

Own ship's

(produced when

screw noise

own ship turned)

Figure 2-24 Wake

2-26

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Image 44
Furuno CH-250 manual Sea surface reflections, Wake