Furuno FSV-84 manual Sea surface reflections

4. SLANT MODE

4.22.3Sea surface reflections

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.

4.22.4Wake

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.

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