Furuno 1933, 1943, 1833 manual Interpreting the Sounder Display, Zero line, Bottom echoes

4. VIDEO SOUNDER OPERATION

4.12Interpreting the Sounder Display

4.12.1Zero line

The zero line (sometimes referred to as the transmission line) represents the transducer’s position, and moves off the screen when a deep phased range is used.

Zero line

Shift

Zero line

4.12.2Bottom echo

Echoes from the bottom are normally the strongest and are displayed in the darkest tone, but the tone and width will vary with bottom composition, water depth, frequency, sensitivity, etc.

In a comparatively shallow depth, a high gain setting will cause a second or sometimes a third or a fourth echo to be displayed at the same interval between them below the first echo trace. This is because the echo travels between the bottom and the surface twice or more in shallow depths.

The tone of the bottom echo can be used to help determine the density of the bottom materials (soft or hard). The harder the bottom, the wider the trace. If the gain is set to show only a single bottom echo on mud, a rocky bottom will show a second or third bottom return. The range should be chosen so the first and second bottom echoes are displayed when bottom hardness is being determined.

Intensity difference		Rock base
in water depth		Mud and sand
Second bottom
echo
	Bottom echoes

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