Onwa KF-667 manual Interpreting the Display, Zero Line, Fish School Echoes, Bottom Echo

3.INTERPRETING THE DISPLAY

3.1Zero 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.

3.2 Fish School Echoes

Fish school echoes will generally be plotted between the zero line and the bottom. Usually the fish school/fish echo is weaker than the bottom echo because its reflection property is much smaller compared to the bottom. The size of the fish school can be ascertained from the density of the display.

Zero line

Shift

Size of fish school

3.3 Bottom Echo

Echoes from the bottom are normally the strongest and are displayed in reddish-brown color (in default color arrangement) but the color 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 color 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 in water depth

Second bottom echo

Rock base

Mud and sand

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