4. INTERPRETING THE DISPLAY
4-2
4.2 Zero Line
The zero line represents the transducer’s position. It moves off the screen when
a shifted range is used, or is shown at draft depth when ship’s draft is entered.
Zero Line
Range shifted
Zero line
4.3 Bottom Echoes
Bottom echoes are normally strongest and displayed in reddish-brown or red,
but colors and width will vary with bottom material, depth, sea condition,
installation, frequency, pulselength and sensitivity.
A hard and rough bottom appears with a longer tail because it reflects more of
the ultrasonic pulse. Because of their stronger return, shallow echoes appear
wider than deep ones even when all bottom conditions are equal. Also, a longer
bottom tail appears on slopes because of the difference in traveling time at both
edges of the beam angle. In the rugged bottom, echoes are reflected on many
different planes, overlapping to present a 3D effect.
Second bottom
echo
Color difference
Rugged
bottom
Bottom material and bottom profile
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