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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.
Bottom profile
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 botom 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