Furuno GP-7000F Operator's Manual page 115

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.
Bottom echoes
Bottom echoes are normally strongest and displayed in reddish brown or red, but col-
ors and width will vary with bottom material, depth, sea condition, installation, frequen-
cy, pulselength and sensitivity.
Color difference
in sea depth
Second bottom
echo
Bottom material and bottom profile
Bottom profile
A hard and rough bottom appears with a longer tail because it reflects more of the ul-
trasonic 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 ap-
pears 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, overlap-
ping to present a 3D effect.
Slope
Flat bottom
Zero line
Range shifted
Zero line
Rugged bottom
Bottom
with many
undulations
Bottom profile
10. VIDEO SOUNDER OPERATION
10-25