7. FISH FINDER
7-21
7.14 Interpreting the Display
Zero line
The zero line (transmission line) shows the position of the transducer. The line disap-
pears from the screen when the range is shifted.
Bottom echoes
The strongest echoes are from the bottom, and are normally shown in reddish-brown
or red. The colors and the width change with bottom material, depth, sea condition,
installation, frequency, pulse length and sensitivity.
Bottom contour
The tail from a hard bottom is longer than the tail from a soft bottom, because the hard
bottom reflects more of the ultrasonic pulse. An echo from shallow water gives a stron-
ger reflection than the echo received from deep water. A longer bottom tail appears
on slopes, because of the difference in travel time at both edges of the beam angle.
For the rough bottom, echoes are reflected on many different planes, which displays
echoes in many layers, giving a 3D effect.
Second
bottom echo
Difference in sensitivity
Difference in depth
Soft bottom
Hard bottom
Rough bottom
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