Relation Between Bottom Echo And Tilt Angle - Furuno FSV-85 MARK-2 Operator's Manual

2.4.3

Relation between bottom echo and tilt angle

The figure below illustrates how two schools of fish "a" and "b" are displayed on the
screen using three different tilt angles.
Case 1: Tilt angle 30° to 40°: This tilt angle will display the entire bottom since it is
captured by the full width of the beam. The school of fish is obscured by the bottom.
Case 2: Tilt angle 10° to 20°: This tilt angle will only display half the bottom since it
is captured by only the lower half of the beam. The school of fish is located above the
bottom.
Case 3: Tilt angle 0° to 5°: This tilt angle may or may not capture the bottom since
the returning bottom echo is weak. The school of fish is located close to the bottom.
Points to consider
• Normally, a vertically distributed school of fish is a better sonar target than the bot-
tom, because it reflects the transmitted pulse back toward the transducer.
• In case 3, both schools of fish "a" and "b" are presented. Generally speaking, how-
ever, midwater schools of fish tend to be larger than schools of fish on the bottom
and they are often displayed near the bottom on the display.
• It is difficult to detect bottom fish when they are not distributed vertically.
Case 1 Case 2
a
a
Case 1
Case 3
b
a
a
Case 2 Case 3
2. HORIZONTAL MODE
a
a
b
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