11. Video Sounder Operation; Principle Of Operation - Furuno GP-3500F-D Operator's Manual

11. VIDEO SOUNDER OPERATION

11.1

Principle of Operation

The video sounder determines the distance between its transducer and
underwater objects such as fish, lake bottom or seabed and displays the results
on screen. It does this by utilizing the fact that an ultrasonic wave transmitted
through water travels at a nearly constant speed of 4800 feet (1500 meters) per
second. When a sound wave strikes an underwater object such as fish or sea
bottom, part of the sound wave is reflected back toward the source (transducer).
Thus by calculating the time difference between the transmission of a sound
wave and the reception of the reflected sound wave, the depth to the object can
be determined.
The entire process begins in the display unit. Transmitter power is sent to the
transducer as a short pulse of electrical energy. The electrical signal produced
by the transmitter is converted into an ultrasonic signal by the transducer and
transmitted into the water. Any returning signals from intervening objects (such
as a fish school) are received by the transducer and converted into an electrical
signal. The signals are then amplified in the amplifier section, and finally,
displayed on screen.
The picture displayed is made up of a series of vertical scan lines, one for each
transmission. Each line represents a snapshots are accumulated side by side
across the screen, and the resulting contours of the bottom and fish between the
bottom and surface are displayed.
Note: The procedure in this chapter assume that the echo sounder mode is
active.
Underwater conditions and video sounder display
0
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50
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100
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150
11-1