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3–1
3. VIDEO SOUNDER OPERATION
3.1 Principle of Operation
The Video Sounder of the GP-1600F determines the distance be-
tween its transducer and underwater objects such as fish, lake bot-
tom or seabed and displays the results on the 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. 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 reflected signals from intervening objects (such as a fish
school) are received by the transducer and converted back into an
electrical signal. It is then amplified in the amplifier section, and
finally, displayed on the screen.
The picture displayed is made up of a series of vertical scan lines,
one for each transmission. Each line represents a "snapshot" of
what has occurred beneath the boat. The series of snapshots are
accumulated side by side across the screen, and the resulting con-
tours of the bottom and fish between the bottom and surface are
displayed.
Figure 3-1 Typical video sounder display