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2-1
2. VIDEO SOUNDER OPERATION
2.1 Principle of Operation
The video sounder determines the distance
between its transducer and underwater ob-
jects 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 bot-
tom, part of the sound wave is reflected back
toward the source (transducer). Thus by cal-
culating the time difference between the
transmission of a sound wave and the re-
ception 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 elec-
trical 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 transmis-
sion. Each line represents a snapshot of what
has occurred beneath the boat. A series of
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.
Figure 2-1 Underwater conditions and video sounder display