Understanding Sonar - Garmin GPSMAP 376C Owner's Manual

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ETTING UP AND SING ONAR

Understanding Sonar

The transducer mounted on your vessel transmits sound waves
toward the bottom of the water in a cone-shaped pattern. When
a transmitted sound wave strikes an underwater object—such as
the bottom, a structure, or a fish—sound is reflected back to the
transducer. The transducer collects the reflected sound waves and
sends the data to the GSD 20 Sounder Module and then to the
GPSMAP 376C to be processed and displayed. The underwater data
is shown on the Sonar display in the order that it is returned; first
returned is the first on the display.
Sonar Page
Generally speaking, if the only thing between the transducer and
the bottom is water, the first strong return comes from the bottom
directly below the transducer and sets the bottom level. Weaker
secondary returns provide the detailed data. Stronger returns display
in darker colors, with red being the strongest return.
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NDERSTANDING ONAR
Understanding the Sonar Display
One of the first things to understand about sonar is that the
transducer sends a beam down to the bottom of the water, much like
the beam of a flashlight. The beam starts small near your vessel and
expands as it gets to the bottom. See
more detailed information.
The Sonar Page does not display a three-dimensional representation
of the underwater environment; the display is in two-dimensions,
much like if you took a picture of an aquarium. Only the depth of
the item in the water appears. The Sonar display does not show you
where an item is located horizontally in the water, as shown in the
drawings below. The fish is not directly above the tree in reality, but
it might look like it is on the Sonar Page.
1'
10'
Tree
20'
Aerial View of the Water
"Transducer Coverage" for
Fish
Tree
Sonar Display
GPSMAP 376C Owner's Manual