Understanding Sonar; Understanding The Sonar Display - Garmin GPSMAP 296 Pilot'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 a lake, stream, or seabed in a cone-shaped
pattern. When a transmitted sound wave strikes an underwater
object—such as the bottom, a piece of structure, or a fish—sound is
reflected back to the transducer. The transducer collects the reflected
sound waves and sends the data to the GPSMAP 296 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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U S
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. Refer to "Transducer Coverage" for
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 is displayed. 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 may look like they are on the Sonar page.
1'
10'
Tree
20'
Aerial View of the Water
Fish
Tree
Sonar Display
GPSMAP 296 Pilot's Guide