Understanding The Sonar Display - Garmin GPSMAP 3006C, 3010C Owner's Manual

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.
The Sonar Page does not show a 3-D representation of the underwater
environment. Instead, 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 shown.
The strongest sonar returns appear on your screen as the most intense solid
color (depending on your selected color scheme; red is the default). The weakest
returns appear as the less intense, less solid colors (blue is the default).
The bottom is always the strongest signal, and therefore the most intense color.
The bottom is the continuous, intensely-colored line running across the bottom of
the screen. The GPSMAP 3006C/3010C uses the latest technology in interpreting
bottom signals; it can see through fish, structures, and thermoclines (shown in the
weakest colors). However, large schools of fish or dense structures close to the
bottom can affect water depth return readings.
NOtE: If the GPSMAP 3006C/3010C is unable to track the bottom for any
reason, the digits in the depth window flash on and off to alert you that the unit
is not tracking the bottom.
At the top of the screen, you might see a grouping of intense colors. This area is
surface clutter, which can be caused by waves or any other sonar interference at
the surface of the water. Too much surface clutter can obscure your view of fish.
You can turn down the Gain setting to reduce this surface clutter.
GPSMAP 3006C/3010C Owner's Manual
Between the bottom and the surface clutter, the fish appear as arches. Actual
fish returns might not always appear as perfect arches, due to the speed, fish
orientation, or other conditions. You can turn on the Fish Symbols setting if you
want to see on-screen fish in a fish shape.
Fish Symbols Turned On
The strength of the sonar return can also help you interpret the hardness of the
bottom (the thicker the bottom line, the harder the bottom).
Hard Structure
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Soft Structure