7
pixelization. This bottom depiction is
useful in locating structure, by comparing
relative density as well as depth.
The transmitted sonar signal travels down-
ward, and is reflected back toward the
surface by the bottom or other objects for
display on-screen. The signal does not stop
there - it is reflected downward again by the
surface of the water, and a weak “second
return” is usually visible if the depth range is
sufficient to see it. A second return is shown
in the figure below. Some users use this
second return as an indicator when setting
the sensitivity bias.
If a target is detected between the surface
and the bottom, it is displayed as a fish
symbol. Depending on the strength of the
signal reflected from the object, one of
three different size symbols is used. These
reflected signals are “normalized” for depth,
so that a small fish does not appear to be a
large fish if it is close to the boat.
Since some species of fish tend to be better
reflectors of sonar than others, the strength
of return is not always an accurate indicator of
fish size, however, typically the larger the
fish, the larger the signal return.
USING THE 100ID SERIES
WHAT YOU SEE ON-SCREEN
Soft Mud
Rocky Bottom
Second Return
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