Humminbird SINGLEBEAM 405SX Operation Manual page 11

USING THE 405SX
WHAT YOU SEE ON-SCREEN
This range is selected so the bottom representation is typically shown about
down the display.
Bottom. The graphic depiction of the bottom provides the user with an
effective tool for understanding the composition of the bottom. The FSTN type
display uses 4 discrete levels of gray to indicate the intensity of the returned
sonar signal. The 405SX can display even the smallest sonar returns with light
gray pixels. Larger returns are displayed with darker shades of gray. If the
bottom is hard and smooth, the bottom depiction is narrow and dense. If the
bottom is soft mud or sand, the depiction will be thick and less dense. This
indicates that much of the signal is absorbed by the soft bottom. If the bottom
is rocky or rugged in composition, the depiction is of varying density and
textured in appearance.
Wave action also affects the bottom depiction. The information drawn is a
distance measurement, so if the boat is moving up and down over flat bottom,
the bottom depiction often appears in regular variations that match wave
timing.
Structure. Structure is defined as any object physically attached to the bottom.
The sonar configuration of the 405SX is optimized to give the most accurate
depiction of bottom structure possible. Grass, trees, stumps, wrecks or other
debris are accurately displayed, however the depiction of these objects varies
with boat speed and direction. The
best way to learn to interpret
Surface Clutter Rocky Bottom
structure is to operate the 405SX
over a variety of known conditions
and experiment with user functions
to best represent those conditions
on-screen.
Surface Clutter. Surface clutter is
the layer of water near the surface
that is rich in algae and other
growth, and often is aerated by
wind or wave action. This area of
water interferes with sonar
transmission and often appears on-
screen as regular clusters of ind-
Hard Bottom Soft Bottom
ividual dots near the "0" line.
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