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 250DX 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 structure is to operate the 250DX 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 individual dots near the “0” line.
Thermoclines.
Thermoclines are sharp
differences in water temperature.
These are easily identified by the
continuous nature of the return.
Second Returns.
When a sonar signal
is reflected off the bottom back to the
transducer, there is often enough
energy left in the signal to be reflected
off the surface of the water back to the
bottom a second time. Second returns
appear as a slightly weaker bottom
representation exactly twice the depth
of the primary bottom return. The
second return is most likely to occur in
shallow water and in areas of relatively
hard bottom.
Fish ID.
The 250DX uses advanced signal processing to further evaluate any
sonar return between the surface and the bottom. For instance, a small
school of bait fish usually appears as a dense cluster of individual dots. If the
10
USING THE 250DX
WHAT YOU SEE ON SCREEN
Thermocline Second Return
